ES2478697A1 - Tris-imidazolium derivatives - Google Patents

Abstract

The invention relates to derivatives of highly symmetric tris-imidazolium salts of formula I, that have a central triphenylene nucleus, to a method for the production thereof from hexamine, and to the use of same as tris-NHC ligands for producing homo-hetero-trimetal complexes in tandem catalysis reactions and in the preparation of two-dimensional metal-organic frameworks (MOFs).

Description

Trisimidazolium derivatives

The present invention relates to new derivatives of trisimidazolium salts of formula I, their method of obtaining and their use in catalysis. Therefore, the invention could be framed in the field of catalytic chemistry.

STATE OF THE PREVIOUS TECHNIQUE

In recent years, interest in the design of macromolecules that are sensitive to external stimuli and that are linked by covalent bonds has increased considerably. The growing use of N-Heterocyclic Carbenes (NHC) has opened a new field for the manufacture of this type of macromolecules, in which it has been proposed to obtain conjugated polymers (CPs) and metallo- networks. organic (MOFs).

Obtaining these types of compounds requires the design of simple molecular starting systems (scaffolds) that allow obtaining the desired polymer in a simple and controlled way. However, despite the obvious applications that such materials can derive, currently only bisimidazolium salts capable of providing monodimensional linear polymers are known (Neilson, BM; Tennyson, AG; Bielawski, CWJ Phys. Org. Chem. 2012, 25, 531), whose electronic properties depend on the nature of the scaffold, the systems in which an effective delocalisation of the charge through the polymer is highly appreciated. Normally this delocalisation is achieved through the design of systems with a high delocalization π.

Thus, obtaining multitopic or multifunctional NHCs is essential for the development of new materials.

Bis-NHC systems have been described in the state of the art that can be used for the development of highly effective polymers, metallopolymers and catalysts in a wide variety of organic transformations (Boydston, AJ; Williams, KA; Bielawski, CWJ Am. Chem. Soc. 2005, 127, 12496).

The only rigid tris-NHC system described with D3h symmetry is that described by Bielawski, however, this system is electronically disconnected through a central ‘core’ formed by a triptylenic moiety.

Thus, it would be desirable to have heteromethalic molecules based on a dicarbeno-NHC bridge that provide catalytic efficiencies greater than those shown by the independent monometallic systems described in the prior art. That is, it would be desirable to have a method of obtaining bi-and three-dimensional polymers with a high capacity to transport optical and electronic stimuli.

DESCRIPTION OF THE INVENTION

The present invention describes the obtaining of tris-NHC systems with D3h symmetry, in which the three NHCs are communicated through delocalization π. The preparation of flat tris-NHC, with a high delocalization π, allows to obtain a great variety of two- and three-dimensional polymers with a high capacity to conduct optical and electronic stimuli. In parallel, the high delocalization provides the system with highly valued properties such as very intense UV / vis absorptions (typically π → π *), accessible bandahueco potentials, and photo- and electro-luminescence.

Among the applications of these systems, it is worth mentioning their usefulness in the preparation of metal-organic networks (MOFs), in the design of organic light-emitting diodes (OLEDs), as a component of the stationary phase in gas chromatography, in catalysis homogeneous, in the preparation of homo- and hetero-trimetallic complexes and in sensors for the detection of CO2.

Thus, one aspect of the present invention relates to a compound of formula I:

where:

R1 represents C1-C10alkyl or phenyl, where the phenyl is optionally substituted by one or more R2, C1-C4alkyl or - O-C1-C4alkyl; X represents R2, B (R3) 4, tetrakis [3,5-bis (trifluoromethyl) phenyl] borate or P (R3) 6;

5 R2 represents F, Cl, Br or I; and R3 represents F, Cl, Br or I. provided that all R1 groups of the compound of formula I are simultaneously equal to each other. Another aspect of the present invention relates to the process of obtaining a compound of formula I from

of a compound of formula IV in the presence of a trisakyl orthoformate, preferably HC (OEt) 3, and an acid of formula HX:

where:

R1 represents C1-C10alkyl or phenyl, where the phenyl is optionally substituted by one or more R 2, C1-C4alkyl or -O-C1-C4alkyl; Y

R2 represents F, Cl, Br or I.

Another aspect of the present invention relates to the use of a compound of formula I as a precursor of a tris-NHC ligand coordinated to three metals selected from Rh, Ir, Pd, Ru, Ni, Cu, Ag, Au or Pt, preferably Rh or Pd, to obtain a homo-tri-metallic complex, to prepare an ionic liquid, an organometallic polymer, a homogeneous catalyst, a metallo-organic network (MOF), an electro-optical sensor, a biosensor or a solar cell.

Throughout the present invention the "C1-C10alkyl" refers to an alkyl group of 1 to 10 carbons which can be linear or branched, preferably refers to a tert-C4-C10alkyl group. Examples include, among others, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, tert-butyl, tert-pentyl and isopropyl.

"C1-C4alkyl" refers to a group of 1 to 4 carbons that can be linear or branched and includes the methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl and tert-butyl groups.

"Tert-C4-C10alkyl" refers to a group of 1 to 4 branched carbons where the carbon atom that binds to the rest of the molecule is substituted by three alkyl groups, that is, it is a quaternary carbon atom. Examples include among others tert-butyl and tert-pentyl.

"-O-C1-C4alkyl" refers to a C1-C4alkyl group in which one of its hydrogens is substituted by an oxygen. Examples include methoxy, ethoxy, propyloxy, butoxy, tert-butoxy and sec-butoxy.

"Trisalkyl orthoformate" refers to an orthoester group of formic acid. Examples include among others HC (OEt) 3 and HC (OMe) 3.

The term "optionally substituted by one or more" means the possibility of a group being substituted by one or more, preferably by 1, 2, 3 or 4 substituents, more preferably by 1, 2 or 3 substituents and even more preferably by 1 or 2 substituents, provided that said group has sufficient available positions

35 likely to be replaced. If present, said substituents may be the same or different and may be located over any available position.

In another embodiment the invention relates to a compound of formula I as defined above, wherein:

R1 represents C1-C10alkyl; Y

C1-C10alkyl is selected from tert-C4-C10alkyl.

In another embodiment the invention relates to a compound of formula I as defined above,

where R 1 represents tert-pentyl or tert-butyl, preferably tert-butyl. In another embodiment the invention relates to a compound of formula I as defined above, where R1 represents ethyl.

In another embodiment the invention relates to a compound of formula I as defined above,

where R1 represents phenyl substituted by one or more CH3 groups. In another embodiment the invention relates to a compound of formula I as defined above, where:

R1 represents phenyl, where the phenyl is optionally substituted by one or more R2; and 10 R2 represents Cl.

In another embodiment the invention relates to a compound of formula I as defined above, where: R1 represents phenyl, where the phenyl is optionally substituted by one or more R2; Y R2 represents –OCH3.

In another embodiