Thomas Horstemeyer Docket No.: 222117-2220 BIS(PHOSPHINO)BORYL SUPPORTED NI COMPLEXES AND METHOD OF USE THEREOF CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to U.S. provisional application entitled “Bis(phosphino)boryl supported NI complexes and method of use thereof” having serial number 63/382,187 filed on November 3, 2022, which is entirely incorporated herein by reference. FEDERAL SPONSORSHIP This invention was made with government support under Grant No. CHE-2102433, awarded by U.S. National Science Foundation. The government has certain rights in the invention. BACKGROUND The development of new catalysts for Ni-catalyzed olefin oligomerization and studies of the reaction mechanisms are of interest in aFDGHPLD^DQG^YDULRXV^LQGXVWULHV^^^/LQHDU^Į- olefins (LAOs) are used in fuel, petro-, and fine chemistry, and studying the conversion of ethylene to higher olefins is of importance as the market for LAOs expands. SUMMARY Embodiments of the present disclosure provide for the catalytic transformation to convert ethylene and/or D-olefins to higher olefins. In an embodiment, the present disclosure provides for a composition comprising: (
RPQP)NiX compounds having the following structure:
, wherein Q is B, Al, Ga, In, or Tl, wherein each R is independently selected from an alkyl or aryl group, where X is a halogen, acetoxy group (OAc), or polyatomic ion (e.g., BF
4-, PF
6-, BAr
4- (Ar = aryl group) etc.).
Thomas Horstemeyer Docket No.: 222117-2220 In an embodiment, the present disclosure provides for a method of making linear alpha olefins (LAO)s and internal olefins, comprising reacting ethylene with the composition described above or compositions described herein. BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present disclosure will be more readily appreciated upon review of the detailed description of its various embodiments, described below, when taken in conjunction with the accompanying drawings. Figure 1 illustrates isomerization of 1-butene. Reaction conditions: (
RPBP)NiBr ^^^^^^^^PRO^^^(W$O&O
2 ^^^^^^^PRO^^^XVLQJ^WROXHQH^DV^WKH^VROYHQW^^^^P/^WRWDO^IRU^HDFK^ UHDFWLRQ^^^^^^SVLJ^^-butene at room temperature for 120 min. Figure 2 illustrates an excerpt of the Gibbs energy profile for the reaction of two equivalents of ethylene and [(
tBuPBP)Ni]
+ (5) to form a product 6 with two ethylene ligands and a dissociated phosphine. Relative Gibbs energies at 298 K and 1 M in kcal mol
í^. Hydrogen atoms on the (
RPBP)Ni moiety have been omitted for clarity. Figure 1 illustrates frontier molecular orbitals involved in TS1, which provides C–C formation between two equivalents of ethylene. Figure 2 illustrates an excerpt of the Gibbs energy profile for Ni-mediated C–C coupling of two ethylene ligands (TS2) to ultimately form complex 8, which possesses a Ni/CH
2 agnostic interaction. Relative Gibbs energies at 298 K and 1 M in kcal mol
í^. Hydrogen atoms on the (
RPBP)Ni system have been omitted for clarity. Figure 3 illustrates an excerpt of the Gibbs energy profile for the reaction of ethylene DQG^^^^ȕ-hydride eliminations and hydride transfer). Relative Gibbs energies at 298 K and 1 M in kcal mol
í^. Hydrogen atoms on the (
RPBP)Ni system have been omitted for clarity. Figure 4 illustrates an excerpt of the Gibbs energy profile for the reaction of ethylene and 5 (hydride orbiting and formation of 1-butene). Relative Gibbs energies at 298 K and 1 M in kcal mol
í^. Hydrogen atoms on the (
RPBP)Ni system have been omitted for clarity. Figure 7, Scheme 1 illustrates previously proposed mechanisms for Ni-mediated ethylene oligomerization. Figure 8, Scheme 2 illustrates examples of previously reported reactions of olefins with PBP-Ni and related PB-Ni complexes and this work.
Thomas Horstemeyer Docket No.: 222117-2220 Figure 9(A) illustrates control experiments using other Ni pre-catalysts without the
RPBP ligand, which establishes the importance of the
RPBP ligand to successful catalysis. Figure 9(B) illustrates attempts for propylene dimerization using (
RPBP)Ni complexes 1–3. Figure 10 illustrates selectivity of ethylene oligomerization using (
tBuPBP)NiBr (2), (
PhPBP)NiBr (3) and (
CyPBP)NiBr (4). Figure 11 illustrates halide abstraction from complex 2 to give cationic complex 5. Figure 12 illustrates observed products using (
tBuPBP)NiBr with MAO under ethylene, propylene, or a mixture of propylene with ethylene. DETAILED DESCRIPTION In general, the present disclosure provides for catalytic precursors, methods of making catalytic precursors, and method of catalytic alkene oligomerization reactions. Additional details are provided below, in Example 1 and in the claims. Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims. Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit (unless the context clearly dictates otherwise), between the upper and lower limit of that range, and any other stated or intervening value in that stated range, is encompassed within the disclosure. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described. As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other
Thomas Horstemeyer Docket No.: 222117-2220 several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible. Embodiments of the present disclosure will employ, unless otherwise indicated, techniques of chemistry, inorganic chemistry, synthetic chemistry, and the like, which are within the skill of the art. Such techniques are explained fully in the literature. The following description and examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to perform the methods and use the compositions and compounds disclosed and claimed herein. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C, and pressure is in bar or psig. Standard temperature and pressure are defined as 25 °C and 1 bar. Before the embodiments of the present disclosure are described in detail, it is to be understood that, unless otherwise indicated, the present disclosure is not limited to particular materials, reagents, reaction materials, manufacturing processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It is also possible in the present disclosure that steps can be executed in different sequence where this is logically possible. Different stereochemistry is also possible, such as products of cis or trans orientation around a carbon–carbon double bond or syn or anti addition could be both possible even if only one is drawn in an embodiment. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a support” includes a plurality of supports. In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings unless a contrary intention is apparent. Definitions: By “chemically feasible” is meant a bonding arrangement or a compound where the generally understood rules of organic structure are not violated. The structures disclosed herein, in all of their embodiments are intended to include only “chemically feasible” structures, and any recited structures that are not chemically feasible, for example in a
Thomas Horstemeyer Docket No.: 222117-2220 structure shown with variable atoms or groups, are not intended to be disclosed or claimed herein. However, if a bond appears to be intended and needs the removal of a group such as a hydrogen from a carbon, the one of skill would understand that a hydrogen could be removed to form the desired bond. The term "substituted” refers to any one or more hydrogen atoms on the designated atom (e.g., a carbon atom) that can be replaced with a selection from the indicated group (e.g., halide, hydroxyl, alkyl, and the like), provided that the designated atom’s normal valence is not exceeded. As used herein, the term “optionally substituted” typically refers to from zero to four substituents, wherein the substituents are each independently selected. Each of the independently selected substituents may be the same or different than other substituents. For example, the substituents (e.g., an R type group) of a formula may be optionally substituted (e.g., from 1 to 4 times) with independently selected H, halogen, hydroxy, acyl, alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclo, aryl, heteroaryl, alkoxy, amino, amide, thiol, sulfone, sulfoxide, oxo, oxy, nitro, carbonyl, carboxy, amino acid sidechain, amino acid, etc. In an embodiment, substituted includes substitution with a halogen. As used herein, a “derivative” of a compound refers to a chemical compound that may be produced from another compound of similar structure in one or more steps, as in replacement of H by an alkyl, acyl, amino group, etc. As used herein, “aliphatic” or “aliphatic group” refers to a saturated or unsaturated, linear or branched, cyclic (non-aromatic) or heterocyclic (non-aromatic), hydrocarbon or hydrocarbon group, where each can be substituted or unsubstituted, and encompasses alkyl, alkenyl, and alkynyl groups, and alkanes, alkene, and alkynes, for example, substituted or unsubstituted. As used herein, “alkane” refers to a saturated aliphatic hydrocarbon which can be straight or branched, having 1 to 40, 1 to 20, 1 to 10, or 1 to 5 carbon atoms, where the stated range of carbon atoms includes each intervening integer individually, as well as sub-ranges. Examples of alkane include, but are not limited to methane, ethane, propane, butane, pentane, and the like. Reference to “alkane” includes unsubstituted and substituted forms of the hydrocarbon moiety. As used herein, “alkyl” or “alkyl group” refers to a saturated aliphatic hydrocarbon, which can be straight or branched, having 1 to 40, 1 to 20, 1 to 10, or 1 to 5 carbon atoms, where the stated range of carbon atoms includes each intervening integer individually, as well
Thomas Horstemeyer Docket No.: 222117-2220 as sub-ranges. Examples of alkyl groups include, but are not limited to methyl, ethyl, n- propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, and s-pentyl. Reference to “alkyl” or “alkyl group” includes unsubstituted and substituted forms of the hydrocarbon moiety. As used herein, “alkene” (also referred to as an “olefin”) refers to an aliphatic hydrocarbon which can be straight or branched, containing at least one carbon-carbon double bond, having 2 to 40, 2 to 20, 2 to 10, or 2 to 5 carbon atoms and can also be have 4 to 30 carbons, 4 to 21 carbons, or 6 to 20 carbons, where the stated range of carbon atoms includes each intervening integer individually, as well as sub-ranges. Examples of alkene groups include, but are not limited to, ethylene, propylene, butene, 1-pentene, 1-hexene, isobutene and the like. Reference to “alkene” includes unsubstituted and substituted forms of the hydrocarbon moiety. As used herein, “alkyl” or “alkyl group” refers to a saturated aliphatic hydrocarbon, which can be straight or branched, having 1 to 40, 1 to 20, 1 to 10, or 1 to 5 carbon atoms, where the stated range of carbon atoms includes each intervening integer individually, as well as sub-ranges. Examples of alkyl groups include, but are not limited to methyl, ethyl, n- propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, and s-pentyl. Reference to “alkyl” or “alkyl group” includes unsubstituted and substituted forms of the hydrocarbon moiety. “Aryl”, as used herein, refers to C
5-C
20-membered aromatic, heterocyclic, fused aromatic, fused heterocyclic, biaromatic, or bihetereocyclic ring systems. In an aspect, “aryl”, can include 5-, 6-, 7-, 8-, 9-, and 10-membered single-ring aromatic groups that may include from zero to four heteroatoms, for example, functional groups that correspond to benzene, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine and pyrimidine, and the like. Those aryl groups having heteroatoms in the ring structure may also be referred to as “aryl heterocycles” or “heteroaromatics”. The aromatic ring can be substituted at one or more ring positions with one or more substituents including, but not limited to, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino (or quaternized amino), nitro, sulfhydryl, imino, amido, phosphonate, phosphinate, carbonyl, carboxyl, silyl, ether, alkylthio, sulfonyl, sulfonamido, ketone, aldehyde, ester, heterocyclyl, aromatic or heteroaromatic moieties, -CF
3, -&1^^DQG^ combinations thereof. The term “aryl” also includes polycyclic ring systems (C
5-C
30) having two or more cyclic rings in which two or more carbons are common to two adjoining rings (i.e., “fused rings”) wherein at least one of the rings is aromatic, e.g., the other cyclic ring or rings can be
Thomas Horstemeyer Docket No.: 222117-2220 cycloalkyls, cycloalkenyls, cycloalkynyls, aryls and/or heterocycles. Examples of heterocyclic rings include, but are not limited to, benzimidazolyl, benzofuranyl, benzothiofuranyl, benzothiophenyl, benzoxazolyl, benzoxazolinyl, benzthiazolyl, benztriazolyl, benztetrazolyl, benzisoxazolyl, benzisothiazolyl, benzimidazolinyl, carbazolyl, 4aH carbazolyl, carbolinyl, chromanyl, chromenyl, cinnolinyl, decahydroquinolinyl, 2H,6H- 1,5,2-dithiazinyl, dihydrofuro[2,3 b]tetrahydrofuran, furanyl, furazanyl, imidazolidinyl, imidazolinyl, imidazolyl, 1H-indazolyl, indolenyl, indolinyl, indolizinyl, indolyl, 3H-indolyl, isatinoyl, isobenzofuranyl, isochromanyl, isoindazolyl, isoindolinyl, isoindolyl, isoquinolinyl, isothiazolyl, isoxazolyl, methylenedioxyphenyl, morpholinyl, naphthyridinyl, octahydroisoquinolinyl, oxadiazolyl, 1,2,3-oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, oxazolidinyl, oxazolyl, oxindolyl, pyrimidinyl, phenanthridinyl, phenanthrolinyl, phenazinyl, phenothiazinyl, phenoxathinyl, phenoxazinyl, phthalazinyl, piperazinyl, piperidinyl, piperidonyl, 4-piperidonyl, piperonyl, pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolidinyl, pyrazolinyl, pyrazolyl, pyridazinyl, pyridooxazole, pyridoimidazole, pyridothiazole, pyridinyl, pyridyl, pyrimidinyl, pyrrolidinyl, pyrrolinyl, 2H-pyrrolyl, pyrrolyl, quinazolinyl, quinolinyl, 4H-quinolizinyl, quinoxalinyl, quinuclidinyl, tetrahydrofuranyl, tetrahydroisoquinolinyl, tetrahydroquinolinyl, tetrazolyl, 6H-1,2,5-thiadiazinyl, 1,2,3- thiadiazolyl, 1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl, 1,3,4-thiadiazolyl, thianthrenyl, thiazolyl, thienyl, thienothiazolyl, thienooxazolyl, thienoimidazolyl, thiophenyl and xanthenyl. One or more of the rings can be substituted as defined above for “aryl”. As used herein, “halo”, “halogen”, “halide”, or “halogen radical” refers to a fluorine, chlorine, bromine, iodine, and astatine, and radicals thereof. Further, when used in compound words, such as “haloalkyl” or “haloalkenyl”, “halo” refers to an alkyl or alkenyl radical in which one or more hydrogens are substituted by halogen radicals. Examples of haloalkyl include, but are not limited to, trifluoromethyl, trichloromethyl, pentafluoroethyl, and pentachloroethyl. As used herein, “cyclic” hydrocarbon refers to any stable 4, 5, 6, 7, 8, 9, 10, 11, or 12 membered, (unless the number of members is otherwise recited), monocyclic, bicyclic, or tricyclic cyclic ring. As used herein, “olefin” is a hydrocarbon that includes at least one double bond. An alpha olefin ^Į-olefin) has a double bond at the alpha or primary position, whereas an internal olefin includes a double bond within the hydrocarbon chain that is not in the alpha position.
Thomas Horstemeyer Docket No.: 222117-2220 As used herein, the term “purified” and like terms relate to an enrichment of a molecule or compound relative to other components normally associated with the molecule or compound in a native environment. The term “purified” does not necessarily indicate that complete purity of the particular molecule has been achieved during the process. A “highly purified” compound as used herein refers to a compound that is greater than 90% pure. General Discussion The present disclosure provides for catalytic precursors, methods of making catalytic precursors, method of catalytic alkene oligomerization reactions, methods of converting ethylene to linear alpha olefins or internal olefins. In some aspects the present disclosure provides for (
RPQP)NiBr (Q = B, Al, Ga, In, or Tl, R = an alkyl or aryl group, for example t%X^^3K^^RU^&\^^;^ ^KDORJHQ^^H^g., Br), OAc, or polyatomic ion) catalyst precursors and catalytic ethylene oligomerization reaction methods. Example 1 provides illustrations of the versatility of the present disclosure. In one aspect, the present disclosure provides for methods that illustrate ethylene dimerization is generally selective for the formation of terminal 1-butene, and that the features of catalysis are dependent on ligand identity. The reactions proceed by using (
tBuPBP)NiOAc (1) without co-catalyst, as well as mixing (
RPBP)NiBr with Ag
+ or Na
+ salts, alkylaluminum, or other Lewis acids (e.g., BF
3, BBr
3, and AlCl
3). The (
PhPBP)Ni complex shows significant activity for the production of butenes with a TOF up to 274(34) mol
butenes·mol
Ni í^·s
í^ (41(1)% selective for 1-butene), while the (
tBuPBP)Ni complex shows good selectivity for 1-butene with a TOF up to 33(2) mol
butenes·mol
Ni í^·s
í^ (87(0)% selective for 1-butene). The PBP-Ni activation of ethylene and proposed mechanism is unique for the conversion of ethylene to higher olefins. Additional details are provided in Example 1. In an aspect, the present disclosure provides for Ni catalysts that convert ethylene to linear alpha olefins with high reaction rates and selectivity. A characteristic of these catalysts is the presence of a Lewis acidic moiety bonded to the Ni center. In an aspect, the present disclosure provides for (
RPQP)NiX, where Q is B, Al, Ga, In, or Tl, where each R can be independently selected from an alkyl or aryl group such as a t- butyl group (tBu), phenyl group (Ph), or a cyclohexyl group (Cy), where X is a halogen like Br or X is acetoxy group (OAc) or a polyatomic ion such as BF
4-, PF
6-, BAr
4- (Ar = aryl
Thomas Horstemeyer Docket No.: 222117-2220 group), etc. The (
RPQP)NiX compound can have the following structure:
. In a particular aspect, the present disclosure provides for (
RPBP)NiX, where each R can be independently selected from an alkyl or aryl group such as a t-butyl group (tBu), phenyl group (Ph), or a cyclohexyl group (Cy), where X is a halogen like Br or X is acetoxy group (OAc) or a polyatomic ion such as BF
4- or PF
6-. In an aspect, each R can be the same. The (
RPBP)NiX compound can have the following structure:
, where X is a halogen like Br or X is acetoxy group (OAc) or a polyatomic ion such as BF
4- or PF
6-. The present disclosure provides for the catalytic transformation to convert ethylene and/or D-olefins (e.g., C3 to C20), to higher olefins (C5 to C21 or C6 to C20 oligomers). For example, Figure 12 illustrates the observed products using (
tBuPBP)NiBr with MAO under ethylene, propylene, or a mixture of propylene with ethylene. In particular, the present disclosure provides for selective coupling of ethylene and 1-hexene to give 1-octene. Each of the reactions can optionally be conducted in a single container (e.g., “one pot synthesis”). In an embodiment, each of the reactions can be conducted at about room temperature. The reaction time for each can be about 5 mins to 5 days, about 12 to 36 hours, or about 24 hours. In an embodiment the amount of (
RPQP)NiX can be about 0.1 to 10 μmol. In an embodiment, the amounts of other components such as Ag
+ or Na
+ salts, alkylaluminum, or other Lewis acids (e.g., BF
3, BBr
3, and AlCl
3) can each independently be about 1 to 1000 equivalents, about 2 to 20 equivalents, or about 2 to 15 equivalents relative to catalyst. Additional details are provided in Example 1. Ethylene (and/or the D-olefin) pressure can vary from ambient (e.g., about 15 psi) up to high pressures (e.g., up to 2000 psi or greater). In an embodiment, the products (e.g., butenes (e.g., 1-butene)) can be produced with about 50, 60, 70, 80, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99, each up to 100% selectivity (e.g., about 50 to 100%). In one aspect the yield is about 50, 60, 70, 80, or 90, each up to 100% (e.g., about 50 to 100%, about 70 to 100%, or about 80 to 100%). In an embodiment,
Thomas Horstemeyer Docket No.: 222117-2220 the product can be produced with high selectivity (e.g., about 70% to 100%), for example for 1-butene. In addition to the (
RPQP)NiX, the following materials can be included in the reaction: solvent (e.g., toluene, etc.), air (e.g., at ambient to 5000 psi), and N
2 (e.g., at ambient to 5000 psi). In regard to each of the reactions described herein, each can optionally be conducted in a single container and at about room temperature. The reaction time for each can be about 5 mins to 5 days, about 12 to 36 hours, or about 24 hours. In an embodiment the amount of compound used (e.g., (
RPQP)NiX) can be about 0.1 to 10 μmol. In an embodiment, the amounts of other components such as Ag
+ or Na
+ salts, alkylaluminum, or other Lewis acids (e.g., BF
3, BBr
3, and AlCl
3) can each independently be about 1 to 1000 equivalents, about 2 to 20 equivalents, or about 2 to 15 equivalents relative to catalyst. Ethylene (and/or the D- olefin) pressure can vary from ambient up to high pressures. EXAMPLES Now having described the embodiments of the disclosure, in general, the examples describe some additional embodiments. While embodiments of the present disclosure are described in connection with the example and the corresponding text and figures, there is no intent to limit embodiments of the disclosure to these descriptions. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of embodiments of the present disclosure. Example 1: Introduction Catalytic oligomerization of ethylene is an important commercial method for the proGXFWLRQ^RI^OLQHDU^Į-olefins (LAOs), which have extensive uses in fuel, petro-, and fine chemistry.
1-4 Each year, > 3.5 million tons of LAOs are produced globally, and the annual growth rate of world consumption of LAOs forecasted to be approximately 4% during the 2019–2024 period.
5,6 Since the first discovery of the "nickel effect" by Ziegler and Holzkamp in the 1950s,
7 the field of nickel catalyzed olefin oligomerization has become one of intense study. Thus, the development of new catalysts for Ni-catalyzed olefin oligomerization and studies of the reaction mechanisms continue to be of interest to academia and industry.
8-10 Another important milestone in this field was the development of the bidentate P–O ligated
Thomas Horstemeyer Docket No.: 222117-2220 Ni complex by Keim and coworkers,
11 which ultimately led to the commercialization of the Shell higher olefin process (SHOP) that is used for the production of over one million tons of Į-olefins every year.
2,12-13 This success has encouraged recent studies with the goal of pursuing novel ligand structures to develop new fundamental understanding of how ligand/catalyst structure can impart new types of reactivity.
12 The generally accepted mechanism for Ni-mediated ethylene oligomerization (e.g., the SHOP process) is the Cossee-Arlman mechanism (Figure 7, left)
5,9,14-15 in which the reaction is initiated from a Ni–H/alkyl intermediate followed by ethylene insertion steps ^FKDLQ^JURZWK^^^7KH^IRUPDWLRQ^RI^ROHILQ^SURGXFWV^LV^JHQHUDOO\^SURSRVHG^WR^RFFXU^YLD^ȕ-H elimination from a Ni-alkyl intermediate followed by net olefin dissociation. Chain propagaWLRQ^LV^QRUPDOO\^FRQWUROOHG^E\^WKH^UDWLR^RI^HWK\OHQH^LQVHUWLRQ^DQG^ȕ-H elimination rates,
10 DQG^IUHTXHQWO\^6FKXO]í)ORU\^GLVWULEXWLRQV^RI^HWK\OHQH^ROLJRPHUV^DUH^REWDLQHG^
16-18 Another possible mechanism for Ni-catalyzed ethylene oligomerization involves the formation of a metallacycle similar to the reactions using Cr catalysts,
9,19 which is normally proposed in the reaction of a Ni pre-catalyst with a Lewis acid activator (e.g., BF
3).
20 This type of mechanism has been suggested to be energetically viable based on DFT modeling of phosphine ligated Ni(0) catalyzed ethylene dimerization processes (Figure 7, right).
2,21 Experimental evidence for a Ni metallacycle mechanism (Figure 7, right) was reported by Grubbs and coworkers using a nickel-based metallacyclopentene complex in the 1970s.
22-26 Pincer ligands have been widely used in transition-metal-mediated catalysis due, in part, to their tunable steric and electronic properties.
27-30 As part of the pincer ligand family, examples of bis(phosphino)boryl ligands (
RPBP) have been designed and synthesized by the Nozaki and Yamashita groups,
31-33 and later, (
RPBP) ligands were studied with transition- metals such as Os, Ir, Pt, Ru, Rh, Pd and Co.
34-45 Nickel complexes with
tBuPBP ligands have been isolated and reported to be active for olefin hydrogenation and CO
2 reduction.
46-49 In DGGLWLRQ^^H[SHULPHQWDO^HYLGHQFH^KDV^EHHQ^UHSRUWHG^IRU^WKH^IRUPDWLRQ^RI^D^ı-ERUDQH^^^
2-B– H)Ni(0) species from the reaction of (
tBuPBP)NiH with 1,5-cyclooctadiene, which suggests that the hydride ligand is capable of migration from the Ni center to the boron center (Figure 8).
505HFHQWO\^^WKH^1R]DNL^JURXS^KDV^V\QWKHVL]HG^D^ELGHQWDWH^1L^^^^ı-borane complex {(^
2-B– H/P)Ni} and demonstrated its application in catalytic polymerization of ethylene for which the (^
2-B–H/P)Ni complex behaves as a masked Ni(II) boryl hydride that selectively produces linear polyethylene but not lower molecular weight ethylene oligomers (Figure 8).
51 These studies suggest that the installation of a non-innocent boryl-moiety in the ligand
Thomas Horstemeyer Docket No.: 222117-2220 structure offers unique reactivity, such as serving as a hydride shuttle, and could potentially alter the reaction pathway for catalytic processes. This example describes catalytic ethylene oligomerization reactions using a series of (
RPBP)NiBr (R = tBu, Ph, or Cy) catalyst precursors. Unique aspects of these catalytic processes include substantial activities for ethylene dimerization with an Al-based or Lewis acid co-catalysts, tunable selectivity for ethylene dimerization versus oligomerization based on ligand structure and co-catalyst identity, and a proposed catalytic reaction pathway that involves a non-innocent boron center on the ligand moiety and does not involve a Ni–H or Ni–alkyl intermediate, which we believe is a unique mechanism for olefin coupling processes. Results and Discussion Initial screening for ethylene dimerization. During the initial screening via in situ
1H NMR spectroscopy, (
tBuPBP)NiOAc (1), which was synthesized from (
tBuPBP)NiMe and CO
2,
49 was found to catalyze slow dimerization of ethylene to form 1-butene without a co- catalyst at 90 °C using C
6D
6 as the solvent (Table 1, entry 1). To test if the acetate group is required for the reaction, (
tBuPBP)NiBr (2) was used, and no peaks associated with the formation of butenes were observed in the
spectra (Table 1, entry 2). However, when using complex 2 in the presence of AgBF
4 as an additive for bromide abstraction, the ethylene dimerization reaction was achieved even at a lower temperature (60 °C) with ~75% selectivity for 1-butene (Table 1, entry 3). In an effort to achieve an in situ Br/OAc metathesis reaction to form complex 1, both TlOAc and AgOAc were examined as the additive for the ethylene dimerization reaction using complex 2 (Table 1, entry 4). The reaction with TlOAc after 2 days provided < 1 TO (turnover) of 1-butene (Table 1, entry 5). Based on these results, it can be concluded that the OAc group is likely not essential for the ethylene dimerization, and we speculated that cationic [(
tBuPBP)Ni]BF
4, formed through bromide abstraction from 2 with AgBF
4, is likely the active species for the ethylene dimerization reaction. Although we were unable to isolate the cationic complex [(
tBuPBP)Ni][BF
4], a crystal structure of [(
tBuPBP)Ni(OH
2)][BF
4] was obtained, which likely formed during the month-long crystal growing period in an insufficiently dried solvent. Next, different silver and sodium salts were tested as additives (see Supporting Information, Section 2), and only AgBF
4, AgSbF
6, AgBAr
F and NaBAr
F were found to provide active catalysts for ethylene dimerization in the presence of complex 2 (Table 1,
Thomas Horstemeyer Docket No.: 222117-2220 entries 3, 6–8). Control experiments using other Ni precursors such as (DME)NiCl
2, NiCl
2 and Ni(OAc)
2 with and without AgBF
4 showed no activity for ethylene dimerization (Figure 9A), which suggests that the
tBuPBP ligand is important for the dimerization reaction, leading us to speculate about a possible cooperative role for the Ni and B centers in the catalytic mechanism (see below for more discussion on this point). The Ni(II) complex (
PhPBP)NiBr (3) was synthesized and tested for ethylene dimerization, and we found that using 3 as a catalyst precursor yielded butenes at room temperature, but the reaction was less selective for 1-butene (Table 1, entries 9–11). It is possible that changing the tBu group to a less sterically hindered Ph group on the PBP moiety favors the coordination of 1-butene, which might provide access to a more facile isomerization of 1-butene to 2-butenes compared to the Ni catalyst coordinated by the
tBuPBP ligand (see below for more discussion and experimental results supporting this suggestion). Propylene was also tested as the substrate using complexes 1–3 in the presence of additives (i.e., AgBF
4^^0$2^^^KRZHYHU^^QR^UHDFWLRQ^ZDV^REVHUYHG^EDVHG^RQ^WKH^in situ
NMR studies (Figure 9B). However, a mixture of propylene and ethylene resulted in the formation of higher olefins with an odd number of carbon atoms along with products from ethylene oligomerization. These results indicate the likelihood of a Ni-catalyzed coupling reaction between ethylene and propylene, which also indicates that the coupling of ethylene and other D-olefins, such as 1-butene, is possible. Thus, the Ni-catalysis is selective toward homo- ethylene coupling or ethylene/D-olefin coupling but is less reactive for the coupling of two D- olefins. Table 1. Initial attempts for ethylene dimerization using (
RPBP)Ni complexes.
a
Ni Time Temp. TOF C
4 b 1-butene 2-butenes (TOs) Entry Additive complex (min) (°C) (s
í^) (TOs) trans cis 1 1 none 1440 90 3×10
í^ 2.3 N.D. N.D. 2 2 none 240 60 N.D.
c N.D. N.D. N.D. 3 2 AgBF
4 240 60 1×10
í^ 1.1 0.24 0.12
Thomas Horstemeyer Docket No.: 222117-2220 2 AgOAc 1440 60 N.D. N.D. N.D. N.D. 2 TlOAc 2880 60 6×10
í^ 0.8 N.D. N.D. 2 NaBAr
F 240 60 9×10
í^ 0.5 0.42 0.36 2 AgBAr
F 240 60 2×10
í^ 1.3 0.61 0.63 2 AgSbF
6 30 r.t. 2×10
í^ 3.4 0.24 0.28 3 AgSbF
6 15 r.t. 1.6×10
í^ 3.48 6.75 4.420 3 AgBF
4 20 r.t. 1.6×10
í^ 4.92 8.48 5.981 3 AgBAr
F 30 r.t. 9×10
í^ 0.56 0.70 0.33
a Reaction conditions: (
R3%3^1L;^^^^^^^^PRO^^LQ^^^^^P/^&
6D
6, additive (1.0 equiv. relative to Ni pre- catalyst), 40 psig ethylene.
b TOF C
4 = mol
butenes·mol
Ni í^·s
í^.
c N.D. = not detected. Ethylene dimerization/oligomerization using aluminum co-catalyst. Alkylaluminum compounds have been commonly used as co-catalysts for homogeneous ethylene oligomerization reactions using ligated Ni halide catalyst precursors, which generally led to enhanced activities.
4,52-56 Therefore, different alkylaluminums were tested as co-catalysts for our (
RPBP)Ni catalysis (Table 2), and the resulting rates of ethylene dimerization are improved. Control experiments using (
RPBP)H free ligand, alkylaluminums without Ni, (DME)NiBr
2 with alkylaluminums, and (
RPBP)H free ligand with alkylaluminums, produce no butenes or only trace amounts of butenes.
10,57 When using complex 2 as the pre-catalyst in the presence of 10 equivalents of methylaluminoxane (MAO), ethylene oligomerization was achieved at room temperature with a 0.09(1) s
í^ turnover frequency (TOF) for butenes (Table 2, entry 1) and 88(2)% selectivity for 1-butene (among the C
4 products), which is ~900 times faster than the reaction using complex 2 with AgBF
4 (Table 1, entry 3). However, the reaction products only contain ~12 wt. % of butenes (C
4), and a range of linear and 2-ethyl brancheG^Į-olefins were observed from C
6 to C
20 (Figure 10). The identity of the Al co-catalyst influences overall catalyst activity and selectivity. For example, changing the alkylaluminum co-catalyst from MAO to EtAlCl
2 results in a higher TOF (2.0(1) s
í^) with an increased mass fraction of C
4 olefins (~83 wt. %), while the reaction selectivity changes toward 2-butenes (Table 2, entry 2). By lowering the concentration of Ni pre-catalyst 2, a faster TOF (13.2(3) s
í^) was observed with a slightly improved selectivity for 1-butene (Table 2, entry 3). Therefore, it is possible that the isomerization of 1-butene to 2-butene is a competing reaction with the ethylene dimerization/oligomerization process.
Thomas Horstemeyer Docket No.: 222117-2220 Different from using Ni pre-catalyst 2, mixing pre-catalyst 3 with MAO gave an overall slower reaction with increased selectivity toward C
4 products (Table 2, entry 4). Using Et
2AlCl with 3 gave a slightly faster reaction (0.18(2) s
í^) while remaining selective for 1-butene (Table 2, entry 5), while the use of EtAlCl
2 with complex 3 significantly enhanced the TOF (2.5(3)s
í^) but changed the reaction selectivity towards 2-butenes (Table 2, entry 6). As shown in Table 2 entries 7–10, lowering the concentration of 3 improves the 1-butene selectivity as well as providing an enhanced TOF until the Ni loading is decreased WR^^^^^^^^PRO^^6LPLODUO\^^ZKHQ^XVLQJ^0$2^DV^WKH^DGGLWLYH^^GHFUHDVLQJ^WKH^1L^ORDGLQJ^IURP^ ^^^^^WR^^^^^^^^mol resulted in a higher TOF (Table 2, entry 4 vs 12). Lewis acidic AlCl
3 was also used as the co-catalyst with Ni pre-catalyst 3, and gave ethylene dimerization to form 1- butene with a TOF = 0.14(0) s
í^ (Table 2 entry 13). However, large amounts of Friedel– Crafts products from the reaction between toluene and ethylene/butenes were observed based on the GC-MS analysis. Therefore, due to the side reactions, the actual amount of C
4 products (i.e., butenes) produced under this condition is low (8 wt. %) compared to the total consumption of ethylene. The Ni pre-catalyst (
CyPBP)NiBr (4) has also been tested with MAO as an additive (Table 2, entry 14), which proved to be selective for 1-butene, but also gave 1-hexene, 2-ethyl-1-butene and 3-methyl-1-pentene as side products (Figure 10). Table 2. Screening of aluminum co-catalyst and loading of Ni pre-catalyst on ethylene oligomerization.
a
Ni Loading TOF C
4 b C Į-C /C ȕ-C
4/C
4 (%) Entry
a P
RO^ Additive 4 4 4 complex
^^ (s
í^) wt% (%) trans Cis 1
c 2 9.05 MAO 0.09(1) 12 88(2) 4(1) 7(1) 2
c 2 9.05 EtAlCl
2 2.0(1) 83 14(0) 56(0) 31(0) 3
c 2 0.905 EtAlCl
2 13.2(3) 91 46(6) 32(4) 23(2) 4 3 9.05 MAO 0.037(3) 80 88(2) 6(1) 6(1) 5 3 9.05 Et
2AlCl 0.18(2) 95 79(2) 11(1) 10(1) 6 3 9.05 EtAlCl
2 2.5(3) 90 16(1) 50(2) 35(2) 7 3 1.81 EtAlCl
2 3.7(1) 92 30(0) 41(1) 30(0) 8 3 0.905 EtAlCl
2 10.7(2) 94 30(0) 40(0) 31(0)
Thomas Horstemeyer Docket No.: 222117-2220 3 0.453 EtAlCl
2 18.1(6) 92 35(3) 38(2) 28(1)0 3 0.181 EtAlCl
2 3(1) 92 83(2) 10(1) 8(1)1 3 0.905 Et
3Al 0.20(2) 92 94(1) 4(1) 2(0)2 3 0.905 MAO 0.18(1) 94 95(0) 3(0) 2(0)3
d 3 0.905 AlCl
3 0.14(0) 8 90(2) 7(1) 3(1)4 4 0.905 MAO 2.7(2) 92 97(0) 2(0) 1(0)
a Reaction conditions: (
RPBP)NiBr ^^^^^^^^^^^^^^^^^^^^^^^^^^^DQG^^^^^^^^PRO^^^DGGLWLYH^^^^^HTXLY^^ relative to Ni pre-FDWDO\VW^^^XVLQJ^WROXHQH^DV^WKH^VROYHQW^^^^P/^WRWDO^IRU^HDFK^UHDFWLRQ^^^HWK\OHQH^ pressure was maintained at 200 psig using a Parr gas burette system. The total consumption of ethylene was measured based on the pressure change of the gas burette and used to calculate the weight percent of butenes in all reacted ethylene (C
4 wt. %). The reactions were performed at room WHPSHUDWXUH^^KRZHYHU^^WKH^DFWXDO^UHDFWLRQ^WHPSHUDWXUH^ZDV^unknown due to the exothermic nature of the reaction. Standard deviations were calculated from at least three independent experiments.
b TOF C
4 = mol
butenes·mol
Ni í^·s
í^.
c Longer chain products were detected.
d Friedel–Crafts products from the reaction between toluene and ethylene/butenes were observed. Effects of alkylating reagent and Lewis acid. To further understand the role of the alkylaluminum co-catalyst, different alkylating reagents were tested with the presence of Ni pre-catalyst 2 and 3, as shown in Table 3 entries 1–7. In all cases, no or only trace amounts of butenes (< 1 TO) were observed under the reaction conditions. Among these, the reaction of the Ni bromide complex 2 with Grignard reagent has been reported to form a stable (
tBuPBP)NiMe complex.
50 NaBH
4, a common hydride source used in the ethylene dimerization reaction,
2,58 was also tested and gave no production of butenes upon combination with complex 3 (Table 3, entry 8). Therefore, we believe the ethylene dimerization and oligomerization reactions are not initiated by Ni–alkyl/hydride species such those proposed in the Cossee-Arlman type mechanism (see Introduction). Since AlCl
3 with Ni pre-catalyst 3 was found to be active for the dimerization of ethylene, other Lewis acids such as BPh
3, BBr
3, and BF
3·OEt
2 were tested as an additive for the reaction (Table 3, entries 9–11). Among the results, BBr
3 with complex 3 showed activity for the production of 1-butene (TOF = 0.0013 s
í^), while using BF
3·OEt
2 as an additive gave a much faster ethylene dimerization with a TOF of 0.23(8) s
í^. The observation that Lewis acids without any hydride or alkyl sources (such as AlCl
3, BF
3, BBr
3) initiate the (
RPBP)Ni catalyzed ethylene dimerization is consistent with our proposal that the catalytic ethylene oligomerization reaction is not likely initiated by a Ni–alkyl/hydride species.
Thomas Horstemeyer Docket No.: 222117-2220 Table 3. Alkylating reagents and Lewis acids.
a
a Ni TOF C
4 b C
4/C
n Į-C
4/C
4 ȕ-C
4/C
4 (%) Entry Additive complex (s
í^) (%) (%) trans Cis 1 2 EtMgBr N.D. – N.D. N.D. N.D. 2 2 MeMgBr N.D. – N.D. N.D. N.D. 3 2 MeLi N.D. – N.D. N.D. N.D. 4 2 Me
2Mg N.D. – N.D. N.D. N.D. 5
c 3 EtMgBr trace – trace trace Trace 6 3 MeLi N.D. – N.D. N.D. N.D. 7 3 Me
2Mg N.D. – N.D. N.D. N.D. 8 3 NaBH
4 N.D. – N.D. N.D. N.D. 9
c,d 3 BPh
3 trace – trace trace Trace 10
d 3 BBr
3 0.0013 > 99 86 10 4 11
d 3 BF
3·OEt 0.23(8) 95(1) 80(0) 10(1) 10(0) a Reaction conditions: (
R3%3^1L%U^^^^^^^^PRO^^^DGGLWLYH^^^^^HTXLY^^WR^1L^SUH-FDWDO\VW^^^ XVLQJ^WROXHQH^DV^WKH^VROYHQW^^^^P/^WRWDO^IRU^HDFK^UHDFWLRQ^^^HWK\OHQH^SUHVVXUH^ZDV^ maintained at 200 psig using the Parr gas burette system. The reactions were performed at URRP^WHPSHUDWXUH^^KRZHYHU^^WKH^DFWXDO^Ueaction temperature was unknown due to the e
xothermic nature of the reaction. The mol% of butenes in all observed olefins (C 4/Cn) was determined by GC-MS. Standard deviations were calculated from at least three independent experiments.
b TOF C
4 = mol
butenes·mol
Ni í^·s
í^ c The observed amounts of products were less than 1 TO.
d 8VLQJ^^^^^^^^PRO^RI^1L^SUH-catalyst. Optimization of reaction parameters. Different reaction parameters such as Al/Ni ratio, Ni pre-catalyst loading, and ethylene pressure were optimized using complexes 2, 3, and 4 with MAO or EtAlCl
2 as shown in Table 4. We found that in general the TOF of butenes increases with the Al/Ni ratio (Table 4, entry 1 vs 2, 3 vs 4, 6 vs 7, 10 vs 11, 13 vs 14, 15 vs 16, 18 vs 19, 20 vs 21, 24 vs 25) as well as the dilution of the Ni pre-catalyst loading (Table 4, entry 2 vs 3, 7 vs 9, 14 vs 15, 19 vs 20 vs 24). The reaction is exothermic,
Thomas Horstemeyer Docket No.: 222117-2220 as the temperature rises upon addition of ethylene gas. Therefore, a set of experiments was performed with external cooling of the VCO steel reactor using an ice bath, which resulted in a slightly faster rate and better selectivity for 1-butene compared to the reaction at room temperature without cooling (Table 4, entry 7 vs 8). This suggests that higher reaction temperatures might not be beneficial for the reaction and, instead, could potentially lead to faster isomerization of 1-butene to 2-butenes, as well as possible decomposition of the active Ni species. Decreasing the loading of Ni pre-catalyst also generates less heat during the reaction, which could partially rationalize the increase in TOF when diluting the Ni pre- catalyst. When using EtAlCl
2 as the co-catalyst, increasing the ethylene pressure resulted in better selectivity for 1-butene (Table 4, entry 11 vs 12, 23 vs 24, 25 vs 26), while using MAO gave an opposite trend (Table 4, entry 4 vs 5, 16 vs 17). The difference in selectivity based on ethylene pressure is potentially rationalized by competition between ethylene dimerization, 1-butene to 2-butenes isomerization, and dimerization/oligomerization of butene upon reaction with ethylene. Using the more C
4 selective co-catalyst (i.e., EtAlCl
2), higher ethylene pressure suppresses 1-butene isomerization, while with the less C
4 selective co-catalyst (i.e., MAO), higher ethylene pressure favors the potential dimerization/oligomerization of butene with ethylene that might consume 1-butene and 2- butene at different rates with 1-butene being converted to higher olefins more rapidly than 2- butenes, thus decreasing the 1-butene to 2-butenes ratio. For all tested conditions, complex 2 with 1000 equivalents of EtAlCl
2 under 600 psig of ethylene, gave the fastest reaction which was selective for 1-butene with a TOF of 33(2) s
í^ and 87(0)% selectivity (Table 4, entry 12). Whereas, complex 3 under the same conditions achieved the best overall TOF of butenes (274(34) s
í^), but only 41(1)% selectivity for 1-butene (Table 4, entry 26).
Thomas Horstemeyer Docket No.: 222117-2220 Table 4. Effect of different reaction parameters on ethylene dimerization with (
RPBP)NiBr with alkylaluminum.
a
a Loading C2H4 Al/Ni TOF C4 Į-C4/C4 C4/Cn TOF C6 Entry [Ni] [Al] ^^PRO^ (psig) ratio (s
í^) (%) (%) (s
í^) 1
c 2 9.05 200 MAO 1 0.0012(1) 64(3) 20(2) 0.0004(1) 2
c 2 9.05 200 MAO 10 0.09(1) 88(2) 9(1) 0.10(1) 3
c 2 0.905 200 MAO 10 0.52(1) 98(0) 21(0) 0.27(1) 4
c 2 0.905 200 MAO 1000 2.2(2) 93(0) 6(1) 3.0(5) 5
c 2 0.905 600 MAO 1000 9(2) 80(1) 7(0) 10(3) 6
c 2 9.05 200 EtAlCl
2 1 0.023(2) 94(1) 28(2) 0.008(0) 7
c 2 9.05 200 EtAlCl
2 10 2.0(1) 14(0) 86(1) 0.29(2) 8
c,d 2 9.05 200 EtAlCl
2 10 2.8(5) 21(0) 85(2) 0.36(1) 9
c 2 0.905 200 EtAlCl
2 10 13(0) 46(6) 89(1) 0.97(6) 10
c 2 0.453 200 EtAlCl2 10 1.3(2) 89(1) 47(2) 0.30(5) 11
c,e 2 0.453 200 EtAlCl
2 1000 45(1) 48(0) 92(0) 2.1(1) 12
c,e 2 0.453 600 EtAlCl
2 1000 33(2) 87(0) 94(0) 0.8(1) 13 3 9.05 200 MAO 1 0.003(0) 93(0) – N.D. 14 3 9.05 200 MAO 10 0.037(3) 88(2) >98 0.0003 15 3 0.905 200 MAO 10 0.18(1) 95(0) 96(0) 0.0003(0) 16 3 0.905 200 MAO 1000 34(3) 16(0) 89(1) 3.7(2) 17 3 0.905 600 MAO 1000 66(4) 11(0) 69(2) 23(1) 18 3 9.05 200 EtAlCl
2 1 0.24(5) 69(10) 96(0) 0.01(0) 19 3 9.05 200 EtAlCl
2 10 2.5(3) 16(1) 81(1) 0.46(8) 20 3 0.905 200 EtAlCl
2 10 10.7(2) 30(0) 90(0) 1.1(1) 21 3 0.905 200 EtAlCl
2 100 27(5) 20(1) 84(2) 4.2(6) 22
e 3 0.905 600 EtAlCl
2 1000 110(13) 22(1) 85(2) 15(4) 23 3 0.453 100 EtAlCl
2 10 5.4(1) 22(1) 85(1) 0.8(0) 24 3 0.453 200 EtAlCl
2 10 18.1(6) 35(3) 92(1) 1.3(1) 25
e 3 0.453 200 EtAlCl
2 1000 115(17) 18(1) 91(1) 9(2) 26
e 3 0.453 600 EtAlCl
2 1000 274(34) 41(1) 88(3) 30(3) 27 4 0.905 200 MAO 10 2.7(2) 97(0) 90(1) 0.29(5)
Thomas Horstemeyer Docket No.: 222117-2220 4 0.905 200 MAO 1000 22(1) 33(0) 41(3) 19(2) 4 0.905 200 EtAlCl
2 10 14(1) 60(4) 83(2) 2.5(5) 4 0.905 200 EtAlCl
2 1000 20(2) 40(3) 94(0) 0.9(1)
a Reaction conditions: (
R3%3^1L%U^^^^^^^^^^^^^^DQG^^^^^^^^PRO^^^DGGLWLYH^^^^^^^^^^^^^DQG^^^^^^HTXLY^^ to Ni pre-FDWDO\VW^^^XVLQJ^WROXHQH^DV^WKH^VROYHQW^^^^P/^WRWDO^IRU^HDFK^UHDFWLRQ^^^HWK\OHQH^SUHVVXUH^ZDV^ maintained at 100, 200 or 600 psig using the Parr gas burette system. The reactions are performed at room temperDWXUH^^KRZHYHU^^WKH^DFWXDO^UHDFWLRQ^WHPSHUDWXUH^LV^XQNQRZQ^GXH^WR^WKH^H[RWKHUPLF^QDWXUH^ of the reaction. The mol% of 1-EXWHQH^LQ^EXWHQHV^^Į-C
4/C
4), and butenes in all observed olefins (C
4/C
n) were determined by GC-MS. N.D. = not detected. Standard deviations are calculated from at least three independent experiments.
b TOF C
4 = mol
butenes·mol
Ni í^·s
í^ c Longer chain products were detected.
d The VCO reactor was cooled with an ice bath during the reaction.
e Reaction was monitored after 10 min. Comparison of previously reported Ni catalysts. Table 5 compares selected results of our newly reported catalysis with previously reported homogeneous Ni catalysts which demonstrated activity for ethylene dimerization.
2,4,55-56,59-65 Although a direct comparison of previously reported catalysts is not possible since the reactions were performed under different conditions (e.g., pressure, temperature, Ni catalyst concentration, Al/Ni ratio, etc.), the comparative data provide some reasonable comparison points. The activities given in Table 5 were all converted into a commonly used unit g
oligomers·mol
Ni í^·h
í^ for each catalytic system. The overall TOFs given in Table 5 were calculated based on ethylene consumption, for which TOF = activity/(molar mass of C
2H
4) with a unit
general, most of the reported highly active Ni catalysts are supported by SHOP-type and related phosphine-sulfur-, phosphine-, nitrogen-based ligand structures. In addition to the ethylene polymerization reaction reported by the Nozaki group,
51 there are only a limited number of ligand structures with a central boron center.
66 As outlined in Table 5, the new
RPBP ligated Ni complexes reported in this work exhibit relatively high activities for the ethylene dimerization reaction, which motivated us to better understand the reaction pathway (see below). Table 5. Comparison of previously reported homogeneous Ni catalysts for ethylene dimerization to our newly reported PBP-Ni catalysis.
a Ligand Activity
a TOFethylene
b Į-C4/C4 C4/Cn Temp. co-catalyst
í^ ref type g/(mol
Ni·h) (s ) (%) (%) (°C)
Thomas Horstemeyer Docket No.: 222117-2220 (P,P) EtAlCl
2 2.4 × 10
8 2377 35 82 45 (
55) (O,N,S) MAO 1.4 × 10
8 1411 16 90 0 (
56) (N,N) Et
3Al
2Cl
3 4.6 × 10
7 460 92 88 r.t. (
59) (N,N,N) Et
2AlCl/PPh
3 4.0 × 10
7 391 12 92 20 (
60) (N,N) MAO 1.9 × 10
7 190 56 90 35 (
61) (P,O) None 1.9 × 10
7 183 99 85 40 (
67) (N,N,O) MAO 1.2 × 10
7 119 18 83 45 (
62)
(P,N) EtAlCl 2 9.1 × 10 6 90 23 98 40 ( 63 ) (N,O) Et
2AlCl 6.6 × 10
6 65 100 100 30 (
64) (N,N) Et
2AlCl 4.7 × 10
6 46 > 99 77 45 (
65) (
tBuP,B,P) EtAlCl
2 6.9 × 10
6 68 87 94 r.t. this (
PhP,B,P) EtAlCl
2 6.5 × 10
7 640 41 89 r.t. work a Most of the catalysts activities in this table were originally reported in g
oligomers·mol
Ni í^·h
í^, thus we converted all data to the same units for comparison.
b Based on ethylene consumption, for which TOF = activity/(28.05 g/mol) with the unit of mol
ethylene·mol
Ni í^·s
í^. Isomerization of 1-butene. A set of experiments using 1-butene as the only substrate with EtAlCl
2 or MAO as the co-catalyst with and without Ni pre-catalyst 2 or 3 was performed (Figure 1). Similar to the reaction using propylene as a substrate, no dimerization or oligomerization products of butenes were found based on the GC-MS analysis. While both complex 2 and 3 were able to isomerize 1-butene to 2-butenes in the presence of EtAlCl
2 or MAO, control experiments using only EtAlCl
2 or MAO showed much slower rates of isomerization of 1-butene to 2-butenes. Using the Ni pre-catalyst 3 approximately 10-fold faster isomerization of 1-butene to 2-butenes was observed compared to pre-catalyst 2 under the conditions using EtAlCl
2, which is consistent with the observed ligand effect on 1- vs 2- butene selectivity of the ethylene dimerization reactions (see Table 1, and Table 4, entry 6 vs 18, 9 vs 21, 10 vs 24, 11 vs 25, 12 vs 26). As noted above, this ligand effect (i.e., 2-butenes vs. 1-butene selectivity as a function of identity of PBP ligand) can be rationalized by the presence of a more sterically hindered
tBu group in complex 2 inhibiting 1-butene coordination, and thus retarding the rate of 1-butene isomerization. In addition, using EtAlCl
2 with and without Ni pre-catalyst gave a much faster isomerization compared to MAO, which is also consistent with the observed difference in 1- vs 2-butene selectivity when using EtAlCl
2 or MAO as additive (see Table 4, entries 2 vs 7, 3 vs 9, 13 vs 18, 14 vs 19, 15 vs
Thomas Horstemeyer Docket No.: 222117-2220 DFT analysis on the reaction mechanism. The aforementioned experimental data point to a mechanism for which the [(
RPBP)Ni]
+ fragment plays a fundamental role in the dimerization of ethylene to yield 1-butene. Indeed, control experiments revealed the participation of both the PBP ligand and nickel in the process, and stoichiometric experiments ruled out the likely involvement of nickel acetate, hydride, or alkyl species. Therefore, we conducted DFT studies using cationic complex 5, produced from the reaction between bromide species 2 and a halide abstractor (e.g., AgBF
4, NaBAr
F, AgBAr
F, etc.). Calculations were carried out at the PBE0/def2TZVP/def2QZVP level of theory, including Grimme’s D3 dispersion correction (PBE0-D3, see SI for information and references), using 5 and ethylene as the energy reference. Scheme 3, Figure 11, illustrates halide abstraction from complex 2 to give cationic complex 5. Coordination of one ethylene molecule to the vacant position of [(
tBuPBP)Ni]
+ (5) to give [(
tBu3%3^1L^^
2-C
2H
4)]
+ (5·C
2H
4) LV^LVRHQHUJHWLF^^í^^^^^NFDO^PRO
-1) to the reactants. From this point, several mechanistic scenarios were considered, most of which afforded kinetic barriers too energy-demanding to overcome experimentally (energy profiles for the energetically inaccessible pathways can be found in the Supporting Information). Activation of a C–+^ERQG^RI^ERXQG^HWK\OHQH^^ǻG > 50 kcal mol
í^) of 5·C
2H
4 gave Ni–vinyl and B–H fragments in a less thermodynamically stable geometry than the initial cationic Ni–HWK\OHQH^ʌ^ complex (23.4 kcal mol
í^ difference). Including weakly coordinating anions such as BF
4 í in the calculations led to even higher Gibbs free energy values. The addition of a free ethylene molecule to the coordinated ethylene of 5·C2H4 was also computed, based on the study by Bernardi, Bottoni et al.
21 This resulted in the desired 5·1-butene FRPSOH[^^í^^^^^NFDO^PRO
í^), yet at the expense of very high energy transition states.
68 Exploratory calculations involving [2+2] cycloaddition pathways did not lead to chemically meaningful results. Finally, dissociation of one of the phosphine ligands or coordination of the ethylene molecule across the Ni–B bond gave energy barriers above 30 kcal mol
í^ along with thermodynamically unstable products. However, coordination of a second ethylene molecule to 5·C2H4 opened the door to a new ethylene dimerization mechanism involving participation of the PBP ligand. Figure 2 shows a calculated pathway for (
RPBP)Ni-mediated positioning of two ethylene molecules for subsequent C–C coupling. Ethylene binding to give complex 5·(C
2H
4)
2 is thermodynamically unfavorable (18.5 kcal mol
í^ higher than 5·C
2H
4), as depicted in Figure 2. This is in line with our previous studies on H
2 activation by neutral,
Thomas Horstemeyer Docket No.: 222117-2220 square planar Ni(II) complexes,
50,69 for which the filled d
z 2 orbital on nickel gave rise to weak ı-H
2 complexes.
70 Indeed, 5·(C2H4)2 exhibits very little C=C bond elongation upon binding (1.36 Å vs 1.33 Å in free ethylene). Nonetheless, molecular orbital analysis of ethylene and 5·C
2H
4 (Figure 3) point to potential orbital overlap involving the PBP ligand {HOMO (5·C2H4) Æ LUMO (ethylene)} that can lead to ethylene functionalization. In fact, this second ethylene molecule binds across the Ni–B bond in transition state TS1 (23.2 kcal mol
í^) to form a 4-membered borametallacycle, simultaneously promoting dissociation of one of the phosphine ligands from the metal center, as observed in the product 6 (Figure 2). Complex 5 is 16.2 kcal mol
í^^above the reactants, which suggests the formation of 5 is possibly reversible. However, the rest of the kinetic barriers are lower than TS1, and the high thermodynamic stability of the product makes the overall process energetically downhill and favorable towards the formation of the experimentally observed 1-butene (see below). The calculated phosphine dissociation is probably due to steric clash between the ethylene moieties and the tert-butyl substituents on the phosphorus atom. In fact, both ethylene ligands in 6 are oriented towards the space previously occupied by the phosphine ligand (Figure 2, inset). The short C···C distance (2.37 Å) observed for the two closer carbon atoms suggests preorganization of both ethylene fragments for subsequent C–C coupling. The C–C bond formation between two ethylene ligands is calculated to proceed through TS2 (17.1 kcal mol
í^), located only 0.9 kcal mol
í^ higher than complex 6 (Figure 4). The next intermediate after TS2 (species 7, 13.9 kcal mol
í^) contains a six-membered B–C
į–C
Ȗ–C
ȕ–C
Į–Ni ring, with C–C distances ranging from 1.50 to 1.67 Å. Although the distance arrangement might suggest some butadiene character, these C–C bonds are longer than those observed in 1,3- butadiene (1.34–1.45 Å).
71 From complex 7, numerous hydrogen atom migrations have been explored to form either B–H or new C–H bonds, giving too energy demandiQJ^^ǻG > 30 kcal mol
í^) kinetic barriers. However, the C
ȕ^atom can orient one of its hydrogen atoms closer to the metal center with minimal energy cost (TS3 = 12.8 kcal mol
í^), in order to achieve a VXLWDEOH^VWUXFWXUH^IRU^D^ȕ-hydride elimination step. The outcome of this rearrangement is complex 8, which exhibits an agostic interaction
72 through the C
ȕ–H bond (Ni–H = 1.78 Å, Ni–C = 2.11 Å, Ni–H–C = 89.2°), located trans to the bound phosphine ligand. Although this complex is rather low in Gibbs free energy (7.9 kcal mol
í^), we found a different, more energy-demanding isomer (8', 19.7 kcal mol
í^) where the C
ȕ–H bond and the bound phosphine are in a cis orientation, and the 3c-2e interaction exhibits a much shorter Ni–H bond (1.55 Å), with similar Ni–C (2.11 Å) and Ni–H–C (96.9°) metrics to those observed for
Thomas Horstemeyer Docket No.: 222117-2220 7. Complex 8' SURFHHGV^WR^D^ȕ-H elimination transition state (TS4) with a free energy of activation of only 0.3 kcal/mol. The geometry of 8' is very similar to that observed for TS4 (early transition state), which might explain why the firsW^ȕ-hydride elimination step is only 0.3 kcal mol
í^ higher in energy (Figure 5). After TS4, intermediate 9 (12.4 kcal mol
í^) contains the newly formed C=C double bond (C=C distance = 1.36 Å) bound to nickel, along with coordination of one of the phosphines and the new hydride ligand. In addition, the fourth Ni-coordination position LV^VWDELOL]HG^E\^D^ZHDN^ı^LQWHUDFWLRQ^ZLWK^WKH^%–C
į bond (B–Ni = 2.76 Å C–Ni = 2.48 Å). Although one might think that 1-butene is practically formed, exploratory calculations involving hydride transfer to C
į or B to release the experimentally observed product led to high (> 30 kcal mol
í^) energy barriers. Nevertheless, TS5 (11.6 kcal mol
í^) was found, which reveals the stretch of the B–C
Ni interaction along its imaginary frequency, giving rise to species 10 (10.8 kcal mol
í^). In this geometry, an agostic interaction through the C
į–H bond is observed (Ni–H = 1.88 Å, Ni–C = 2.28 Å, Ni–H–C = 95.5°) along with shorter Ni···C distances (ranging from 0.05 to 0.2 Å) for all the carbon atoms coming from the ethylene fragments. Next, hydride transfer to C
Į^occurs via TS6, located 15.6 kcal mol
í^ above the energy reference. This hydride transfer process leads to intermediate 11 (14.8 kcal mol
í^), which contains a new nickel-carbon bond (Ni–C
ȕ^= 1.89 Å) and two agostic interactions: the previous one observed for the C
į–H bond, and another for one of the C
Į–H bonds of the new CH
3 group. In a similar fashion to intermediates 8 and 8', isomer 11' was found, where both agostic interactions are replaced by two different ones: one C–H bond from one of the tert- butyl groups of the bound phosphine, and a C–H bond from C
Ȗ. This bonding arrangement is DJDLQ^VXLWDEOH^IRU^D^ȕ-hydride elimination step, which indeed proceeds through TS7, located only 0.6 kcal mol
í^ above 11'. This event leads to the formation of an internal double bond in the tetracarbon chain of complex 12 (10.4 kcal mol
í^). From this point, it seems reasonable that the hydride ligand can be transferred to C
į^to rationalize the formation of trans 2-butene. However, relaxed potential energy scan calculations revealed hydride transfer to C
Ȗ instead (i.e., formation of intermediate 11), probably due to its closer proximity and the relative stability of such geometry. Complex 12 features a nickel center with a T-shaped geometry for which the hydride ligand is pointing to the boryl fragment. Therefore, it needs to orbit around the metal in order to give 1-butene. This orbiting movement requires negligible energy (TS8, 10.6 kcal mol
í^) and places the hydride ligand close to C
ȕ (H···C
ȕ^= 2.53 Å, intermediate 13, Figure 6) for
Thomas Horstemeyer Docket No.: 222117-2220 subsequent transfer, which takes place via TS9 (14.6 kcal mol
í^). Interestingly, this transition state also involves the formation of the C
į=C
Ȗ double bond and the cleavage of the B–C
į bond, giving species 14. In this intermediate, the nickel atom adopts a distorted square planar geometry in which 1-butene is bound to nickel through the double bond and one agostic interaction. Thus, phosphine coordination can easily occur (TS10, 6.6 kcal mol
í^), displacing the C–H bond and regenerating the pincer scaffold in 5·1-butene ^í^^^^^NFDO^PRO
í^). Finally, regeneration of cationic complex 5 and dissociation of the 1-butene is the most stable step in WKH^HQWLUH^SURFHVV^^DV^H[SHFWHG^^í^^^^^NFDO^PRO
í^). This proposed mechanism highlights the role of the PBP ligand in the catalytic dimerization of ethylene. First, its tridentate nature allows the approach of one equivalent of ethylene to the vacant position of a square planar, cationic Ni(II) complex. Then, the boryl fragment facilitates coordination of a second ethylene molecule, and serves as an anchoring point for one of the ends of the tetracarbon chain, allowing hydrogen atom rearrangement throughout the entire cycle while keeping the substrate bound to the catalyst. Lastly, the hemilabile character of the phosphine groups on the pincer scaffold is instrumental for the development of the elementary steps in the cycle, since they can dissociate when needed to create a vacant position in the coordination sphere, which they can also stabilize by means of agostic interactions through the substituents on phosphorus. Summary and Conclusions We have demonstrated that
RPBP-Ni complexes are active catalysts for ethylene dimerization/oligomerization. Our studies revealed that the ethylene dimerization is generally selective for the formation of terminal 1-butene, and that the features of catalysis are dependent on ligand identity. The reactions proceed by using (
tBuPBP)NiOAc (1) without co- catalyst, as well as mixing (
RPBP)NiBr (2 or 3) with Ag
+ or Na
+ salts, alkylaluminum, or other Lewis acids (e.g., BF
3, BBr
3, and AlCl
3). The (
PhPBP)Ni complex 3 shows significant activity for the production of butenes with a TOF up to 274(34) mol
butenes·mol
Ni í^·s
í^ (41(1)% selective for 1-butene), while the (
tBuPBP)Ni complex 2 shows good selectivity for 1-butene with a TOF up to 33(2) mol
butenes·mol
Ni í^·s
í^ (87(0)% selective for 1-butene). Experimental evidence is consistent with the reaction likely being initiated by cationic [(
RPBP)Ni]
+ species instead of Ni–alkyl/hydride complexes.
Thomas Horstemeyer Docket No.: 222117-2220 Experimental Section General information. All reactions were performed under a dinitrogen or argon atmosphere using Schlenk line techniques or inside a dinitrogen filled glovebox unless specified otherwise. GC-MS was performed using a Shimadzu GCMS-QP2020 NX with a 30 m × 0.25 mm Rt-Q-Bond capillary column with 8 μm film thickness and a 30 m × 0.25 mm Rxi-5ms capillary column with 0.25 μm film thickness using electron impact ionization method. All NMR reactions were performed using Wilmad medium wall precision low pressure/vacuum (LPV) NMR tubes and pressurized with ethylene or propylene using a high- pressure line. Toluene was dried using a sodium-benzophenone/ketyl still under a dinitrogen atmosphere and stored inside a glovebox. Tetrahydrofuran and diethyl ether were dried via a potassium-benzophenone/ketyl still under a dinitrogen atmosphere and stored over activated 4Å molecular sieves inside a glovebox. Benzene, pentane, and methylene chloride were dried using a solvent purification system with activated alumina and stored under activated 3Å molecular sieves inside a dinitrogen filled glovebox. Hexanes was dried using 4Å molecular sieves. Toluene-d
8 and benzene-d
6 were dried and stored over activated 3Å molecular sieves inside a glovebox. All other chemicals were purchased from commercial sources and used as received. NMR spectra were recorded on Varian VNMRS 600 MHz or 500 MHz spectrometer or a Bruker Avance III 800 MHz spectrometer. All reported chemical shifts were referenced to residual
1H resonances (
1H NMR) or
13C{
1H} resonances (
13C{
1H} NMR).
1H NMR: benzene-d
6 ^^^^^SSP^^WROXHQH-d
87.09 ppm.
13C NMR: benzene-d
6 ^^^^^^SSP^^WROXHQH-d
8 137.5 ppm.
73 The
19F 105^VSHFWUD^ZHUH^UHIHUHQFHG^WR^KH[DIOXRUREHQ]HQH^į^í^^^^^^SSP^DV^ an external standard.
31P{
1H} NMR spectra were referenced to H
3PO
4 į^^^^^SSP^DV^DQ^ external standard. Elemental analyses were performed by the University of Virginia Chemistry Department Elemental Analysis Facility. General procedure for in Situ
1H NMR Studies of ethylene dimerization. Described here is a representative procedure for our NMR studies. Inside a dry dinitrogen filled glovebox, a stock solution of internal standard hexamethyldisiOR[DQH^^+0'62^^^^^^/^^ 0.0471 mmol) in 10 mL of benzene-d
6 was made using a volumetric flask. A stock solution of Ni pre-FDWDO\VW^^^^^^^^PRO^^LQ^^^P/^RI^WKH^+0'62^EHQ]HQH-d
6 solution was made to ensure reproducible concentration of the Ni complex (9.05 mmol^/^^^7KH^DGGLWLYH^^^^^^^^PRO^^^^ equiv. relative to Ni pre-catalyst) was added to the stock solution of Ni pre-catalyst. After
Thomas Horstemeyer Docket No.: 222117-2220 stirring, 0.5 mL of the mixture was syringed into a medium-wall LPV NMR tubes. Then, the LPV NMR tubes were pressurized with 40 psig of ethylene. Quantitative
NMR experiments were performed using HMDSO as the internal standard. The LPV NMR tube was held at room temperature or heated in an oil bath at a specific temperature, then the integration changes of the 1-butene, trans- and cis-2-butene signals were measured at time intervals by experiments. General procedure for high-pressure reactions under constant ethylene pressure. All high-pressure reactions were performed using customized steel reactors (VCO) with a fixed volume (300 cm
3) high pressure gas burette system. The connection between reactor and the gas burette system was custom built with the function to place all metal tubing under vacuum to prevent air or moisture contamination of the VCO reactor. The following is a representative procedure for our high-pressure studies. The high-pressure gas burette system was evacuated and refilled with pure ethylene (99.9%, 3.0 PL) using a high-pressure line. Inside a dry dinitrogen filled glovebox, the Ni pre-FDWDO\VW^^^^^^^^PRO^^ZDV^SODFHG^LQ^WKH^ VCO reactor with a glass insert, followed by addition of dried toluene (1 mL total, the actual volume depends on the amount of additive used) and additives (equiv. relative to Ni pre- catalyst). When using lower Ni pre-catalyst loading, a stock solution of Ni pre-catalyst in dry toluene was made to ensure reproducible concentrations of Ni complex. Then the VCO reactor was sealed and connected to the high-pressure gas burette system prefilled with ethylene. The connection metal tubing was evacuated and then charged with ethylene, and this process was repeated three times. The output ethylene pressure was set to 200 psig (or 600 psig under some conditions). Then the valve connected to the VCO reactor was opened, and the pressure on the gas burette was recorded. After specific reaction time (10 or 20 min), the valve connected to the VCO reactor was closed and the pressure on the gas burette was recorded, followed by placing the VCO reactor into a dry ice/acetone bath. The pressure change of the gas burette was used to calculate ethylene consumption using the ideal gas law. After the reactor was sufficiently cooled, the top pressure was slowly released, followed by adding 1 mL of toluene (undried) to the reactor. For the conditions using 1000 equivalents of DON\ODOXPLQXP^^^^GURS^RI^ZDWHU^ZDV^DGGHG^^7KHQ^^^^^^/^RI^WHWUDK\GURIXUDQ^ZHUH^V\ULQJHG^ into the reactor as the standard for GC-MS analysis. Butenes were quantified using a Rt-Q- Bond column, and the remainder of the olefins was quantified using with a Rxi-5ms column. Synthesis and characterization of Ni complexes. (
tBuPBP)NiOAc (1),
49 and (
tBuPBP)NiBr (2),
50 and (
PhPBP)H
33 were synthesized based on published procedures.
Thomas Horstemeyer Docket No.: 222117-2220 (
PhPBP)NiBr (3). To a solution of (DME)NiBr
2 (240 mg, 0.778 mmol) in 15 mL of dry toluene under Ar atmosphere, a solution of (
PhPBP)H (400 mg, 0.778 mmol) and Et
3N ^^^^^^P/^^^^^^^^PPRO^^LQ^^^^P/^RI^GU\^WROXHQH^ZDV^FDQQXODWHG^VORZO\^DW^í^^^^&^^7KH^ reaction mixture was allowed to warm to room temperature slowly and stirred overnight. The solvent was removed in vacuo, then the solid residue was washed with cold pentane ^í^^^^&^^ 5 mL × 2). The resulting solid was extracted using dry toluene, and the solution was dried under vacuum to isolate the product as an orange-yellow solid that is sensitive to moisture and oxygen (390 mg, 78% isolated yield).
1H NMR (800 MHz, benzene-d
6^^į^^^^^^^GG^YW^^
1J
H,H = 7 Hz,
3J
H,H = 2 Hz, 8H), 7.15 (AA'XX' dd, partially overlapped with benzene-d
6, 2H), 7.01 – 6.96 (m, 12H), 6.90 (AA'XX' dd, J
AX = 7.7 Hz, J
AX' = 1.2 Hz, J
AA' = 0.4 Hz, J
XX' = 7.6 Hz, 2H), 4.00 (vt, N = 4.8 Hz, 4H, NCH
2P).
31P{
1H} NMR (243 MHz, benzene-d6^^į^^^^^^^^V^^
13C{
1H} NMR (201 MHz, benzene-d6^^į^ 139.2 (vt, N = 18 Hz), 133.7 (vt, N = 12 Hz), 132.7 (vt, N = 38 Hz), 130.4, 128.8 (vt, N = 9 Hz), 119.4, 109.7, 49.1 (vt, N = 44 Hz, PCH
2). Anal. Calcd for C
32H
28BBrN
2NiP
2^^&^^^^^^^^^ +^^^^^^^^1^^^^^^^^)RXQG^^&^^^^^^^^^+^^^^^^^^1^^^^^^^ (
CyPBP)NiBr (4). A solution of (
CyPBP)H ligand (500 mg, 0.928 mmol) in toluene (10 mL) and Et
31^^^^^^^^P/^^^^^^^PPRO^^DW^í^^^^&^ZDV^WUDQVIHUUHG^YLD^FDQQXOD^WR^D^ suspension of (DME)NiBr
2 (286.4 mg, 0.928 mmol) in toluene (10 mL) at the same temperature. The resulting suspension was allowed to warm to room temperature, and it was stirred at the same temperature for 18 h, after which the stirring was stopped, and the dark yellow solution decanted to a Schlenk flask by using a cannula with a double filter paper. The remaining solid was extracted with toluene (10 mL × 3), and the combined organic phase was evaporated under vacuum to give Ni–Br as a brown solid (578 mg, 0.854 mmol, 92% yield). X-Ray quality crystals can be obtained by diffusion of pentane into a toluene solution of 4.
1H NMR (400 MHz, benzene-d
6): į^7.18 (AA'XX' dd, partially overlapped with benzene-d
6, 2H, aromatic CH), 7.01 (AA'XX' dd, J
AX = 7.6 Hz, J
AX' = 1.3 Hz, J
AA' = 0.5 Hz, J
XX' = 7.6 Hz, 2H, aromatic CH), 3.41 (vt, N = 4.2 Hz, 4H, NCH
2P), 2.30 (m, 4 H, CH
2), 2.19
Thomas Horstemeyer Docket No.: 222117-2220 (quint vt,
3J
HH = 2.9 Hz, N = 24.6 Hz, 4H, CH-P), 1.80 (m, 4 H, CH
2), 1.70 (m, 4 H, CH
2), 1.59 (m, 12 H, CH
2), 1.36 (m, 4 H, CH
2), 1.22 (m, 4 H, CH
2), 1.08 (m, 8 H, CH
2).
31P{
1H} NMR (161 MHz, benzene-d
6) į 66.68 (s).
11B{
1H} NMR (128 MHz, benzene-d
6): į 40.3 (br s, boryl).
13C{
1H} NMR (100 MHz, benzene-d
6): į^139.7 (vt, N = 16 Hz, ligand aromatic C
q), 119.0 (ligand aromatic CH), 109.3 (ligand aromatic CH), 40.5 (vt, N = 37 Hz, NCH
2P), 33.9 (vt, N = 19. Hz, C
1), 29.2 (C
2, C
6), 28.8, 27.1 – 27.3 (m, C
3,C
5), 26.5 (C
4). Anal. Calcd. for C
32H
52BBrN
2NiP
2^^&^^^^^^^^^+^^^^^^^^1^^^^^^^^)RXQG^^&^^^^^^^^^+^^^^^^^^1^^^^^^^ References 1. 3LOODL^^6^^0^^^5DYLQGUDQDWKDQ^^0^^^6LYDUDP^^6^^^'LPHUL]DWLRQ^RI^HWK\OHQH^DQG^ propylene catalyzed by transition-metal complexes. Chem. Rev.1986, 86, 353-399. doi: 10.1021/cr00072a004 2. Olivier-%RXUELJRX^^+^^ %UHXLO^^3^^$^^5^^^0DJQD^^/^^^0LFKHO^^7^^^(VSDGD^3DVWRU^^0^^)^^^ Delcroix, D., Nickel Catalyzed Olefin Oligomerization and Dimerization. Chem. Rev. 2020, 120, 7919-7983. doi: 10.1021/acs.chemrev.0c00076 3. ,WWHO^^6^^'^^^-RKQVRQ^^/^^.^^^%URRNKDUW^^0^^^/DWH-Metal Catalysts for Ethylene Homo- and Copolymerization. Chem. Rev. 2000, 100, 1169-1204. doi: 10.1021/cr9804644 4. %HNPXNKDPHGRY^^*^^(^^^6XNKRY^^$^^9^^^.XFKNDHY^^$^^0^^^<DNKYDURY^^'^^*^^^1L- Based Complexes in Selective Ethylene Oligomerization Processes. Catalysts 2020, 10. doi: 10.3390/catal10050498 5. Breuil, P.-$^^5^^^0DJQD^^/^^^2OLYLHU-Bourbigou, H., Role of Homogeneous Catalysis in Oligomerization of Olefins : Focus on Selected Examples Based on Group 4 to Group 10 Transition Metal Complexes. Catal. Lett. 2015, 145, 173-192. doi: 10.1007/s10562-014- 1451-x 6. IHS Chemicals, Chemical economics handbook: linear alphaolefins, February 2020 7. =LHJOHU^^.^^^*HOOHUW^^+^^^+RO]NDPS^^(^^^:LONH^^*^^^(QWGHFNXQJ^GHV^1LFNHO^(IIHNWV^^ Brennst.-Chem. 1954, 35, 321. doi: 8. )LVFKHU^^.^^^-RQDV^^.^^^0LVEDFK^^3^^^6WDEED^^5^^^:LONH^^*^^^7KH^³1LFNHO^(IIHFW´^^ Angew. Chem. Int. Ed. 1973, 12, 943-953. doi: 10.1002/anie.197309431 9. McGuinness, D. S., Olefin Oligomerization via Metallacycles: Dimerization, Trimerization, Tetramerization, and Beyond. Chem. Rev.2011, 111, 2321-2341. doi: 10.1021/cr100217q
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Thomas Horstemeyer Docket No.: 222117-2220 21. %HUQDUGL^^)^^^%RWWRQL^^$^^^5RVVL^^,^^^$^')7^,QYHVWLJDWLRQ^RI^(WK\OHQH^'LPHUL]DWLRQ^ Catalyzed by Ni(0) Complexes. J. Am. Chem. Soc. 1998, 120, 7770-7775. doi: 10.1021/ja980604r 22. *UXEEV^^5^^+^^^0L\DVKLWD^^$^^^7KH^PHWDOODF\FORpentane–olefin interchange reaction. J. Chem. Soc., Chem. Commun. 1977, 864-865. doi: 10.1039/c39770000864 23. *UXEEV^^5^^+^^^0L\DVKLWD^^$^^^/LX^^0^-,^^0^^^%XUN^^3^^/^^^7KH^SUHSDUDWLRQ^DQG^ reactions of nickelocyclopentanes. J. Am. Chem. Soc. 1977, 99, 3863-3864. doi: 10.1021/ja00453a068 24. *UXEEV^^5^^+^^^0L\DVKLWD^^$^^^0HWDOODF\FORSHQWDQHV^DV^FDWDO\VWV^IRU^WKH^OLQHDU^DQG^ cyclodimerization of olefins. J. Am. Chem. Soc. 1978, 100, 7416-7418. doi: 10.1021/ja00491a051 25. *UXEEV^^5^^+^^^0L\DVKLWD^^$^^^7KH^UHODtionship between metallacyclopentanes and bis(olefin)-metal complexes. J. Am. Chem. Soc. 1978, 100, 1300-1302. doi: 10.1021/ja00472a050 26. *UXEEV^^5^^+^^^0L\DVKLWD^^$^^^/LX^^0^^^%XUN^^3^^^3UHSDUDWLRQ^DQG^UHDFWLRQV^RI^ phosphine nickelocyclopentanes. J. Am. Chem. Soc. 1978, 100, 2418-2425. doi: 10.1021/ja00476a026 27. *X^^6^^^1LHOVHQ^^5^^-^^^7D\ORU^^.^^+^^^)RUWPDQ^^*^^&^^^&KHQ^^-^^^'LFNLH^^'^^$^^^ *RGGDUG^^:^^$^^^*XQQRH^^7^^%^^^8VH^RI^/LJDQG^6WHULF^3URSHUWLHV^WR^&RQWURO^WKH^ Thermodynamics and Kinetics of Oxidative Addition and Reductive Elimination with Pincer- Ligated Rh Complexes. Organometallics 2020, 39, 1917-1933. doi: 10.1021/acs.organomet.0c00122 28. .RQJ^^)^^^*X^^6^^^/LX^^&^^^'LFNLH^^'^^$^^^=KDQJ^^6^^^*XQQRH^^7^^%^^^(IIHFWV^RI^ Additives on Catalytic Arene C–H Activation: Study of Rh Catalysts Supported by Bis- phosphine Pincer Ligands. Organometallics 2020, 39, 3918-3935. doi: 10.1021/acs.organomet.0c00623 29. *ROGEHUJ^^-^^0^^^:RQJ^^*^^:^^^%UDVWRZ^^.^^(^^^.DPLQVN\^^:^^^*ROGEHUJ^^.^^,^^^ Heinekey, D. M., The Importance of Steric Factors in Iridium Pincer Complexes. Organometallics 2015, 34, 753-762. doi: 10.1021/om501166w 30. $URUD^^9^^^1DUMLQDUL^^+^^^1DQGL^^3^^*^^^.XPDU^^$^^^5HFHQW^DGYDQFHV^LQ^SLQFHU–nickel catalyzed reactions. Dalton Trans. 2021, 50, 3394-3428. doi: 10.1039/d0dt03593a 31. 6HJDZD^^<^^^<DPDVKLWD^^0^^^1R]DNL^^.^^^%RU\OOLWKLXP^^,VRODWLRQ^^&KDUDFWHUL]DWLRQ^^ and Reactivity as a Boryl Anion. Science 2006, 314, 113. doi: 10.1126/science.1131914
Thomas Horstemeyer Docket No.: 222117-2220 32. 6HJDZD^^<^^^<DPDVKLWD^^0^^^1R]DNL^^.^^^6\QWKHVHV^RI^3%3^3LQFHU^,ULGLXP^&RPSOH[HV^^ A Supporting Boryl Ligand. J. Am. Chem. Soc. 2009, 131, 9201-9203. doi: 10.1021/ja9037092 33. 6HJDZD^^<^^^<DPDVKLWD^^0^^^1R]DNL^^.^^^'LSKHQ\OSKRVSKLQR- or Dicyclohexylphosphino-Tethered Boryl Pincer Ligands: Syntheses of PBP Iridium(III) Complexes and Their &RQYHUVLRQ^WR^,ULGLXPí(WK\OHQH^&RPSOH[HV^^Organometallics 2009, 28, 6234-6242. doi: 10.1021/om9006455 34. +LOO^^$^^)^^^/HH^^6^^%^^^3DUN^^-^^^6KDQJ^^5^^^:LOOLV^^$^^&^^^$QDORJLHV^EHWZHHQ^ Metallaboratranes, Triboronates, and Boron Pincer Ligand Complexes. Organometallics 2010, 29, 5661-5669. doi: 10.1021/om100557q 35. 2JDZD^^+^^^<DPDVKLWD^^0^^^7ULDO^IRU^DQWL-Markovnikov Hydration of 1-Decene Using Platinum Complexes Bearing a PBP Pincer Ligand, Inducing Alkene Isomerization and Decomposition of PBP Ligand. Chem. Lett. 2014, 43, 664-666. doi: 10.1246/cl.131208 36. 0F4XHHQ^^&^^0^^$^^^+LOO^^$^^)^^^6KDUPD^^0^^^6LQJK^^6^^.^^^:DUG^^-^^6^^^:LOOLV^^$^^&^^^ Young, R. D., Synthesis and reactivity of osmium and ruthenium PBP–LXL boryl pincer complexes. Polyhedron 2016, 120, 185-195. doi: 10.1016/j.poly.2016.05.041 37. 2JDZD^^+^^^<DPDVKLWD^^0^^^3ODWLQXP^FRPSOH[HV^EHDULQJ^D^ERURQ-based PBP pincer ligand: synthesis, structure, and application as a catalyst for hydrosilylation of 1-decene. Dalton Trans. 2013, 42, 625-629. doi: 10.1039/c2dt31892j 38. +DVHJDZD^^0^^^6HJDZD^^<^^^<DPDVKLWD^^0^^^1R]DNL^^.^^^,VRODWLRQ^RI^D^3%3-Pincer Rhodium Complex Stabilized by an Intermolecular C---+^ı Coordination as the Fourth Ligand. Angew. Chem. Int. Ed. 2012, 51, 6956-6960. doi: doi:10.1002/anie.201201916 39. )DQJ^^)^^^;XH^^0^^0^^^'LQJ^^0^^^=KDQJ^^-^^^/L^^6^^^&KHQ^^;^^^7KH^6WDELOLW\^RI^ 'LSKRVSKLQR^%RU\O^3%3^3LQFHU^%DFNERQH^^3%3^WR^323^/LJDQG^+\GURO\VLV^^Chemistry – An Asian Journal 2021, 16, 2489-2494. doi: 10.1002/asia.202100690 40. Lin, T.-3^^^3HWHUV^^-^^&^^^%RU\O-Mediated Reversible H
2 Activation at Cobalt: Catalytic Hydrogenation, Dehydrogenation, and Transfer Hydrogenation. J. Am. Chem. Soc. 2013, 135, 15310-15313. doi: 10.1021/ja408397v 41. 'LQJ^^<^^^0D^^4^-4^^^.DQJ^^-^^^=KDQJ^^-^^^/L^^6^^^&KHQ^^;^^^3DOODGLXP^,,^^FRPSOH[HV^ supported by PBP and POCOP pincer ligands: a comparison of their structure, properties and catalytic activity. Dalton Trans. 2019, 48, 17633-17643. doi: 10.1039/c9dt03954f 42. 7DQRXH^^.^^^<DPDVKLWD^^0^^^6\QWhesis of Pincer Iridium Complexes Bearing a Boron Atom and
iPr-Substituted Phosphorus Atoms: Application to Catalytic Transfer
Thomas Horstemeyer Docket No.: 222117-2220 Dehydrogenation of Alkanes. Organometallics 2015, 34, 4011-4017. doi: 10.1021/acs.organomet.5b00376 43. +LOO^^$^^)^^^0F4XHHQ^^&^^M. A., Arrested B–H Activation en Route to Installation of a PBP Pincer Ligand on Ruthenium and Osmium. Organometallics 2014, 33, 1977-1985. doi: 10.1021/om5001106 44. 0L\DGD^^7^^^<DPDVKLWD^^0^^^2[\JHQDWLRQ^RI^D^5XWKHQLXP^&RPSOH[^%HDULQJ^D^3%3- Pincer Ligand Inducing the Formation of a Boronato Ligand with a Weak Ru–O Bond. Organometallics 2013, 32, 5281-5284. doi: 10.1021/om400915x 45. +D\DVKL^^6^^^0XUD\DPD^^7^^^.XVXPRWR^^6^^^1R]DNL^^.^^^3LQFHU^6XSSRUWHG^ Perfluororhodacyclopentanes: High Nucleophilicity of WKH^0í&
F Bond. Angew. Chem. Int. Ed. 2022. doi: 10.1002/anie.202207760 46. Lin, T.-3^^^3HWHUV^^-^^&^^^%RU\O–Metal Bonds Facilitate Cobalt/Nickel-Catalyzed Olefin Hydrogenation. J. Am. Chem. Soc.2014, 136, 13672-13683. doi: 10.1021/ja504667f 47. 5tRV^^3^^^&XUDGR^^1^^^/ySH]-6HUUDQR^^-^^^5RGUtJXH]^^$^^^6HOHFWLYH^UHGXFWLRQ^RI^FDUERQ^ dioxide to bis(silyl)acetal catalyzed by a PBP-supported nickel complex. Chem. Commun. 2016, 52, 2114-2117. doi: 10.1039/C5CC09650B 48. 5tRV^^3^^^5RGUtJXH]^^$^^^/ySH]-6HUUDQR^^-^^^Mechanistic Studies on the Selective Reduction of CO2 to the Aldehyde Level by a Bis(phosphino)boryl (PBP)-Supported Nickel Complex. ACS Catal. 2016, 6, 5715-5723. doi: 10.1021/acscatal.6b01715 49. 'H]LHO^^$^^3^^^(VSLQRVD^^0^^5^^^3DYORYLF^^/^^^&KDUERQHDX^^'^^-^^^+D]DUL^^1^^^+RSPDQQ^^ .^^+^^^0HUFDGR^^%^^4^^^/LJDQG^DQG^VROYHQW^HIIHFWV^RQ^&2
2 insertion into group 10 metal alkyl bonds. Chem. Sci. 2022, 13, 2391-^^^^^^GRL^^^^^^^^^^G^VF^^^^^G^^&RPSOH[^1 has been prepared by us following a different procedure which will be published as part of an forthcoming paper. 50. &XUDGR^^1^^^0D\D^^&^^^/ySH]-6HUUDQR^^-^^^5RGUtJXH]^^$^^^%RU\O-assisted hydrogenolysis of a nickel–methyl bond. Chem. Commun. 2014, 50, 15718-15721. doi: 10.1039/C4CC07616H 51. 6HLGHO^^)^^:^^^1R]DNL^^.^^^$^1L^^ı-Borane Complex Bearing a Rigid Bidentate Borane/Phosphine Ligand: Boryl Complex Formation by Oxidative Dehydrochloroborylation and Catalytic Activity for Ethylene Polymerization. Angew. Chem. Int. Ed. 2022, 61, e202111691. doi: 10.1002/anie.202111691
Thomas Horstemeyer Docket No.: 222117-2220 52. Fontaine, F.-*^^^=DUJDULDQ^^'^^^0H
2AlCH
2PMe
2: A New, Bifunctional Cocatalyst for the Ni(II)-Catalyzed Oligomerization of PhSiH
3. J. Am. Chem. Soc. 2004, 126, 8786-8794. doi: 10.1021/ja048911m 53. &KDQGUDQ^^'^^^%\HRQ^^6^^-^^^6XK^^+^^^.LP^^,^^^(IIHFW^RI^,RQ-Pair Strength on Ethylene Oligomerization by Divalent Nickel Complexes. Catal. Lett. 2013, 143, 717-722. doi: 10.1007/s10562-013-1021-7 54. 'UHVFK^^/^^&^^^GH^$UD~MR^^%^^%^^^&DVDJUDQGH^ 2^^G^^/^^^6WLHOHU^^5^^^$^QRYHO^FODVV^RI^ nickel(ii) complexes containing selenium-based bidentate ligands applied in ethylene oligomerization. RSC Advances 2016, 6, 104338-104344. doi: 10.1039/C6RA18987C 55. +XDQJ^^<^^^=KDQJ^^/^^^:HL^^:^^^$ODP^^)^^^-LDQJ^^T., Nickel-based ethylene oligomerization catalysts supported by PNSiP ligands. Phosphorus, Sulfur Silicon Relat. Elem. 2018, 193, 363-368. doi: 10.1080/10426507.2018.1424157 56. ;X^^&^^^6KHQ^^4^^^6XQ^^;^^^7DQJ^^<^^^6\QWKHVLV^^&KDUDFWHUL]DWLRQ^^DQG^+LJKO\^Selective Ethylene Dimerization to 1-%XWHQH^RI^>2í1;@1L^,,^^&RPSOH[HV^^Chin. J. Chem . 2012, 30, 1105-1113. doi: 10.1002/cjoc.201100443 57. Ziegler, K., Aluminium-organische Synthese im Bereich olefinischer Kohlenwasserstoffe. Angew. Chem. 1952, 64, 323-329. doi: 10.1002/ange.19520641202 58. +RODK^^'^^*^^^+XJKHV^^$^^1^^^+XL^^%^^&^^^.DQ^^&^-T., Production of Ni(I) complexes from reactions between Ni(II) and NaBH
4 in the presence of triphenylphosphine and some bidentate phosphines. Can. J. Chem. 1978, 56, 2552-2559. doi: 10.1139/v78-419 59. &KDQGUDQ^^'^^^/HH^^.^^0^^^&KDQJ^^+^^&^^^6RQJ^^*^^<^^^/HH^^-^-(^^^6XK^^+^^^.LP^^,^^^ Ni(II) complexes with ligands derived from phenylpyridine, active for selective dimerization and trimerization of ethylene. J. Organomet. Chem. 2012, 718, 8-13. doi: 10.1016/j.jorganchem.2012.08.005 60. =KDQJ^^0^^^=KDQJ^^6^^^+DR^^3^^^-LH^^6^^^6XQ^^:^-+^^^/L^^3^^^/X^^;^^^1LFNHO^&RPSOH[HV^ Bearing 2-(Benzimidazol-2-yl)-1,10-phenanthrolines: Synthesis, Characterization and Their Catalytic Behavior Toward Ethylene Oligomerization. Eur. J. Inorg. Chem. 2007, 2007, 3816-3826. doi: 10.1002/ejic.200700392 61. $QWRQRY^^$^^$^^^6HPLNROHQRYD^^1^^9^^^6RVKQLNRY^^,^^(^^^7DOVL^^(^^3^^^%U\OLDNRY^^.^^3^^^ Selective Ethylene Dimerization into 2-Butenes Using Homogeneous and Supported Nickel(II) 2-Iminopyridine Catalysts. Top. Catal. 2020, 63, 222-228. doi: 10.1007/s11244- 019-01208-8
Thomas Horstemeyer Docket No.: 222117-2220 62. %RXGLHU^^$^^^%UHXLO^^3^-$^^5^^^0DJQD^^/^^^2OLYLHU-%RXUELJRX^^+^^^%UDXQVWHLQ^^3^^^ Nickel(II) complexes with imino-imidazole chelating ligands bearing pendant donor groups (SR, OR, NR
2, PR
2) as precatalysts in ethylene oligomerization. J. Organomet. Chem. 2012, 718, 31-37. doi: 10.1016/j.jorganchem.2012.07.044 63. )HQJ^^&^^^=KRX^^6^^^:DQJ^^'^^^=KDR^^<^^^/LX^^6^^^/L^^=^^^%UDXQVWHLQ^^3^^^&RRSHUDWLYLW\^ in Highly Active Ethylene Dimerization by Dinuclear Nickel Complexes Bearing a Bifunctional PN Ligand. Organometallics 2021, 40, 184-193. doi: 10.1021/acs.organomet.0c00683 64. +DJKYHUGL^^0^^^7DGMDURGL^^$^^^%DKUL^/DOHK^^1^^^1HNRRPDQHVK^+DJKLJKL^^0^^^ 6\QWKHVLV^DQG^FKDUDFWHUL]DWLRQ^RI^1L^,,^^FRPSOH[HV^EHDULQJ^RI^^^^^H–EHQ]LPLGD]RO^^^\O^^ phenol derivatives as highly active catalysts for ethylene oligomerization. Appl. Organomet. Chem. 2018, 32. doi: 10.1002/aoc.4015 65. 0XNKHUMHH^^6^^^3DWHO^^%^^$^^^%KDGXUL^^6^^^6HOHFWLYH^(WK\OHQH^2OLJRPHUL]DWLRQ^ZLWK^ Nickel Oxime Complexes. Organometallics 2009, 28, 3074-3078. doi: 10.1021/om900080h 66. *XWVXO\DN^^'^^9^^^*RWW^^$^^/^^^3LHUV^^:^^(^^^3DUYH]^^0^^^'LPHUL]DWLRQ^RI^(WK\OHQH^E\^ Nickel Phosphino–Borate Complexes. Organometallics 2013, 32, 3363-3370. doi: 10.1021/om400288u 67. %RXOHQV^^3^^^3HOOLHU^^(^^^-HDQQHDX^^(^^^5HHN^^-^^1^^+^^^2OLYLHU-%RXUELJRX^^+^^^%UHXLO^^ P.-A. R., Self-Assembled Organometallic Nickel Complexes as Catalysts for Selective Dimerization of Ethylene into 1-Butene. Organometallics 2015, 34, 1139-1142. doi: 10.1021/acs.organomet.5b00055 68. The transition state observed for S=0 (singlet state) is 49.0 kcal mol
í1. Nonetheless, the diradical species (S=1) was also considered, as described in reference 21. However, this barrier was even higher in Gibbs free energy (83.4 kcal mol
í1). 69. 5tRV^^3^^^%RUJH^^-^^^)HUQiQGH]^'H^&yUGRYD^^)^^^6FLRUWLQR^^*^^^/OHGyV^^$^^^5RGUtJXH]^^ A., Ambiphilic boryl groups in a neutral Ni(II) complex: a new activation mode of H
2. Chem. Sci. 2021, 12, 2540-2548. doi: 10.1039/d0sc06014c 70. +H^^7^^^7VYHWNRY^^1^^3^^^$QGLQR^^-^^*^^^*DR^^;^^^)XOOPHU^^%^^&^^^&DXOWRQ^^.^^*^^^ Mechanism of Heterolysis of H
2 by an Unsaturated d
8 Nickel Center: via Tetravalent Nickel? J. Am. Chem. Soc. 2010, 132, 910-911. doi: 10.1021/ja908674x 71. &UDLJ^^1^^&^^^*URQHU^^3^^^0F.HDQ^^'^^&^^^(TXLOLEULXP^6WUXFWXUHV^IRU^%XWDGLHQH^DQG^ (WK\OHQH^ௗ^&RPSHOOLQJ^(YLGHQFH^IRU^Ȇ-Electron Delocalization in Butadiene. J. Phys. Chem. A. 2006, 110, 7461-7469. doi: 10.1021/jp060695b
Thomas Horstemeyer Docket No.: 222117-2220 72. %URRNKDUW^^0^^^*UHHQ^^0^^/^^+^^^3DUNLQ^^*^^^$JRVWLF^LQWHUDFWLRQV^LQ^WUDQVLWLRQ^PHWDO^ compounds. Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 6908-6914. doi: 10.1073/pnas.0610747104 73. )XOPHU^^*^^5^^^0LOOHU^^$^^-^^0^^^6KHUGHQ^^1^^+^^^*RWWOLHE^^+^^(^^^1XGHOPDQ^^$^^^6WROW]^^ %^^0^^^%HUFDZ^^-^^(^^^*ROGEHUJ^^.^^,^^^105^&KHPLFDO^6KLIWV^RI^7UDFH^,PSXULWLHV^^&RPPRQ^ Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist. Organometallics 2010, 29, 2176-2179. doi: 10.1021/om100106e It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. In an embodiment, the term “about” can include traditional rounding according to significant figures of the numerical value. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”. It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations, and are set forth only for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure.
, wherein Q is B, Al, Ga, In, or Tl, wherein each R is independently selected from an alkyl or aryl group, where X is a halogen, acetoxy group (OAc), or polyatomic ion (e.g., BF4-, PF6-, BAr4- (Ar = aryl group) etc.).
Thomas Horstemeyer Docket No.: 222117-2220 In an embodiment, the present disclosure provides for a method of making linear alpha olefins (LAO)s and internal olefins, comprising reacting ethylene with the composition described above or compositions described herein. BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present disclosure will be more readily appreciated upon review of the detailed description of its various embodiments, described below, when taken in conjunction with the accompanying drawings. Figure 1 illustrates isomerization of 1-butene. Reaction conditions: (RPBP)NiBr ^^^^^^^^PRO^^^(W$O&O2 ^^^^^^^PRO^^^XVLQJ^WROXHQH^DV^WKH^VROYHQW^^^^P/^WRWDO^IRU^HDFK^ UHDFWLRQ^^^^^^SVLJ^^-butene at room temperature for 120 min. Figure 2 illustrates an excerpt of the Gibbs energy profile for the reaction of two equivalents of ethylene and [(tBuPBP)Ni]+ (5) to form a product 6 with two ethylene ligands and a dissociated phosphine. Relative Gibbs energies at 298 K and 1 M in kcal molí^. Hydrogen atoms on the (RPBP)Ni moiety have been omitted for clarity. Figure 1 illustrates frontier molecular orbitals involved in TS1, which provides C–C formation between two equivalents of ethylene. Figure 2 illustrates an excerpt of the Gibbs energy profile for Ni-mediated C–C coupling of two ethylene ligands (TS2) to ultimately form complex 8, which possesses a Ni/CH2 agnostic interaction. Relative Gibbs energies at 298 K and 1 M in kcal molí^. Hydrogen atoms on the (RPBP)Ni system have been omitted for clarity. Figure 3 illustrates an excerpt of the Gibbs energy profile for the reaction of ethylene DQG^^^^ȕ-hydride eliminations and hydride transfer). Relative Gibbs energies at 298 K and 1 M in kcal molí^. Hydrogen atoms on the (RPBP)Ni system have been omitted for clarity. Figure 4 illustrates an excerpt of the Gibbs energy profile for the reaction of ethylene and 5 (hydride orbiting and formation of 1-butene). Relative Gibbs energies at 298 K and 1 M in kcal molí^. Hydrogen atoms on the (RPBP)Ni system have been omitted for clarity. Figure 7, Scheme 1 illustrates previously proposed mechanisms for Ni-mediated ethylene oligomerization. Figure 8, Scheme 2 illustrates examples of previously reported reactions of olefins with PBP-Ni and related PB-Ni complexes and this work.
Thomas Horstemeyer Docket No.: 222117-2220 Figure 9(A) illustrates control experiments using other Ni pre-catalysts without the RPBP ligand, which establishes the importance of the RPBP ligand to successful catalysis. Figure 9(B) illustrates attempts for propylene dimerization using (RPBP)Ni complexes 1–3. Figure 10 illustrates selectivity of ethylene oligomerization using (tBuPBP)NiBr (2), (PhPBP)NiBr (3) and (CyPBP)NiBr (4). Figure 11 illustrates halide abstraction from complex 2 to give cationic complex 5. Figure 12 illustrates observed products using (tBuPBP)NiBr with MAO under ethylene, propylene, or a mixture of propylene with ethylene. DETAILED DESCRIPTION In general, the present disclosure provides for catalytic precursors, methods of making catalytic precursors, and method of catalytic alkene oligomerization reactions. Additional details are provided below, in Example 1 and in the claims. Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims. Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit (unless the context clearly dictates otherwise), between the upper and lower limit of that range, and any other stated or intervening value in that stated range, is encompassed within the disclosure. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described. As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other
Thomas Horstemeyer Docket No.: 222117-2220 several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible. Embodiments of the present disclosure will employ, unless otherwise indicated, techniques of chemistry, inorganic chemistry, synthetic chemistry, and the like, which are within the skill of the art. Such techniques are explained fully in the literature. The following description and examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to perform the methods and use the compositions and compounds disclosed and claimed herein. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C, and pressure is in bar or psig. Standard temperature and pressure are defined as 25 °C and 1 bar. Before the embodiments of the present disclosure are described in detail, it is to be understood that, unless otherwise indicated, the present disclosure is not limited to particular materials, reagents, reaction materials, manufacturing processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It is also possible in the present disclosure that steps can be executed in different sequence where this is logically possible. Different stereochemistry is also possible, such as products of cis or trans orientation around a carbon–carbon double bond or syn or anti addition could be both possible even if only one is drawn in an embodiment. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a support” includes a plurality of supports. In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings unless a contrary intention is apparent. Definitions: By “chemically feasible” is meant a bonding arrangement or a compound where the generally understood rules of organic structure are not violated. The structures disclosed herein, in all of their embodiments are intended to include only “chemically feasible” structures, and any recited structures that are not chemically feasible, for example in a
Thomas Horstemeyer Docket No.: 222117-2220 structure shown with variable atoms or groups, are not intended to be disclosed or claimed herein. However, if a bond appears to be intended and needs the removal of a group such as a hydrogen from a carbon, the one of skill would understand that a hydrogen could be removed to form the desired bond. The term "substituted” refers to any one or more hydrogen atoms on the designated atom (e.g., a carbon atom) that can be replaced with a selection from the indicated group (e.g., halide, hydroxyl, alkyl, and the like), provided that the designated atom’s normal valence is not exceeded. As used herein, the term “optionally substituted” typically refers to from zero to four substituents, wherein the substituents are each independently selected. Each of the independently selected substituents may be the same or different than other substituents. For example, the substituents (e.g., an R type group) of a formula may be optionally substituted (e.g., from 1 to 4 times) with independently selected H, halogen, hydroxy, acyl, alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclo, aryl, heteroaryl, alkoxy, amino, amide, thiol, sulfone, sulfoxide, oxo, oxy, nitro, carbonyl, carboxy, amino acid sidechain, amino acid, etc. In an embodiment, substituted includes substitution with a halogen. As used herein, a “derivative” of a compound refers to a chemical compound that may be produced from another compound of similar structure in one or more steps, as in replacement of H by an alkyl, acyl, amino group, etc. As used herein, “aliphatic” or “aliphatic group” refers to a saturated or unsaturated, linear or branched, cyclic (non-aromatic) or heterocyclic (non-aromatic), hydrocarbon or hydrocarbon group, where each can be substituted or unsubstituted, and encompasses alkyl, alkenyl, and alkynyl groups, and alkanes, alkene, and alkynes, for example, substituted or unsubstituted. As used herein, “alkane” refers to a saturated aliphatic hydrocarbon which can be straight or branched, having 1 to 40, 1 to 20, 1 to 10, or 1 to 5 carbon atoms, where the stated range of carbon atoms includes each intervening integer individually, as well as sub-ranges. Examples of alkane include, but are not limited to methane, ethane, propane, butane, pentane, and the like. Reference to “alkane” includes unsubstituted and substituted forms of the hydrocarbon moiety. As used herein, “alkyl” or “alkyl group” refers to a saturated aliphatic hydrocarbon, which can be straight or branched, having 1 to 40, 1 to 20, 1 to 10, or 1 to 5 carbon atoms, where the stated range of carbon atoms includes each intervening integer individually, as well
Thomas Horstemeyer Docket No.: 222117-2220 as sub-ranges. Examples of alkyl groups include, but are not limited to methyl, ethyl, n- propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, and s-pentyl. Reference to “alkyl” or “alkyl group” includes unsubstituted and substituted forms of the hydrocarbon moiety. As used herein, “alkene” (also referred to as an “olefin”) refers to an aliphatic hydrocarbon which can be straight or branched, containing at least one carbon-carbon double bond, having 2 to 40, 2 to 20, 2 to 10, or 2 to 5 carbon atoms and can also be have 4 to 30 carbons, 4 to 21 carbons, or 6 to 20 carbons, where the stated range of carbon atoms includes each intervening integer individually, as well as sub-ranges. Examples of alkene groups include, but are not limited to, ethylene, propylene, butene, 1-pentene, 1-hexene, isobutene and the like. Reference to “alkene” includes unsubstituted and substituted forms of the hydrocarbon moiety. As used herein, “alkyl” or “alkyl group” refers to a saturated aliphatic hydrocarbon, which can be straight or branched, having 1 to 40, 1 to 20, 1 to 10, or 1 to 5 carbon atoms, where the stated range of carbon atoms includes each intervening integer individually, as well as sub-ranges. Examples of alkyl groups include, but are not limited to methyl, ethyl, n- propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, and s-pentyl. Reference to “alkyl” or “alkyl group” includes unsubstituted and substituted forms of the hydrocarbon moiety. “Aryl”, as used herein, refers to C5-C20-membered aromatic, heterocyclic, fused aromatic, fused heterocyclic, biaromatic, or bihetereocyclic ring systems. In an aspect, “aryl”, can include 5-, 6-, 7-, 8-, 9-, and 10-membered single-ring aromatic groups that may include from zero to four heteroatoms, for example, functional groups that correspond to benzene, pyrrole, furan, thiophene, imidazole, oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazine and pyrimidine, and the like. Those aryl groups having heteroatoms in the ring structure may also be referred to as “aryl heterocycles” or “heteroaromatics”. The aromatic ring can be substituted at one or more ring positions with one or more substituents including, but not limited to, halogen, azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino (or quaternized amino), nitro, sulfhydryl, imino, amido, phosphonate, phosphinate, carbonyl, carboxyl, silyl, ether, alkylthio, sulfonyl, sulfonamido, ketone, aldehyde, ester, heterocyclyl, aromatic or heteroaromatic moieties, -CF3, -&1^^DQG^ combinations thereof. The term “aryl” also includes polycyclic ring systems (C5-C30) having two or more cyclic rings in which two or more carbons are common to two adjoining rings (i.e., “fused rings”) wherein at least one of the rings is aromatic, e.g., the other cyclic ring or rings can be
Thomas Horstemeyer Docket No.: 222117-2220 cycloalkyls, cycloalkenyls, cycloalkynyls, aryls and/or heterocycles. Examples of heterocyclic rings include, but are not limited to, benzimidazolyl, benzofuranyl, benzothiofuranyl, benzothiophenyl, benzoxazolyl, benzoxazolinyl, benzthiazolyl, benztriazolyl, benztetrazolyl, benzisoxazolyl, benzisothiazolyl, benzimidazolinyl, carbazolyl, 4aH carbazolyl, carbolinyl, chromanyl, chromenyl, cinnolinyl, decahydroquinolinyl, 2H,6H- 1,5,2-dithiazinyl, dihydrofuro[2,3 b]tetrahydrofuran, furanyl, furazanyl, imidazolidinyl, imidazolinyl, imidazolyl, 1H-indazolyl, indolenyl, indolinyl, indolizinyl, indolyl, 3H-indolyl, isatinoyl, isobenzofuranyl, isochromanyl, isoindazolyl, isoindolinyl, isoindolyl, isoquinolinyl, isothiazolyl, isoxazolyl, methylenedioxyphenyl, morpholinyl, naphthyridinyl, octahydroisoquinolinyl, oxadiazolyl, 1,2,3-oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, oxazolidinyl, oxazolyl, oxindolyl, pyrimidinyl, phenanthridinyl, phenanthrolinyl, phenazinyl, phenothiazinyl, phenoxathinyl, phenoxazinyl, phthalazinyl, piperazinyl, piperidinyl, piperidonyl, 4-piperidonyl, piperonyl, pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolidinyl, pyrazolinyl, pyrazolyl, pyridazinyl, pyridooxazole, pyridoimidazole, pyridothiazole, pyridinyl, pyridyl, pyrimidinyl, pyrrolidinyl, pyrrolinyl, 2H-pyrrolyl, pyrrolyl, quinazolinyl, quinolinyl, 4H-quinolizinyl, quinoxalinyl, quinuclidinyl, tetrahydrofuranyl, tetrahydroisoquinolinyl, tetrahydroquinolinyl, tetrazolyl, 6H-1,2,5-thiadiazinyl, 1,2,3- thiadiazolyl, 1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl, 1,3,4-thiadiazolyl, thianthrenyl, thiazolyl, thienyl, thienothiazolyl, thienooxazolyl, thienoimidazolyl, thiophenyl and xanthenyl. One or more of the rings can be substituted as defined above for “aryl”. As used herein, “halo”, “halogen”, “halide”, or “halogen radical” refers to a fluorine, chlorine, bromine, iodine, and astatine, and radicals thereof. Further, when used in compound words, such as “haloalkyl” or “haloalkenyl”, “halo” refers to an alkyl or alkenyl radical in which one or more hydrogens are substituted by halogen radicals. Examples of haloalkyl include, but are not limited to, trifluoromethyl, trichloromethyl, pentafluoroethyl, and pentachloroethyl. As used herein, “cyclic” hydrocarbon refers to any stable 4, 5, 6, 7, 8, 9, 10, 11, or 12 membered, (unless the number of members is otherwise recited), monocyclic, bicyclic, or tricyclic cyclic ring. As used herein, “olefin” is a hydrocarbon that includes at least one double bond. An alpha olefin ^Į-olefin) has a double bond at the alpha or primary position, whereas an internal olefin includes a double bond within the hydrocarbon chain that is not in the alpha position.
Thomas Horstemeyer Docket No.: 222117-2220 As used herein, the term “purified” and like terms relate to an enrichment of a molecule or compound relative to other components normally associated with the molecule or compound in a native environment. The term “purified” does not necessarily indicate that complete purity of the particular molecule has been achieved during the process. A “highly purified” compound as used herein refers to a compound that is greater than 90% pure. General Discussion The present disclosure provides for catalytic precursors, methods of making catalytic precursors, method of catalytic alkene oligomerization reactions, methods of converting ethylene to linear alpha olefins or internal olefins. In some aspects the present disclosure provides for (RPQP)NiBr (Q = B, Al, Ga, In, or Tl, R = an alkyl or aryl group, for example t%X^^3K^^RU^&\^^;^ ^KDORJHQ^^H^g., Br), OAc, or polyatomic ion) catalyst precursors and catalytic ethylene oligomerization reaction methods. Example 1 provides illustrations of the versatility of the present disclosure. In one aspect, the present disclosure provides for methods that illustrate ethylene dimerization is generally selective for the formation of terminal 1-butene, and that the features of catalysis are dependent on ligand identity. The reactions proceed by using (tBuPBP)NiOAc (1) without co-catalyst, as well as mixing (RPBP)NiBr with Ag+ or Na+ salts, alkylaluminum, or other Lewis acids (e.g., BF3, BBr3, and AlCl3). The (PhPBP)Ni complex shows significant activity for the production of butenes with a TOF up to 274(34) molbutenes·molNi í^·sí^ (41(1)% selective for 1-butene), while the (tBuPBP)Ni complex shows good selectivity for 1-butene with a TOF up to 33(2) molbutenes·molNi í^·sí^ (87(0)% selective for 1-butene). The PBP-Ni activation of ethylene and proposed mechanism is unique for the conversion of ethylene to higher olefins. Additional details are provided in Example 1. In an aspect, the present disclosure provides for Ni catalysts that convert ethylene to linear alpha olefins with high reaction rates and selectivity. A characteristic of these catalysts is the presence of a Lewis acidic moiety bonded to the Ni center. In an aspect, the present disclosure provides for (RPQP)NiX, where Q is B, Al, Ga, In, or Tl, where each R can be independently selected from an alkyl or aryl group such as a t- butyl group (tBu), phenyl group (Ph), or a cyclohexyl group (Cy), where X is a halogen like Br or X is acetoxy group (OAc) or a polyatomic ion such as BF4-, PF6-, BAr4- (Ar = aryl
Thomas Horstemeyer Docket No.: 222117-2220 group), etc. The (RPQP)NiX compound can have the following structure:
. In a particular aspect, the present disclosure provides for (RPBP)NiX, where each R can be independently selected from an alkyl or aryl group such as a t-butyl group (tBu), phenyl group (Ph), or a cyclohexyl group (Cy), where X is a halogen like Br or X is acetoxy group (OAc) or a polyatomic ion such as BF4- or PF6-. In an aspect, each R can be the same. The (RPBP)NiX compound can have the following structure:
, where X is a halogen like Br or X is acetoxy group (OAc) or a polyatomic ion such as BF4- or PF6-. The present disclosure provides for the catalytic transformation to convert ethylene and/or D-olefins (e.g., C3 to C20), to higher olefins (C5 to C21 or C6 to C20 oligomers). For example, Figure 12 illustrates the observed products using (tBuPBP)NiBr with MAO under ethylene, propylene, or a mixture of propylene with ethylene. In particular, the present disclosure provides for selective coupling of ethylene and 1-hexene to give 1-octene. Each of the reactions can optionally be conducted in a single container (e.g., “one pot synthesis”). In an embodiment, each of the reactions can be conducted at about room temperature. The reaction time for each can be about 5 mins to 5 days, about 12 to 36 hours, or about 24 hours. In an embodiment the amount of (RPQP)NiX can be about 0.1 to 10 μmol. In an embodiment, the amounts of other components such as Ag+ or Na+ salts, alkylaluminum, or other Lewis acids (e.g., BF3, BBr3, and AlCl3) can each independently be about 1 to 1000 equivalents, about 2 to 20 equivalents, or about 2 to 15 equivalents relative to catalyst. Additional details are provided in Example 1. Ethylene (and/or the D-olefin) pressure can vary from ambient (e.g., about 15 psi) up to high pressures (e.g., up to 2000 psi or greater). In an embodiment, the products (e.g., butenes (e.g., 1-butene)) can be produced with about 50, 60, 70, 80, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99, each up to 100% selectivity (e.g., about 50 to 100%). In one aspect the yield is about 50, 60, 70, 80, or 90, each up to 100% (e.g., about 50 to 100%, about 70 to 100%, or about 80 to 100%). In an embodiment,
Thomas Horstemeyer Docket No.: 222117-2220 the product can be produced with high selectivity (e.g., about 70% to 100%), for example for 1-butene. In addition to the (RPQP)NiX, the following materials can be included in the reaction: solvent (e.g., toluene, etc.), air (e.g., at ambient to 5000 psi), and N2 (e.g., at ambient to 5000 psi). In regard to each of the reactions described herein, each can optionally be conducted in a single container and at about room temperature. The reaction time for each can be about 5 mins to 5 days, about 12 to 36 hours, or about 24 hours. In an embodiment the amount of compound used (e.g., (RPQP)NiX) can be about 0.1 to 10 μmol. In an embodiment, the amounts of other components such as Ag+ or Na+ salts, alkylaluminum, or other Lewis acids (e.g., BF3, BBr3, and AlCl3) can each independently be about 1 to 1000 equivalents, about 2 to 20 equivalents, or about 2 to 15 equivalents relative to catalyst. Ethylene (and/or the D- olefin) pressure can vary from ambient up to high pressures. EXAMPLES Now having described the embodiments of the disclosure, in general, the examples describe some additional embodiments. While embodiments of the present disclosure are described in connection with the example and the corresponding text and figures, there is no intent to limit embodiments of the disclosure to these descriptions. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of embodiments of the present disclosure. Example 1: Introduction Catalytic oligomerization of ethylene is an important commercial method for the proGXFWLRQ^RI^OLQHDU^Į-olefins (LAOs), which have extensive uses in fuel, petro-, and fine chemistry.1-4 Each year, > 3.5 million tons of LAOs are produced globally, and the annual growth rate of world consumption of LAOs forecasted to be approximately 4% during the 2019–2024 period.5,6 Since the first discovery of the "nickel effect" by Ziegler and Holzkamp in the 1950s,7 the field of nickel catalyzed olefin oligomerization has become one of intense study. Thus, the development of new catalysts for Ni-catalyzed olefin oligomerization and studies of the reaction mechanisms continue to be of interest to academia and industry.8-10 Another important milestone in this field was the development of the bidentate P–O ligated
Thomas Horstemeyer Docket No.: 222117-2220 Ni complex by Keim and coworkers,11 which ultimately led to the commercialization of the Shell higher olefin process (SHOP) that is used for the production of over one million tons of Į-olefins every year.2,12-13 This success has encouraged recent studies with the goal of pursuing novel ligand structures to develop new fundamental understanding of how ligand/catalyst structure can impart new types of reactivity.12 The generally accepted mechanism for Ni-mediated ethylene oligomerization (e.g., the SHOP process) is the Cossee-Arlman mechanism (Figure 7, left)5,9,14-15 in which the reaction is initiated from a Ni–H/alkyl intermediate followed by ethylene insertion steps ^FKDLQ^JURZWK^^^7KH^IRUPDWLRQ^RI^ROHILQ^SURGXFWV^LV^JHQHUDOO\^SURSRVHG^WR^RFFXU^YLD^ȕ-H elimination from a Ni-alkyl intermediate followed by net olefin dissociation. Chain propagaWLRQ^LV^QRUPDOO\^FRQWUROOHG^E\^WKH^UDWLR^RI^HWK\OHQH^LQVHUWLRQ^DQG^ȕ-H elimination rates,10 DQG^IUHTXHQWO\^6FKXO]í)ORU\^GLVWULEXWLRQV^RI^HWK\OHQH^ROLJRPHUV^DUH^REWDLQHG^16-18 Another possible mechanism for Ni-catalyzed ethylene oligomerization involves the formation of a metallacycle similar to the reactions using Cr catalysts,9,19 which is normally proposed in the reaction of a Ni pre-catalyst with a Lewis acid activator (e.g., BF3).20 This type of mechanism has been suggested to be energetically viable based on DFT modeling of phosphine ligated Ni(0) catalyzed ethylene dimerization processes (Figure 7, right).2,21 Experimental evidence for a Ni metallacycle mechanism (Figure 7, right) was reported by Grubbs and coworkers using a nickel-based metallacyclopentene complex in the 1970s.22-26 Pincer ligands have been widely used in transition-metal-mediated catalysis due, in part, to their tunable steric and electronic properties.27-30 As part of the pincer ligand family, examples of bis(phosphino)boryl ligands (RPBP) have been designed and synthesized by the Nozaki and Yamashita groups,31-33 and later, (RPBP) ligands were studied with transition- metals such as Os, Ir, Pt, Ru, Rh, Pd and Co.34-45 Nickel complexes with tBuPBP ligands have been isolated and reported to be active for olefin hydrogenation and CO2 reduction.46-49 In DGGLWLRQ^^H[SHULPHQWDO^HYLGHQFH^KDV^EHHQ^UHSRUWHG^IRU^WKH^IRUPDWLRQ^RI^D^ı-ERUDQH^^^2-B– H)Ni(0) species from the reaction of (tBuPBP)NiH with 1,5-cyclooctadiene, which suggests that the hydride ligand is capable of migration from the Ni center to the boron center (Figure 8).505HFHQWO\^^WKH^1R]DNL^JURXS^KDV^V\QWKHVL]HG^D^ELGHQWDWH^1L^^^^ı-borane complex {(^2-B– H/P)Ni} and demonstrated its application in catalytic polymerization of ethylene for which the (^2-B–H/P)Ni complex behaves as a masked Ni(II) boryl hydride that selectively produces linear polyethylene but not lower molecular weight ethylene oligomers (Figure 8).51 These studies suggest that the installation of a non-innocent boryl-moiety in the ligand
Thomas Horstemeyer Docket No.: 222117-2220 structure offers unique reactivity, such as serving as a hydride shuttle, and could potentially alter the reaction pathway for catalytic processes. This example describes catalytic ethylene oligomerization reactions using a series of (RPBP)NiBr (R = tBu, Ph, or Cy) catalyst precursors. Unique aspects of these catalytic processes include substantial activities for ethylene dimerization with an Al-based or Lewis acid co-catalysts, tunable selectivity for ethylene dimerization versus oligomerization based on ligand structure and co-catalyst identity, and a proposed catalytic reaction pathway that involves a non-innocent boron center on the ligand moiety and does not involve a Ni–H or Ni–alkyl intermediate, which we believe is a unique mechanism for olefin coupling processes. Results and Discussion Initial screening for ethylene dimerization. During the initial screening via in situ 1H NMR spectroscopy, (tBuPBP)NiOAc (1), which was synthesized from (tBuPBP)NiMe and CO2,49 was found to catalyze slow dimerization of ethylene to form 1-butene without a co- catalyst at 90 °C using C6D6 as the solvent (Table 1, entry 1). To test if the acetate group is required for the reaction, (tBuPBP)NiBr (2) was used, and no peaks associated with the formation of butenes were observed in the
spectra (Table 1, entry 2). However, when using complex 2 in the presence of AgBF4 as an additive for bromide abstraction, the ethylene dimerization reaction was achieved even at a lower temperature (60 °C) with ~75% selectivity for 1-butene (Table 1, entry 3). In an effort to achieve an in situ Br/OAc metathesis reaction to form complex 1, both TlOAc and AgOAc were examined as the additive for the ethylene dimerization reaction using complex 2 (Table 1, entry 4). The reaction with TlOAc after 2 days provided < 1 TO (turnover) of 1-butene (Table 1, entry 5). Based on these results, it can be concluded that the OAc group is likely not essential for the ethylene dimerization, and we speculated that cationic [(tBuPBP)Ni]BF4, formed through bromide abstraction from 2 with AgBF4, is likely the active species for the ethylene dimerization reaction. Although we were unable to isolate the cationic complex [(tBuPBP)Ni][BF4], a crystal structure of [(tBuPBP)Ni(OH2)][BF4] was obtained, which likely formed during the month-long crystal growing period in an insufficiently dried solvent. Next, different silver and sodium salts were tested as additives (see Supporting Information, Section 2), and only AgBF4, AgSbF6, AgBArF and NaBArF were found to provide active catalysts for ethylene dimerization in the presence of complex 2 (Table 1,
Thomas Horstemeyer Docket No.: 222117-2220 entries 3, 6–8). Control experiments using other Ni precursors such as (DME)NiCl2, NiCl2 and Ni(OAc)2 with and without AgBF4 showed no activity for ethylene dimerization (Figure 9A), which suggests that the tBuPBP ligand is important for the dimerization reaction, leading us to speculate about a possible cooperative role for the Ni and B centers in the catalytic mechanism (see below for more discussion on this point). The Ni(II) complex (PhPBP)NiBr (3) was synthesized and tested for ethylene dimerization, and we found that using 3 as a catalyst precursor yielded butenes at room temperature, but the reaction was less selective for 1-butene (Table 1, entries 9–11). It is possible that changing the tBu group to a less sterically hindered Ph group on the PBP moiety favors the coordination of 1-butene, which might provide access to a more facile isomerization of 1-butene to 2-butenes compared to the Ni catalyst coordinated by the tBuPBP ligand (see below for more discussion and experimental results supporting this suggestion). Propylene was also tested as the substrate using complexes 1–3 in the presence of additives (i.e., AgBF4^^0$2^^^KRZHYHU^^QR^UHDFWLRQ^ZDV^REVHUYHG^EDVHG^RQ^WKH^in situ
NMR studies (Figure 9B). However, a mixture of propylene and ethylene resulted in the formation of higher olefins with an odd number of carbon atoms along with products from ethylene oligomerization. These results indicate the likelihood of a Ni-catalyzed coupling reaction between ethylene and propylene, which also indicates that the coupling of ethylene and other D-olefins, such as 1-butene, is possible. Thus, the Ni-catalysis is selective toward homo- ethylene coupling or ethylene/D-olefin coupling but is less reactive for the coupling of two D- olefins. Table 1. Initial attempts for ethylene dimerization using (RPBP)Ni complexes.a
Ni Time Temp. TOF C4 b 1-butene 2-butenes (TOs) Entry Additive complex (min) (°C) (sí^) (TOs) trans cis 1 1 none 1440 90 3×10í^ 2.3 N.D. N.D. 2 2 none 240 60 N.D.c N.D. N.D. N.D. 3 2 AgBF4 240 60 1×10í^ 1.1 0.24 0.12
Thomas Horstemeyer Docket No.: 222117-2220 2 AgOAc 1440 60 N.D. N.D. N.D. N.D. 2 TlOAc 2880 60 6×10í^ 0.8 N.D. N.D. 2 NaBArF 240 60 9×10í^ 0.5 0.42 0.36 2 AgBArF 240 60 2×10í^ 1.3 0.61 0.63 2 AgSbF6 30 r.t. 2×10í^ 3.4 0.24 0.28 3 AgSbF6 15 r.t. 1.6×10í^ 3.48 6.75 4.420 3 AgBF4 20 r.t. 1.6×10í^ 4.92 8.48 5.981 3 AgBArF 30 r.t. 9×10í^ 0.56 0.70 0.33 a Reaction conditions: (R3%3^1L;^^^^^^^^PRO^^LQ^^^^^P/^&6D6, additive (1.0 equiv. relative to Ni pre- catalyst), 40 psig ethylene. b TOF C4 = molbutenes·molNi í^·sí^. c N.D. = not detected. Ethylene dimerization/oligomerization using aluminum co-catalyst. Alkylaluminum compounds have been commonly used as co-catalysts for homogeneous ethylene oligomerization reactions using ligated Ni halide catalyst precursors, which generally led to enhanced activities.4,52-56 Therefore, different alkylaluminums were tested as co-catalysts for our (RPBP)Ni catalysis (Table 2), and the resulting rates of ethylene dimerization are improved. Control experiments using (RPBP)H free ligand, alkylaluminums without Ni, (DME)NiBr2 with alkylaluminums, and (RPBP)H free ligand with alkylaluminums, produce no butenes or only trace amounts of butenes.10,57 When using complex 2 as the pre-catalyst in the presence of 10 equivalents of methylaluminoxane (MAO), ethylene oligomerization was achieved at room temperature with a 0.09(1) sí^ turnover frequency (TOF) for butenes (Table 2, entry 1) and 88(2)% selectivity for 1-butene (among the C4 products), which is ~900 times faster than the reaction using complex 2 with AgBF4 (Table 1, entry 3). However, the reaction products only contain ~12 wt. % of butenes (C4), and a range of linear and 2-ethyl brancheG^Į-olefins were observed from C6 to C20 (Figure 10). The identity of the Al co-catalyst influences overall catalyst activity and selectivity. For example, changing the alkylaluminum co-catalyst from MAO to EtAlCl2 results in a higher TOF (2.0(1) sí^) with an increased mass fraction of C4 olefins (~83 wt. %), while the reaction selectivity changes toward 2-butenes (Table 2, entry 2). By lowering the concentration of Ni pre-catalyst 2, a faster TOF (13.2(3) sí^) was observed with a slightly improved selectivity for 1-butene (Table 2, entry 3). Therefore, it is possible that the isomerization of 1-butene to 2-butene is a competing reaction with the ethylene dimerization/oligomerization process.
Thomas Horstemeyer Docket No.: 222117-2220 Different from using Ni pre-catalyst 2, mixing pre-catalyst 3 with MAO gave an overall slower reaction with increased selectivity toward C4 products (Table 2, entry 4). Using Et2AlCl with 3 gave a slightly faster reaction (0.18(2) sí^) while remaining selective for 1-butene (Table 2, entry 5), while the use of EtAlCl2 with complex 3 significantly enhanced the TOF (2.5(3)sí^) but changed the reaction selectivity towards 2-butenes (Table 2, entry 6). As shown in Table 2 entries 7–10, lowering the concentration of 3 improves the 1-butene selectivity as well as providing an enhanced TOF until the Ni loading is decreased WR^^^^^^^^PRO^^6LPLODUO\^^ZKHQ^XVLQJ^0$2^DV^WKH^DGGLWLYH^^GHFUHDVLQJ^WKH^1L^ORDGLQJ^IURP^ ^^^^^WR^^^^^^^^mol resulted in a higher TOF (Table 2, entry 4 vs 12). Lewis acidic AlCl3 was also used as the co-catalyst with Ni pre-catalyst 3, and gave ethylene dimerization to form 1- butene with a TOF = 0.14(0) sí^ (Table 2 entry 13). However, large amounts of Friedel– Crafts products from the reaction between toluene and ethylene/butenes were observed based on the GC-MS analysis. Therefore, due to the side reactions, the actual amount of C4 products (i.e., butenes) produced under this condition is low (8 wt. %) compared to the total consumption of ethylene. The Ni pre-catalyst (CyPBP)NiBr (4) has also been tested with MAO as an additive (Table 2, entry 14), which proved to be selective for 1-butene, but also gave 1-hexene, 2-ethyl-1-butene and 3-methyl-1-pentene as side products (Figure 10). Table 2. Screening of aluminum co-catalyst and loading of Ni pre-catalyst on ethylene oligomerization.a
Ni Loading TOF C4 b C Į-C /C ȕ-C4/C4 (%) Entrya PRO^ Additive 4 4 4 complex ^^ (sí^) wt% (%) trans Cis 1c 2 9.05 MAO 0.09(1) 12 88(2) 4(1) 7(1) 2c 2 9.05 EtAlCl2 2.0(1) 83 14(0) 56(0) 31(0) 3c 2 0.905 EtAlCl2 13.2(3) 91 46(6) 32(4) 23(2) 4 3 9.05 MAO 0.037(3) 80 88(2) 6(1) 6(1) 5 3 9.05 Et2AlCl 0.18(2) 95 79(2) 11(1) 10(1) 6 3 9.05 EtAlCl2 2.5(3) 90 16(1) 50(2) 35(2) 7 3 1.81 EtAlCl2 3.7(1) 92 30(0) 41(1) 30(0) 8 3 0.905 EtAlCl2 10.7(2) 94 30(0) 40(0) 31(0)
Thomas Horstemeyer Docket No.: 222117-2220 3 0.453 EtAlCl2 18.1(6) 92 35(3) 38(2) 28(1)0 3 0.181 EtAlCl2 3(1) 92 83(2) 10(1) 8(1)1 3 0.905 Et3Al 0.20(2) 92 94(1) 4(1) 2(0)2 3 0.905 MAO 0.18(1) 94 95(0) 3(0) 2(0)3d 3 0.905 AlCl3 0.14(0) 8 90(2) 7(1) 3(1)4 4 0.905 MAO 2.7(2) 92 97(0) 2(0) 1(0) a Reaction conditions: (RPBP)NiBr ^^^^^^^^^^^^^^^^^^^^^^^^^^^DQG^^^^^^^^PRO^^^DGGLWLYH^^^^^HTXLY^^ relative to Ni pre-FDWDO\VW^^^XVLQJ^WROXHQH^DV^WKH^VROYHQW^^^^P/^WRWDO^IRU^HDFK^UHDFWLRQ^^^HWK\OHQH^ pressure was maintained at 200 psig using a Parr gas burette system. The total consumption of ethylene was measured based on the pressure change of the gas burette and used to calculate the weight percent of butenes in all reacted ethylene (C4 wt. %). The reactions were performed at room WHPSHUDWXUH^^KRZHYHU^^WKH^DFWXDO^UHDFWLRQ^WHPSHUDWXUH^ZDV^unknown due to the exothermic nature of the reaction. Standard deviations were calculated from at least three independent experiments. b TOF C4 = molbutenes·molNi í^·sí^. c Longer chain products were detected. d Friedel–Crafts products from the reaction between toluene and ethylene/butenes were observed. Effects of alkylating reagent and Lewis acid. To further understand the role of the alkylaluminum co-catalyst, different alkylating reagents were tested with the presence of Ni pre-catalyst 2 and 3, as shown in Table 3 entries 1–7. In all cases, no or only trace amounts of butenes (< 1 TO) were observed under the reaction conditions. Among these, the reaction of the Ni bromide complex 2 with Grignard reagent has been reported to form a stable (tBuPBP)NiMe complex.50 NaBH4, a common hydride source used in the ethylene dimerization reaction,2,58 was also tested and gave no production of butenes upon combination with complex 3 (Table 3, entry 8). Therefore, we believe the ethylene dimerization and oligomerization reactions are not initiated by Ni–alkyl/hydride species such those proposed in the Cossee-Arlman type mechanism (see Introduction). Since AlCl3 with Ni pre-catalyst 3 was found to be active for the dimerization of ethylene, other Lewis acids such as BPh3, BBr3, and BF3·OEt2 were tested as an additive for the reaction (Table 3, entries 9–11). Among the results, BBr3 with complex 3 showed activity for the production of 1-butene (TOF = 0.0013 sí^), while using BF3·OEt2 as an additive gave a much faster ethylene dimerization with a TOF of 0.23(8) sí^. The observation that Lewis acids without any hydride or alkyl sources (such as AlCl3, BF3, BBr3) initiate the (RPBP)Ni catalyzed ethylene dimerization is consistent with our proposal that the catalytic ethylene oligomerization reaction is not likely initiated by a Ni–alkyl/hydride species.
Thomas Horstemeyer Docket No.: 222117-2220 Table 3. Alkylating reagents and Lewis acids.a
a Ni TOF C4 b C4/Cn Į-C4/C4 ȕ-C4/C4 (%) Entry Additive complex (sí^) (%) (%) trans Cis 1 2 EtMgBr N.D. – N.D. N.D. N.D. 2 2 MeMgBr N.D. – N.D. N.D. N.D. 3 2 MeLi N.D. – N.D. N.D. N.D. 4 2 Me2Mg N.D. – N.D. N.D. N.D. 5c 3 EtMgBr trace – trace trace Trace 6 3 MeLi N.D. – N.D. N.D. N.D. 7 3 Me2Mg N.D. – N.D. N.D. N.D. 8 3 NaBH4 N.D. – N.D. N.D. N.D. 9c,d 3 BPh3 trace – trace trace Trace 10d 3 BBr3 0.0013 > 99 86 10 4 11d 3 BF3·OEt 0.23(8) 95(1) 80(0) 10(1) 10(0) a Reaction conditions: (R3%3^1L%U^^^^^^^^PRO^^^DGGLWLYH^^^^^HTXLY^^WR^1L^SUH-FDWDO\VW^^^ XVLQJ^WROXHQH^DV^WKH^VROYHQW^^^^P/^WRWDO^IRU^HDFK^UHDFWLRQ^^^HWK\OHQH^SUHVVXUH^ZDV^ maintained at 200 psig using the Parr gas burette system. The reactions were performed at URRP^WHPSHUDWXUH^^KRZHYHU^^WKH^DFWXDO^Ueaction temperature was unknown due to the exothermic nature of the reaction. The mol% of butenes in all observed olefins (C 4/Cn) was determined by GC-MS. Standard deviations were calculated from at least three independent experiments. b TOF C4 = molbutenes·molNi í^·sí^ c The observed amounts of products were less than 1 TO. d 8VLQJ^^^^^^^^PRO^RI^1L^SUH-catalyst. Optimization of reaction parameters. Different reaction parameters such as Al/Ni ratio, Ni pre-catalyst loading, and ethylene pressure were optimized using complexes 2, 3, and 4 with MAO or EtAlCl2 as shown in Table 4. We found that in general the TOF of butenes increases with the Al/Ni ratio (Table 4, entry 1 vs 2, 3 vs 4, 6 vs 7, 10 vs 11, 13 vs 14, 15 vs 16, 18 vs 19, 20 vs 21, 24 vs 25) as well as the dilution of the Ni pre-catalyst loading (Table 4, entry 2 vs 3, 7 vs 9, 14 vs 15, 19 vs 20 vs 24). The reaction is exothermic,
Thomas Horstemeyer Docket No.: 222117-2220 as the temperature rises upon addition of ethylene gas. Therefore, a set of experiments was performed with external cooling of the VCO steel reactor using an ice bath, which resulted in a slightly faster rate and better selectivity for 1-butene compared to the reaction at room temperature without cooling (Table 4, entry 7 vs 8). This suggests that higher reaction temperatures might not be beneficial for the reaction and, instead, could potentially lead to faster isomerization of 1-butene to 2-butenes, as well as possible decomposition of the active Ni species. Decreasing the loading of Ni pre-catalyst also generates less heat during the reaction, which could partially rationalize the increase in TOF when diluting the Ni pre- catalyst. When using EtAlCl2 as the co-catalyst, increasing the ethylene pressure resulted in better selectivity for 1-butene (Table 4, entry 11 vs 12, 23 vs 24, 25 vs 26), while using MAO gave an opposite trend (Table 4, entry 4 vs 5, 16 vs 17). The difference in selectivity based on ethylene pressure is potentially rationalized by competition between ethylene dimerization, 1-butene to 2-butenes isomerization, and dimerization/oligomerization of butene upon reaction with ethylene. Using the more C4 selective co-catalyst (i.e., EtAlCl2), higher ethylene pressure suppresses 1-butene isomerization, while with the less C4 selective co-catalyst (i.e., MAO), higher ethylene pressure favors the potential dimerization/oligomerization of butene with ethylene that might consume 1-butene and 2- butene at different rates with 1-butene being converted to higher olefins more rapidly than 2- butenes, thus decreasing the 1-butene to 2-butenes ratio. For all tested conditions, complex 2 with 1000 equivalents of EtAlCl2 under 600 psig of ethylene, gave the fastest reaction which was selective for 1-butene with a TOF of 33(2) sí^ and 87(0)% selectivity (Table 4, entry 12). Whereas, complex 3 under the same conditions achieved the best overall TOF of butenes (274(34) sí^), but only 41(1)% selectivity for 1-butene (Table 4, entry 26).
a Loading C2H4 Al/Ni TOF C4 Į-C4/C4 C4/Cn TOF C6 Entry [Ni] [Al] ^^PRO^ (psig) ratio (sí^) (%) (%) (sí^) 1c 2 9.05 200 MAO 1 0.0012(1) 64(3) 20(2) 0.0004(1) 2c 2 9.05 200 MAO 10 0.09(1) 88(2) 9(1) 0.10(1) 3c 2 0.905 200 MAO 10 0.52(1) 98(0) 21(0) 0.27(1) 4c 2 0.905 200 MAO 1000 2.2(2) 93(0) 6(1) 3.0(5) 5c 2 0.905 600 MAO 1000 9(2) 80(1) 7(0) 10(3) 6c 2 9.05 200 EtAlCl2 1 0.023(2) 94(1) 28(2) 0.008(0) 7c 2 9.05 200 EtAlCl2 10 2.0(1) 14(0) 86(1) 0.29(2) 8c,d 2 9.05 200 EtAlCl2 10 2.8(5) 21(0) 85(2) 0.36(1) 9c 2 0.905 200 EtAlCl2 10 13(0) 46(6) 89(1) 0.97(6) 10c 2 0.453 200 EtAlCl2 10 1.3(2) 89(1) 47(2) 0.30(5) 11c,e 2 0.453 200 EtAlCl2 1000 45(1) 48(0) 92(0) 2.1(1) 12c,e 2 0.453 600 EtAlCl2 1000 33(2) 87(0) 94(0) 0.8(1) 13 3 9.05 200 MAO 1 0.003(0) 93(0) – N.D. 14 3 9.05 200 MAO 10 0.037(3) 88(2) >98 0.0003 15 3 0.905 200 MAO 10 0.18(1) 95(0) 96(0) 0.0003(0) 16 3 0.905 200 MAO 1000 34(3) 16(0) 89(1) 3.7(2) 17 3 0.905 600 MAO 1000 66(4) 11(0) 69(2) 23(1) 18 3 9.05 200 EtAlCl2 1 0.24(5) 69(10) 96(0) 0.01(0) 19 3 9.05 200 EtAlCl2 10 2.5(3) 16(1) 81(1) 0.46(8) 20 3 0.905 200 EtAlCl2 10 10.7(2) 30(0) 90(0) 1.1(1) 21 3 0.905 200 EtAlCl2 100 27(5) 20(1) 84(2) 4.2(6) 22e 3 0.905 600 EtAlCl2 1000 110(13) 22(1) 85(2) 15(4) 23 3 0.453 100 EtAlCl2 10 5.4(1) 22(1) 85(1) 0.8(0) 24 3 0.453 200 EtAlCl2 10 18.1(6) 35(3) 92(1) 1.3(1) 25e 3 0.453 200 EtAlCl2 1000 115(17) 18(1) 91(1) 9(2) 26e 3 0.453 600 EtAlCl2 1000 274(34) 41(1) 88(3) 30(3) 27 4 0.905 200 MAO 10 2.7(2) 97(0) 90(1) 0.29(5)
Thomas Horstemeyer Docket No.: 222117-2220 4 0.905 200 MAO 1000 22(1) 33(0) 41(3) 19(2) 4 0.905 200 EtAlCl2 10 14(1) 60(4) 83(2) 2.5(5) 4 0.905 200 EtAlCl2 1000 20(2) 40(3) 94(0) 0.9(1) a Reaction conditions: (R3%3^1L%U^^^^^^^^^^^^^^DQG^^^^^^^^PRO^^^DGGLWLYH^^^^^^^^^^^^^DQG^^^^^^HTXLY^^ to Ni pre-FDWDO\VW^^^XVLQJ^WROXHQH^DV^WKH^VROYHQW^^^^P/^WRWDO^IRU^HDFK^UHDFWLRQ^^^HWK\OHQH^SUHVVXUH^ZDV^ maintained at 100, 200 or 600 psig using the Parr gas burette system. The reactions are performed at room temperDWXUH^^KRZHYHU^^WKH^DFWXDO^UHDFWLRQ^WHPSHUDWXUH^LV^XQNQRZQ^GXH^WR^WKH^H[RWKHUPLF^QDWXUH^ of the reaction. The mol% of 1-EXWHQH^LQ^EXWHQHV^^Į-C4/C4), and butenes in all observed olefins (C4/Cn) were determined by GC-MS. N.D. = not detected. Standard deviations are calculated from at least three independent experiments. b TOF C4 = molbutenes·molNi í^·sí^ c Longer chain products were detected. d The VCO reactor was cooled with an ice bath during the reaction. e Reaction was monitored after 10 min. Comparison of previously reported Ni catalysts. Table 5 compares selected results of our newly reported catalysis with previously reported homogeneous Ni catalysts which demonstrated activity for ethylene dimerization.2,4,55-56,59-65 Although a direct comparison of previously reported catalysts is not possible since the reactions were performed under different conditions (e.g., pressure, temperature, Ni catalyst concentration, Al/Ni ratio, etc.), the comparative data provide some reasonable comparison points. The activities given in Table 5 were all converted into a commonly used unit goligomers·molNi í^·hí^ for each catalytic system. The overall TOFs given in Table 5 were calculated based on ethylene consumption, for which TOF = activity/(molar mass of C2H4) with a unit
general, most of the reported highly active Ni catalysts are supported by SHOP-type and related phosphine-sulfur-, phosphine-, nitrogen-based ligand structures. In addition to the ethylene polymerization reaction reported by the Nozaki group,51 there are only a limited number of ligand structures with a central boron center.66 As outlined in Table 5, the new RPBP ligated Ni complexes reported in this work exhibit relatively high activities for the ethylene dimerization reaction, which motivated us to better understand the reaction pathway (see below). Table 5. Comparison of previously reported homogeneous Ni catalysts for ethylene dimerization to our newly reported PBP-Ni catalysis.a Ligand Activitya TOFethyleneb Į-C4/C4 C4/Cn Temp. co-catalyst í^ ref type g/(molNi·h) (s ) (%) (%) (°C)
Thomas Horstemeyer Docket No.: 222117-2220 (P,P) EtAlCl2 2.4 × 108 2377 35 82 45 (55) (O,N,S) MAO 1.4 × 108 1411 16 90 0 (56) (N,N) Et3Al2Cl3 4.6 × 107 460 92 88 r.t. (59) (N,N,N) Et2AlCl/PPh3 4.0 × 107 391 12 92 20 (60) (N,N) MAO 1.9 × 107 190 56 90 35 (61) (P,O) None 1.9 × 107 183 99 85 40 (67) (N,N,O) MAO 1.2 × 107 119 18 83 45 (62) (P,N) EtAlCl 2 9.1 × 10 6 90 23 98 40 ( 63 ) (N,O) Et2AlCl 6.6 × 106 65 100 100 30 (64) (N,N) Et2AlCl 4.7 × 106 46 > 99 77 45 (65) (tBuP,B,P) EtAlCl2 6.9 × 106 68 87 94 r.t. this (PhP,B,P) EtAlCl2 6.5 × 107 640 41 89 r.t. work a Most of the catalysts activities in this table were originally reported in goligomers·molNi í^·hí^, thus we converted all data to the same units for comparison. b Based on ethylene consumption, for which TOF = activity/(28.05 g/mol) with the unit of molethylene·molNi í^·sí^. Isomerization of 1-butene. A set of experiments using 1-butene as the only substrate with EtAlCl2 or MAO as the co-catalyst with and without Ni pre-catalyst 2 or 3 was performed (Figure 1). Similar to the reaction using propylene as a substrate, no dimerization or oligomerization products of butenes were found based on the GC-MS analysis. While both complex 2 and 3 were able to isomerize 1-butene to 2-butenes in the presence of EtAlCl2 or MAO, control experiments using only EtAlCl2 or MAO showed much slower rates of isomerization of 1-butene to 2-butenes. Using the Ni pre-catalyst 3 approximately 10-fold faster isomerization of 1-butene to 2-butenes was observed compared to pre-catalyst 2 under the conditions using EtAlCl2, which is consistent with the observed ligand effect on 1- vs 2- butene selectivity of the ethylene dimerization reactions (see Table 1, and Table 4, entry 6 vs 18, 9 vs 21, 10 vs 24, 11 vs 25, 12 vs 26). As noted above, this ligand effect (i.e., 2-butenes vs. 1-butene selectivity as a function of identity of PBP ligand) can be rationalized by the presence of a more sterically hindered tBu group in complex 2 inhibiting 1-butene coordination, and thus retarding the rate of 1-butene isomerization. In addition, using EtAlCl2 with and without Ni pre-catalyst gave a much faster isomerization compared to MAO, which is also consistent with the observed difference in 1- vs 2-butene selectivity when using EtAlCl2 or MAO as additive (see Table 4, entries 2 vs 7, 3 vs 9, 13 vs 18, 14 vs 19, 15 vs
Thomas Horstemeyer Docket No.: 222117-2220 DFT analysis on the reaction mechanism. The aforementioned experimental data point to a mechanism for which the [(RPBP)Ni]+ fragment plays a fundamental role in the dimerization of ethylene to yield 1-butene. Indeed, control experiments revealed the participation of both the PBP ligand and nickel in the process, and stoichiometric experiments ruled out the likely involvement of nickel acetate, hydride, or alkyl species. Therefore, we conducted DFT studies using cationic complex 5, produced from the reaction between bromide species 2 and a halide abstractor (e.g., AgBF4, NaBArF, AgBArF, etc.). Calculations were carried out at the PBE0/def2TZVP/def2QZVP level of theory, including Grimme’s D3 dispersion correction (PBE0-D3, see SI for information and references), using 5 and ethylene as the energy reference. Scheme 3, Figure 11, illustrates halide abstraction from complex 2 to give cationic complex 5. Coordination of one ethylene molecule to the vacant position of [(tBuPBP)Ni]+ (5) to give [(tBu3%3^1L^^2-C2H4)]+ (5·C2H4) LV^LVRHQHUJHWLF^^í^^^^^NFDO^PRO-1) to the reactants. From this point, several mechanistic scenarios were considered, most of which afforded kinetic barriers too energy-demanding to overcome experimentally (energy profiles for the energetically inaccessible pathways can be found in the Supporting Information). Activation of a C–+^ERQG^RI^ERXQG^HWK\OHQH^^ǻG > 50 kcal molí^) of 5·C2H4 gave Ni–vinyl and B–H fragments in a less thermodynamically stable geometry than the initial cationic Ni–HWK\OHQH^ʌ^ complex (23.4 kcal molí^ difference). Including weakly coordinating anions such as BF4 í in the calculations led to even higher Gibbs free energy values. The addition of a free ethylene molecule to the coordinated ethylene of 5·C2H4 was also computed, based on the study by Bernardi, Bottoni et al.21 This resulted in the desired 5·1-butene FRPSOH[^^í^^^^^NFDO^PROí^), yet at the expense of very high energy transition states.68 Exploratory calculations involving [2+2] cycloaddition pathways did not lead to chemically meaningful results. Finally, dissociation of one of the phosphine ligands or coordination of the ethylene molecule across the Ni–B bond gave energy barriers above 30 kcal molí^ along with thermodynamically unstable products. However, coordination of a second ethylene molecule to 5·C2H4 opened the door to a new ethylene dimerization mechanism involving participation of the PBP ligand. Figure 2 shows a calculated pathway for (RPBP)Ni-mediated positioning of two ethylene molecules for subsequent C–C coupling. Ethylene binding to give complex 5·(C2H4)2 is thermodynamically unfavorable (18.5 kcal molí^ higher than 5·C2H4), as depicted in Figure 2. This is in line with our previous studies on H2 activation by neutral,
Thomas Horstemeyer Docket No.: 222117-2220 square planar Ni(II) complexes,50,69 for which the filled dz 2 orbital on nickel gave rise to weak ı-H2 complexes.70 Indeed, 5·(C2H4)2 exhibits very little C=C bond elongation upon binding (1.36 Å vs 1.33 Å in free ethylene). Nonetheless, molecular orbital analysis of ethylene and 5·C2H4 (Figure 3) point to potential orbital overlap involving the PBP ligand {HOMO (5·C2H4) Æ LUMO (ethylene)} that can lead to ethylene functionalization. In fact, this second ethylene molecule binds across the Ni–B bond in transition state TS1 (23.2 kcal molí^) to form a 4-membered borametallacycle, simultaneously promoting dissociation of one of the phosphine ligands from the metal center, as observed in the product 6 (Figure 2). Complex 5 is 16.2 kcal molí^^above the reactants, which suggests the formation of 5 is possibly reversible. However, the rest of the kinetic barriers are lower than TS1, and the high thermodynamic stability of the product makes the overall process energetically downhill and favorable towards the formation of the experimentally observed 1-butene (see below). The calculated phosphine dissociation is probably due to steric clash between the ethylene moieties and the tert-butyl substituents on the phosphorus atom. In fact, both ethylene ligands in 6 are oriented towards the space previously occupied by the phosphine ligand (Figure 2, inset). The short C···C distance (2.37 Å) observed for the two closer carbon atoms suggests preorganization of both ethylene fragments for subsequent C–C coupling. The C–C bond formation between two ethylene ligands is calculated to proceed through TS2 (17.1 kcal molí^), located only 0.9 kcal molí^ higher than complex 6 (Figure 4). The next intermediate after TS2 (species 7, 13.9 kcal molí^) contains a six-membered B–Cį–CȖ–Cȕ–CĮ–Ni ring, with C–C distances ranging from 1.50 to 1.67 Å. Although the distance arrangement might suggest some butadiene character, these C–C bonds are longer than those observed in 1,3- butadiene (1.34–1.45 Å).71 From complex 7, numerous hydrogen atom migrations have been explored to form either B–H or new C–H bonds, giving too energy demandiQJ^^ǻG > 30 kcal molí^) kinetic barriers. However, the Cȕ^atom can orient one of its hydrogen atoms closer to the metal center with minimal energy cost (TS3 = 12.8 kcal molí^), in order to achieve a VXLWDEOH^VWUXFWXUH^IRU^D^ȕ-hydride elimination step. The outcome of this rearrangement is complex 8, which exhibits an agostic interaction72 through the Cȕ–H bond (Ni–H = 1.78 Å, Ni–C = 2.11 Å, Ni–H–C = 89.2°), located trans to the bound phosphine ligand. Although this complex is rather low in Gibbs free energy (7.9 kcal molí^), we found a different, more energy-demanding isomer (8', 19.7 kcal molí^) where the Cȕ–H bond and the bound phosphine are in a cis orientation, and the 3c-2e interaction exhibits a much shorter Ni–H bond (1.55 Å), with similar Ni–C (2.11 Å) and Ni–H–C (96.9°) metrics to those observed for
Thomas Horstemeyer Docket No.: 222117-2220 7. Complex 8' SURFHHGV^WR^D^ȕ-H elimination transition state (TS4) with a free energy of activation of only 0.3 kcal/mol. The geometry of 8' is very similar to that observed for TS4 (early transition state), which might explain why the firsW^ȕ-hydride elimination step is only 0.3 kcal molí^ higher in energy (Figure 5). After TS4, intermediate 9 (12.4 kcal molí^) contains the newly formed C=C double bond (C=C distance = 1.36 Å) bound to nickel, along with coordination of one of the phosphines and the new hydride ligand. In addition, the fourth Ni-coordination position LV^VWDELOL]HG^E\^D^ZHDN^ı^LQWHUDFWLRQ^ZLWK^WKH^%–Cį bond (B–Ni = 2.76 Å C–Ni = 2.48 Å). Although one might think that 1-butene is practically formed, exploratory calculations involving hydride transfer to Cį or B to release the experimentally observed product led to high (> 30 kcal molí^) energy barriers. Nevertheless, TS5 (11.6 kcal molí^) was found, which reveals the stretch of the B–C
Ni interaction along its imaginary frequency, giving rise to species 10 (10.8 kcal molí^). In this geometry, an agostic interaction through the Cį–H bond is observed (Ni–H = 1.88 Å, Ni–C = 2.28 Å, Ni–H–C = 95.5°) along with shorter Ni···C distances (ranging from 0.05 to 0.2 Å) for all the carbon atoms coming from the ethylene fragments. Next, hydride transfer to CĮ^occurs via TS6, located 15.6 kcal molí^ above the energy reference. This hydride transfer process leads to intermediate 11 (14.8 kcal molí^), which contains a new nickel-carbon bond (Ni–Cȕ^= 1.89 Å) and two agostic interactions: the previous one observed for the Cį–H bond, and another for one of the CĮ–H bonds of the new CH3 group. In a similar fashion to intermediates 8 and 8', isomer 11' was found, where both agostic interactions are replaced by two different ones: one C–H bond from one of the tert- butyl groups of the bound phosphine, and a C–H bond from CȖ. This bonding arrangement is DJDLQ^VXLWDEOH^IRU^D^ȕ-hydride elimination step, which indeed proceeds through TS7, located only 0.6 kcal molí^ above 11'. This event leads to the formation of an internal double bond in the tetracarbon chain of complex 12 (10.4 kcal molí^). From this point, it seems reasonable that the hydride ligand can be transferred to Cį^to rationalize the formation of trans 2-butene. However, relaxed potential energy scan calculations revealed hydride transfer to CȖ instead (i.e., formation of intermediate 11), probably due to its closer proximity and the relative stability of such geometry. Complex 12 features a nickel center with a T-shaped geometry for which the hydride ligand is pointing to the boryl fragment. Therefore, it needs to orbit around the metal in order to give 1-butene. This orbiting movement requires negligible energy (TS8, 10.6 kcal molí^) and places the hydride ligand close to Cȕ (H···Cȕ^= 2.53 Å, intermediate 13, Figure 6) for
Thomas Horstemeyer Docket No.: 222117-2220 subsequent transfer, which takes place via TS9 (14.6 kcal molí^). Interestingly, this transition state also involves the formation of the Cį=CȖ double bond and the cleavage of the B–Cį bond, giving species 14. In this intermediate, the nickel atom adopts a distorted square planar geometry in which 1-butene is bound to nickel through the double bond and one agostic interaction. Thus, phosphine coordination can easily occur (TS10, 6.6 kcal molí^), displacing the C–H bond and regenerating the pincer scaffold in 5·1-butene ^í^^^^^NFDO^PROí^). Finally, regeneration of cationic complex 5 and dissociation of the 1-butene is the most stable step in WKH^HQWLUH^SURFHVV^^DV^H[SHFWHG^^í^^^^^NFDO^PROí^). This proposed mechanism highlights the role of the PBP ligand in the catalytic dimerization of ethylene. First, its tridentate nature allows the approach of one equivalent of ethylene to the vacant position of a square planar, cationic Ni(II) complex. Then, the boryl fragment facilitates coordination of a second ethylene molecule, and serves as an anchoring point for one of the ends of the tetracarbon chain, allowing hydrogen atom rearrangement throughout the entire cycle while keeping the substrate bound to the catalyst. Lastly, the hemilabile character of the phosphine groups on the pincer scaffold is instrumental for the development of the elementary steps in the cycle, since they can dissociate when needed to create a vacant position in the coordination sphere, which they can also stabilize by means of agostic interactions through the substituents on phosphorus. Summary and Conclusions We have demonstrated that RPBP-Ni complexes are active catalysts for ethylene dimerization/oligomerization. Our studies revealed that the ethylene dimerization is generally selective for the formation of terminal 1-butene, and that the features of catalysis are dependent on ligand identity. The reactions proceed by using (tBuPBP)NiOAc (1) without co- catalyst, as well as mixing (RPBP)NiBr (2 or 3) with Ag+ or Na+ salts, alkylaluminum, or other Lewis acids (e.g., BF3, BBr3, and AlCl3). The (PhPBP)Ni complex 3 shows significant activity for the production of butenes with a TOF up to 274(34) molbutenes·molNi í^·sí^ (41(1)% selective for 1-butene), while the (tBuPBP)Ni complex 2 shows good selectivity for 1-butene with a TOF up to 33(2) molbutenes·molNi í^·sí^ (87(0)% selective for 1-butene). Experimental evidence is consistent with the reaction likely being initiated by cationic [(RPBP)Ni]+ species instead of Ni–alkyl/hydride complexes.
Thomas Horstemeyer Docket No.: 222117-2220 Experimental Section General information. All reactions were performed under a dinitrogen or argon atmosphere using Schlenk line techniques or inside a dinitrogen filled glovebox unless specified otherwise. GC-MS was performed using a Shimadzu GCMS-QP2020 NX with a 30 m × 0.25 mm Rt-Q-Bond capillary column with 8 μm film thickness and a 30 m × 0.25 mm Rxi-5ms capillary column with 0.25 μm film thickness using electron impact ionization method. All NMR reactions were performed using Wilmad medium wall precision low pressure/vacuum (LPV) NMR tubes and pressurized with ethylene or propylene using a high- pressure line. Toluene was dried using a sodium-benzophenone/ketyl still under a dinitrogen atmosphere and stored inside a glovebox. Tetrahydrofuran and diethyl ether were dried via a potassium-benzophenone/ketyl still under a dinitrogen atmosphere and stored over activated 4Å molecular sieves inside a glovebox. Benzene, pentane, and methylene chloride were dried using a solvent purification system with activated alumina and stored under activated 3Å molecular sieves inside a dinitrogen filled glovebox. Hexanes was dried using 4Å molecular sieves. Toluene-d8 and benzene-d6 were dried and stored over activated 3Å molecular sieves inside a glovebox. All other chemicals were purchased from commercial sources and used as received. NMR spectra were recorded on Varian VNMRS 600 MHz or 500 MHz spectrometer or a Bruker Avance III 800 MHz spectrometer. All reported chemical shifts were referenced to residual 1H resonances (1H NMR) or 13C{1H} resonances (13C{1H} NMR). 1H NMR: benzene-d6 ^^^^^SSP^^WROXHQH-d87.09 ppm. 13C NMR: benzene-d6 ^^^^^^SSP^^WROXHQH-d8 137.5 ppm.73 The 19F 105^VSHFWUD^ZHUH^UHIHUHQFHG^WR^KH[DIOXRUREHQ]HQH^į^í^^^^^^SSP^DV^ an external standard.31P{1H} NMR spectra were referenced to H3PO4 į^^^^^SSP^DV^DQ^ external standard. Elemental analyses were performed by the University of Virginia Chemistry Department Elemental Analysis Facility. General procedure for in Situ 1H NMR Studies of ethylene dimerization. Described here is a representative procedure for our NMR studies. Inside a dry dinitrogen filled glovebox, a stock solution of internal standard hexamethyldisiOR[DQH^^+0'62^^^^^^/^^ 0.0471 mmol) in 10 mL of benzene-d6 was made using a volumetric flask. A stock solution of Ni pre-FDWDO\VW^^^^^^^^PRO^^LQ^^^P/^RI^WKH^+0'62^EHQ]HQH-d6 solution was made to ensure reproducible concentration of the Ni complex (9.05 mmol^/^^^7KH^DGGLWLYH^^^^^^^^PRO^^^^ equiv. relative to Ni pre-catalyst) was added to the stock solution of Ni pre-catalyst. After
Thomas Horstemeyer Docket No.: 222117-2220 stirring, 0.5 mL of the mixture was syringed into a medium-wall LPV NMR tubes. Then, the LPV NMR tubes were pressurized with 40 psig of ethylene. Quantitative
NMR experiments were performed using HMDSO as the internal standard. The LPV NMR tube was held at room temperature or heated in an oil bath at a specific temperature, then the integration changes of the 1-butene, trans- and cis-2-butene signals were measured at time intervals by experiments. General procedure for high-pressure reactions under constant ethylene pressure. All high-pressure reactions were performed using customized steel reactors (VCO) with a fixed volume (300 cm3) high pressure gas burette system. The connection between reactor and the gas burette system was custom built with the function to place all metal tubing under vacuum to prevent air or moisture contamination of the VCO reactor. The following is a representative procedure for our high-pressure studies. The high-pressure gas burette system was evacuated and refilled with pure ethylene (99.9%, 3.0 PL) using a high-pressure line. Inside a dry dinitrogen filled glovebox, the Ni pre-FDWDO\VW^^^^^^^^PRO^^ZDV^SODFHG^LQ^WKH^ VCO reactor with a glass insert, followed by addition of dried toluene (1 mL total, the actual volume depends on the amount of additive used) and additives (equiv. relative to Ni pre- catalyst). When using lower Ni pre-catalyst loading, a stock solution of Ni pre-catalyst in dry toluene was made to ensure reproducible concentrations of Ni complex. Then the VCO reactor was sealed and connected to the high-pressure gas burette system prefilled with ethylene. The connection metal tubing was evacuated and then charged with ethylene, and this process was repeated three times. The output ethylene pressure was set to 200 psig (or 600 psig under some conditions). Then the valve connected to the VCO reactor was opened, and the pressure on the gas burette was recorded. After specific reaction time (10 or 20 min), the valve connected to the VCO reactor was closed and the pressure on the gas burette was recorded, followed by placing the VCO reactor into a dry ice/acetone bath. The pressure change of the gas burette was used to calculate ethylene consumption using the ideal gas law. After the reactor was sufficiently cooled, the top pressure was slowly released, followed by adding 1 mL of toluene (undried) to the reactor. For the conditions using 1000 equivalents of DON\ODOXPLQXP^^^^GURS^RI^ZDWHU^ZDV^DGGHG^^7KHQ^^^^^^/^RI^WHWUDK\GURIXUDQ^ZHUH^V\ULQJHG^ into the reactor as the standard for GC-MS analysis. Butenes were quantified using a Rt-Q- Bond column, and the remainder of the olefins was quantified using with a Rxi-5ms column. Synthesis and characterization of Ni complexes. (tBuPBP)NiOAc (1),49 and (tBuPBP)NiBr (2),50 and (PhPBP)H33 were synthesized based on published procedures.
Thomas Horstemeyer Docket No.: 222117-2220 (PhPBP)NiBr (3). To a solution of (DME)NiBr2 (240 mg, 0.778 mmol) in 15 mL of dry toluene under Ar atmosphere, a solution of (PhPBP)H (400 mg, 0.778 mmol) and Et3N ^^^^^^P/^^^^^^^^PPRO^^LQ^^^^P/^RI^GU\^WROXHQH^ZDV^FDQQXODWHG^VORZO\^DW^í^^^^&^^7KH^ reaction mixture was allowed to warm to room temperature slowly and stirred overnight. The solvent was removed in vacuo, then the solid residue was washed with cold pentane ^í^^^^&^^ 5 mL × 2). The resulting solid was extracted using dry toluene, and the solution was dried under vacuum to isolate the product as an orange-yellow solid that is sensitive to moisture and oxygen (390 mg, 78% isolated yield).
1H NMR (800 MHz, benzene-d6^^į^^^^^^^GG^YW^^1JH,H = 7 Hz, 3JH,H = 2 Hz, 8H), 7.15 (AA'XX' dd, partially overlapped with benzene-d6, 2H), 7.01 – 6.96 (m, 12H), 6.90 (AA'XX' dd, JAX = 7.7 Hz, JAX' = 1.2 Hz, JAA' = 0.4 Hz, JXX' = 7.6 Hz, 2H), 4.00 (vt, N = 4.8 Hz, 4H, NCH2P). 31P{1H} NMR (243 MHz, benzene-d6^^į^^^^^^^^V^^ 13C{1H} NMR (201 MHz, benzene-d6^^į^ 139.2 (vt, N = 18 Hz), 133.7 (vt, N = 12 Hz), 132.7 (vt, N = 38 Hz), 130.4, 128.8 (vt, N = 9 Hz), 119.4, 109.7, 49.1 (vt, N = 44 Hz, PCH2). Anal. Calcd for C32H28BBrN2NiP2^^&^^^^^^^^^ +^^^^^^^^1^^^^^^^^)RXQG^^&^^^^^^^^^+^^^^^^^^1^^^^^^^ (CyPBP)NiBr (4). A solution of (CyPBP)H ligand (500 mg, 0.928 mmol) in toluene (10 mL) and Et31^^^^^^^^P/^^^^^^^PPRO^^DW^í^^^^&^ZDV^WUDQVIHUUHG^YLD^FDQQXOD^WR^D^ suspension of (DME)NiBr2 (286.4 mg, 0.928 mmol) in toluene (10 mL) at the same temperature. The resulting suspension was allowed to warm to room temperature, and it was stirred at the same temperature for 18 h, after which the stirring was stopped, and the dark yellow solution decanted to a Schlenk flask by using a cannula with a double filter paper. The remaining solid was extracted with toluene (10 mL × 3), and the combined organic phase was evaporated under vacuum to give Ni–Br as a brown solid (578 mg, 0.854 mmol, 92% yield). X-Ray quality crystals can be obtained by diffusion of pentane into a toluene solution of 4.
1H NMR (400 MHz, benzene-d6): į^7.18 (AA'XX' dd, partially overlapped with benzene-d6, 2H, aromatic CH), 7.01 (AA'XX' dd, JAX = 7.6 Hz, JAX' = 1.3 Hz, JAA' = 0.5 Hz, JXX' = 7.6 Hz, 2H, aromatic CH), 3.41 (vt, N = 4.2 Hz, 4H, NCH2P), 2.30 (m, 4 H, CH2), 2.19
Thomas Horstemeyer Docket No.: 222117-2220 (quint vt, 3JHH = 2.9 Hz, N = 24.6 Hz, 4H, CH-P), 1.80 (m, 4 H, CH2), 1.70 (m, 4 H, CH2), 1.59 (m, 12 H, CH2), 1.36 (m, 4 H, CH2), 1.22 (m, 4 H, CH2), 1.08 (m, 8 H, CH2). 31P{1H} NMR (161 MHz, benzene-d6) į 66.68 (s). 11B{1H} NMR (128 MHz, benzene-d6): į 40.3 (br s, boryl). 13C{1H} NMR (100 MHz, benzene-d6): į^139.7 (vt, N = 16 Hz, ligand aromatic Cq), 119.0 (ligand aromatic CH), 109.3 (ligand aromatic CH), 40.5 (vt, N = 37 Hz, NCH2P), 33.9 (vt, N = 19. Hz, C1), 29.2 (C2, C6), 28.8, 27.1 – 27.3 (m, C3,C5), 26.5 (C4). Anal. Calcd. for C32H52BBrN2NiP2^^&^^^^^^^^^+^^^^^^^^1^^^^^^^^)RXQG^^&^^^^^^^^^+^^^^^^^^1^^^^^^^ References 1. 3LOODL^^6^^0^^^5DYLQGUDQDWKDQ^^0^^^6LYDUDP^^6^^^'LPHUL]DWLRQ^RI^HWK\OHQH^DQG^ propylene catalyzed by transition-metal complexes. Chem. Rev.1986, 86, 353-399. doi: 10.1021/cr00072a004 2. Olivier-%RXUELJRX^^+^^ %UHXLO^^3^^$^^5^^^0DJQD^^/^^^0LFKHO^^7^^^(VSDGD^3DVWRU^^0^^)^^^ Delcroix, D., Nickel Catalyzed Olefin Oligomerization and Dimerization. Chem. Rev. 2020, 120, 7919-7983. doi: 10.1021/acs.chemrev.0c00076 3. ,WWHO^^6^^'^^^-RKQVRQ^^/^^.^^^%URRNKDUW^^0^^^/DWH-Metal Catalysts for Ethylene Homo- and Copolymerization. Chem. Rev. 2000, 100, 1169-1204. doi: 10.1021/cr9804644 4. %HNPXNKDPHGRY^^*^^(^^^6XNKRY^^$^^9^^^.XFKNDHY^^$^^0^^^<DNKYDURY^^'^^*^^^1L- Based Complexes in Selective Ethylene Oligomerization Processes. Catalysts 2020, 10. doi: 10.3390/catal10050498 5. Breuil, P.-$^^5^^^0DJQD^^/^^^2OLYLHU-Bourbigou, H., Role of Homogeneous Catalysis in Oligomerization of Olefins : Focus on Selected Examples Based on Group 4 to Group 10 Transition Metal Complexes. Catal. Lett. 2015, 145, 173-192. doi: 10.1007/s10562-014- 1451-x 6. IHS Chemicals, Chemical economics handbook: linear alphaolefins, February 2020 7. =LHJOHU^^.^^^*HOOHUW^^+^^^+RO]NDPS^^(^^^:LONH^^*^^^(QWGHFNXQJ^GHV^1LFNHO^(IIHNWV^^ Brennst.-Chem. 1954, 35, 321. doi: 8. )LVFKHU^^.^^^-RQDV^^.^^^0LVEDFK^^3^^^6WDEED^^5^^^:LONH^^*^^^7KH^³1LFNHO^(IIHFW´^^ Angew. Chem. Int. Ed. 1973, 12, 943-953. doi: 10.1002/anie.197309431 9. McGuinness, D. S., Olefin Oligomerization via Metallacycles: Dimerization, Trimerization, Tetramerization, and Beyond. Chem. Rev.2011, 111, 2321-2341. doi: 10.1021/cr100217q
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Thomas Horstemeyer Docket No.: 222117-2220 32. 6HJDZD^^<^^^<DPDVKLWD^^0^^^1R]DNL^^.^^^6\QWKHVHV^RI^3%3^3LQFHU^,ULGLXP^&RPSOH[HV^^ A Supporting Boryl Ligand. J. Am. Chem. Soc. 2009, 131, 9201-9203. doi: 10.1021/ja9037092 33. 6HJDZD^^<^^^<DPDVKLWD^^0^^^1R]DNL^^.^^^'LSKHQ\OSKRVSKLQR- or Dicyclohexylphosphino-Tethered Boryl Pincer Ligands: Syntheses of PBP Iridium(III) Complexes and Their &RQYHUVLRQ^WR^,ULGLXPí(WK\OHQH^&RPSOH[HV^^Organometallics 2009, 28, 6234-6242. doi: 10.1021/om9006455 34. +LOO^^$^^)^^^/HH^^6^^%^^^3DUN^^-^^^6KDQJ^^5^^^:LOOLV^^$^^&^^^$QDORJLHV^EHWZHHQ^ Metallaboratranes, Triboronates, and Boron Pincer Ligand Complexes. Organometallics 2010, 29, 5661-5669. doi: 10.1021/om100557q 35. 2JDZD^^+^^^<DPDVKLWD^^0^^^7ULDO^IRU^DQWL-Markovnikov Hydration of 1-Decene Using Platinum Complexes Bearing a PBP Pincer Ligand, Inducing Alkene Isomerization and Decomposition of PBP Ligand. Chem. Lett. 2014, 43, 664-666. doi: 10.1246/cl.131208 36. 0F4XHHQ^^&^^0^^$^^^+LOO^^$^^)^^^6KDUPD^^0^^^6LQJK^^6^^.^^^:DUG^^-^^6^^^:LOOLV^^$^^&^^^ Young, R. D., Synthesis and reactivity of osmium and ruthenium PBP–LXL boryl pincer complexes. Polyhedron 2016, 120, 185-195. doi: 10.1016/j.poly.2016.05.041 37. 2JDZD^^+^^^<DPDVKLWD^^0^^^3ODWLQXP^FRPSOH[HV^EHDULQJ^D^ERURQ-based PBP pincer ligand: synthesis, structure, and application as a catalyst for hydrosilylation of 1-decene. Dalton Trans. 2013, 42, 625-629. doi: 10.1039/c2dt31892j 38. +DVHJDZD^^0^^^6HJDZD^^<^^^<DPDVKLWD^^0^^^1R]DNL^^.^^^,VRODWLRQ^RI^D^3%3-Pincer Rhodium Complex Stabilized by an Intermolecular C---+^ı Coordination as the Fourth Ligand. Angew. Chem. Int. Ed. 2012, 51, 6956-6960. doi: doi:10.1002/anie.201201916 39. )DQJ^^)^^^;XH^^0^^0^^^'LQJ^^0^^^=KDQJ^^-^^^/L^^6^^^&KHQ^^;^^^7KH^6WDELOLW\^RI^ 'LSKRVSKLQR^%RU\O^3%3^3LQFHU^%DFNERQH^^3%3^WR^323^/LJDQG^+\GURO\VLV^^Chemistry – An Asian Journal 2021, 16, 2489-2494. doi: 10.1002/asia.202100690 40. Lin, T.-3^^^3HWHUV^^-^^&^^^%RU\O-Mediated Reversible H2 Activation at Cobalt: Catalytic Hydrogenation, Dehydrogenation, and Transfer Hydrogenation. J. Am. Chem. Soc. 2013, 135, 15310-15313. doi: 10.1021/ja408397v 41. 'LQJ^^<^^^0D^^4^-4^^^.DQJ^^-^^^=KDQJ^^-^^^/L^^6^^^&KHQ^^;^^^3DOODGLXP^,,^^FRPSOH[HV^ supported by PBP and POCOP pincer ligands: a comparison of their structure, properties and catalytic activity. Dalton Trans. 2019, 48, 17633-17643. doi: 10.1039/c9dt03954f 42. 7DQRXH^^.^^^<DPDVKLWD^^0^^^6\QWhesis of Pincer Iridium Complexes Bearing a Boron Atom and iPr-Substituted Phosphorus Atoms: Application to Catalytic Transfer
Thomas Horstemeyer Docket No.: 222117-2220 Dehydrogenation of Alkanes. Organometallics 2015, 34, 4011-4017. doi: 10.1021/acs.organomet.5b00376 43. +LOO^^$^^)^^^0F4XHHQ^^&^^M. A., Arrested B–H Activation en Route to Installation of a PBP Pincer Ligand on Ruthenium and Osmium. Organometallics 2014, 33, 1977-1985. doi: 10.1021/om5001106 44. 0L\DGD^^7^^^<DPDVKLWD^^0^^^2[\JHQDWLRQ^RI^D^5XWKHQLXP^&RPSOH[^%HDULQJ^D^3%3- Pincer Ligand Inducing the Formation of a Boronato Ligand with a Weak Ru–O Bond. Organometallics 2013, 32, 5281-5284. doi: 10.1021/om400915x 45. +D\DVKL^^6^^^0XUD\DPD^^7^^^.XVXPRWR^^6^^^1R]DNL^^.^^^3LQFHU^6XSSRUWHG^ Perfluororhodacyclopentanes: High Nucleophilicity of WKH^0í&F Bond. Angew. Chem. Int. Ed. 2022. doi: 10.1002/anie.202207760 46. Lin, T.-3^^^3HWHUV^^-^^&^^^%RU\O–Metal Bonds Facilitate Cobalt/Nickel-Catalyzed Olefin Hydrogenation. J. Am. Chem. Soc.2014, 136, 13672-13683. doi: 10.1021/ja504667f 47. 5tRV^^3^^^&XUDGR^^1^^^/ySH]-6HUUDQR^^-^^^5RGUtJXH]^^$^^^6HOHFWLYH^UHGXFWLRQ^RI^FDUERQ^ dioxide to bis(silyl)acetal catalyzed by a PBP-supported nickel complex. Chem. Commun. 2016, 52, 2114-2117. doi: 10.1039/C5CC09650B 48. 5tRV^^3^^^5RGUtJXH]^^$^^^/ySH]-6HUUDQR^^-^^^Mechanistic Studies on the Selective Reduction of CO2 to the Aldehyde Level by a Bis(phosphino)boryl (PBP)-Supported Nickel Complex. ACS Catal. 2016, 6, 5715-5723. doi: 10.1021/acscatal.6b01715 49. 'H]LHO^^$^^3^^^(VSLQRVD^^0^^5^^^3DYORYLF^^/^^^&KDUERQHDX^^'^^-^^^+D]DUL^^1^^^+RSPDQQ^^ .^^+^^^0HUFDGR^^%^^4^^^/LJDQG^DQG^VROYHQW^HIIHFWV^RQ^&22 insertion into group 10 metal alkyl bonds. Chem. Sci. 2022, 13, 2391-^^^^^^GRL^^^^^^^^^^G^VF^^^^^G^^&RPSOH[^1 has been prepared by us following a different procedure which will be published as part of an forthcoming paper. 50. &XUDGR^^1^^^0D\D^^&^^^/ySH]-6HUUDQR^^-^^^5RGUtJXH]^^$^^^%RU\O-assisted hydrogenolysis of a nickel–methyl bond. Chem. Commun. 2014, 50, 15718-15721. doi: 10.1039/C4CC07616H 51. 6HLGHO^^)^^:^^^1R]DNL^^.^^^$^1L^^ı-Borane Complex Bearing a Rigid Bidentate Borane/Phosphine Ligand: Boryl Complex Formation by Oxidative Dehydrochloroborylation and Catalytic Activity for Ethylene Polymerization. Angew. Chem. Int. Ed. 2022, 61, e202111691. doi: 10.1002/anie.202111691
Thomas Horstemeyer Docket No.: 222117-2220 52. Fontaine, F.-*^^^=DUJDULDQ^^'^^^0H2AlCH2PMe2: A New, Bifunctional Cocatalyst for the Ni(II)-Catalyzed Oligomerization of PhSiH3. J. Am. Chem. Soc. 2004, 126, 8786-8794. doi: 10.1021/ja048911m 53. &KDQGUDQ^^'^^^%\HRQ^^6^^-^^^6XK^^+^^^.LP^^,^^^(IIHFW^RI^,RQ-Pair Strength on Ethylene Oligomerization by Divalent Nickel Complexes. Catal. Lett. 2013, 143, 717-722. doi: 10.1007/s10562-013-1021-7 54. 'UHVFK^^/^^&^^^GH^$UD~MR^^%^^%^^^&DVDJUDQGH^ 2^^G^^/^^^6WLHOHU^^5^^^$^QRYHO^FODVV^RI^ nickel(ii) complexes containing selenium-based bidentate ligands applied in ethylene oligomerization. RSC Advances 2016, 6, 104338-104344. doi: 10.1039/C6RA18987C 55. +XDQJ^^<^^^=KDQJ^^/^^^:HL^^:^^^$ODP^^)^^^-LDQJ^^T., Nickel-based ethylene oligomerization catalysts supported by PNSiP ligands. Phosphorus, Sulfur Silicon Relat. Elem. 2018, 193, 363-368. doi: 10.1080/10426507.2018.1424157 56. ;X^^&^^^6KHQ^^4^^^6XQ^^;^^^7DQJ^^<^^^6\QWKHVLV^^&KDUDFWHUL]DWLRQ^^DQG^+LJKO\^Selective Ethylene Dimerization to 1-%XWHQH^RI^>2í1;@1L^,,^^&RPSOH[HV^^Chin. J. Chem . 2012, 30, 1105-1113. doi: 10.1002/cjoc.201100443 57. Ziegler, K., Aluminium-organische Synthese im Bereich olefinischer Kohlenwasserstoffe. Angew. Chem. 1952, 64, 323-329. doi: 10.1002/ange.19520641202 58. +RODK^^'^^*^^^+XJKHV^^$^^1^^^+XL^^%^^&^^^.DQ^^&^-T., Production of Ni(I) complexes from reactions between Ni(II) and NaBH4 in the presence of triphenylphosphine and some bidentate phosphines. Can. J. Chem. 1978, 56, 2552-2559. doi: 10.1139/v78-419 59. &KDQGUDQ^^'^^^/HH^^.^^0^^^&KDQJ^^+^^&^^^6RQJ^^*^^<^^^/HH^^-^-(^^^6XK^^+^^^.LP^^,^^^ Ni(II) complexes with ligands derived from phenylpyridine, active for selective dimerization and trimerization of ethylene. J. Organomet. Chem. 2012, 718, 8-13. doi: 10.1016/j.jorganchem.2012.08.005 60. =KDQJ^^0^^^=KDQJ^^6^^^+DR^^3^^^-LH^^6^^^6XQ^^:^-+^^^/L^^3^^^/X^^;^^^1LFNHO^&RPSOH[HV^ Bearing 2-(Benzimidazol-2-yl)-1,10-phenanthrolines: Synthesis, Characterization and Their Catalytic Behavior Toward Ethylene Oligomerization. Eur. J. Inorg. Chem. 2007, 2007, 3816-3826. doi: 10.1002/ejic.200700392 61. $QWRQRY^^$^^$^^^6HPLNROHQRYD^^1^^9^^^6RVKQLNRY^^,^^(^^^7DOVL^^(^^3^^^%U\OLDNRY^^.^^3^^^ Selective Ethylene Dimerization into 2-Butenes Using Homogeneous and Supported Nickel(II) 2-Iminopyridine Catalysts. Top. Catal. 2020, 63, 222-228. doi: 10.1007/s11244- 019-01208-8
Thomas Horstemeyer Docket No.: 222117-2220 62. %RXGLHU^^$^^^%UHXLO^^3^-$^^5^^^0DJQD^^/^^^2OLYLHU-%RXUELJRX^^+^^^%UDXQVWHLQ^^3^^^ Nickel(II) complexes with imino-imidazole chelating ligands bearing pendant donor groups (SR, OR, NR2, PR2) as precatalysts in ethylene oligomerization. J. Organomet. Chem. 2012, 718, 31-37. doi: 10.1016/j.jorganchem.2012.07.044 63. )HQJ^^&^^^=KRX^^6^^^:DQJ^^'^^^=KDR^^<^^^/LX^^6^^^/L^^=^^^%UDXQVWHLQ^^3^^^&RRSHUDWLYLW\^ in Highly Active Ethylene Dimerization by Dinuclear Nickel Complexes Bearing a Bifunctional PN Ligand. Organometallics 2021, 40, 184-193. doi: 10.1021/acs.organomet.0c00683 64. +DJKYHUGL^^0^^^7DGMDURGL^^$^^^%DKUL^/DOHK^^1^^^1HNRRPDQHVK^+DJKLJKL^^0^^^ 6\QWKHVLV^DQG^FKDUDFWHUL]DWLRQ^RI^1L^,,^^FRPSOH[HV^EHDULQJ^RI^^^^^H–EHQ]LPLGD]RO^^^\O^^ phenol derivatives as highly active catalysts for ethylene oligomerization. Appl. Organomet. Chem. 2018, 32. doi: 10.1002/aoc.4015 65. 0XNKHUMHH^^6^^^3DWHO^^%^^$^^^%KDGXUL^^6^^^6HOHFWLYH^(WK\OHQH^2OLJRPHUL]DWLRQ^ZLWK^ Nickel Oxime Complexes. Organometallics 2009, 28, 3074-3078. doi: 10.1021/om900080h 66. *XWVXO\DN^^'^^9^^^*RWW^^$^^/^^^3LHUV^^:^^(^^^3DUYH]^^0^^^'LPHUL]DWLRQ^RI^(WK\OHQH^E\^ Nickel Phosphino–Borate Complexes. Organometallics 2013, 32, 3363-3370. doi: 10.1021/om400288u 67. %RXOHQV^^3^^^3HOOLHU^^(^^^-HDQQHDX^^(^^^5HHN^^-^^1^^+^^^2OLYLHU-%RXUELJRX^^+^^^%UHXLO^^ P.-A. R., Self-Assembled Organometallic Nickel Complexes as Catalysts for Selective Dimerization of Ethylene into 1-Butene. Organometallics 2015, 34, 1139-1142. doi: 10.1021/acs.organomet.5b00055 68. The transition state observed for S=0 (singlet state) is 49.0 kcal molí1. Nonetheless, the diradical species (S=1) was also considered, as described in reference 21. However, this barrier was even higher in Gibbs free energy (83.4 kcal molí1). 69. 5tRV^^3^^^%RUJH^^-^^^)HUQiQGH]^'H^&yUGRYD^^)^^^6FLRUWLQR^^*^^^/OHGyV^^$^^^5RGUtJXH]^^ A., Ambiphilic boryl groups in a neutral Ni(II) complex: a new activation mode of H2. Chem. Sci. 2021, 12, 2540-2548. doi: 10.1039/d0sc06014c 70. +H^^7^^^7VYHWNRY^^1^^3^^^$QGLQR^^-^^*^^^*DR^^;^^^)XOOPHU^^%^^&^^^&DXOWRQ^^.^^*^^^ Mechanism of Heterolysis of H2 by an Unsaturated d8 Nickel Center: via Tetravalent Nickel? J. Am. Chem. Soc. 2010, 132, 910-911. doi: 10.1021/ja908674x 71. &UDLJ^^1^^&^^^*URQHU^^3^^^0F.HDQ^^'^^&^^^(TXLOLEULXP^6WUXFWXUHV^IRU^%XWDGLHQH^DQG^ (WK\OHQH^ௗ^&RPSHOOLQJ^(YLGHQFH^IRU^Ȇ-Electron Delocalization in Butadiene. J. Phys. Chem. A. 2006, 110, 7461-7469. doi: 10.1021/jp060695b
Thomas Horstemeyer Docket No.: 222117-2220 72. %URRNKDUW^^0^^^*UHHQ^^0^^/^^+^^^3DUNLQ^^*^^^$JRVWLF^LQWHUDFWLRQV^LQ^WUDQVLWLRQ^PHWDO^ compounds. Proc. Natl. Acad. Sci. U. S. A. 2007, 104, 6908-6914. doi: 10.1073/pnas.0610747104 73. )XOPHU^^*^^5^^^0LOOHU^^$^^-^^0^^^6KHUGHQ^^1^^+^^^*RWWOLHE^^+^^(^^^1XGHOPDQ^^$^^^6WROW]^^ %^^0^^^%HUFDZ^^-^^(^^^*ROGEHUJ^^.^^,^^^105^&KHPLFDO^6KLIWV^RI^7UDFH^,PSXULWLHV^^&RPPRQ^ Laboratory Solvents, Organics, and Gases in Deuterated Solvents Relevant to the Organometallic Chemist. Organometallics 2010, 29, 2176-2179. doi: 10.1021/om100106e It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. In an embodiment, the term “about” can include traditional rounding according to significant figures of the numerical value. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”. It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations, and are set forth only for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure.
, wherein Q is B, Al, Ga, In, or Tl, wherein each R is independently selected from an alkyl or aryl group, where X is a halogen, acetoxy group (OAc), or a polyatomic ion. 2. The composition of claim 1, wherein each R is independently selected from t-butyl group (tBu), phenyl group (Ph), or a cyclohexyl group (Cy). 3. The composition of claim 1, wherein each R is independently selected from a t-butyl group (tBu). 4. The composition of claim 3, wherein Q is B. 5. The composition of claim 1, wherein R is a phenyl group (Ph). 6. The composition of claim 5, wherein Q is B. 7. The composition of claim 1, wherein R is a cyclohexyl group (Cy). 8. The composition of claim 3, wherein Q is B. 9. The composition of claim 1, wherein R is an alkyl group. 10. The composition of claim 9, wherein Q is B. 11. The composition of claim 1, wherein R is an aryl group. 12. The composition of claim 11, wherein Q is B.
Thomas Horstemeyer Docket No.: 222117-2220 13. The composition of claim 1, wherein each R is independently selected from t-butyl group (tBu), phenyl group (Ph), or a cyclohexyl group (Cy), wherein Q is B, wherein X is a halogen. 14. The composition of claim 13, wherein X is Br. 15. The composition of claim 1, wherein each R is independently selected from t-butyl group (tBu), phenyl group (Ph), or a cyclohexyl group (Cy), wherein Q is B, wherein X is an acetoxy group (OAc). 16. The composition of claim 1, wherein polyatomic ion is BF4-, PF6-, or BAr4- (Ar = aryl group). 17. A method of making an alkene, comprising reacting an D-olefin and ethylene, with the composition of any one of claims 1 or 16. 18. The method of claim 16, wherein the D-olefin is a C3 to C20 D-olefin. 19. The method of claim 18, further comprising reacting ethylene, solvent, air, and N2 with the composition of any one of claims 1 or 16. 20. The method of claim 18, wherein the alkene is a C6 to C20 olefin. 21. The method of claim 18, wherein the alkene is butene, 1-hexene, or 1-octene. 22. The method of claim 21, wherein the butene comprises 1-butene, wherein about 70% or more of the butene formed is 1-butene. 23. The method of any one of claims 16-22, further comprising one or more of Ag+ or Na+ salts, alkylaluminum, or MAO. 24. The method of any one of claims 16-22, further comprising a Lewis acid.
Thomas Horstemeyer Docket No.: 222117-2220 25. The method of claim 24, wherein the Lewis acid is BF3, BBr3, or AlCl3. 26. A method of making an alkene, comprising reacting ethylene with the composition of any one of claims 1 or 15.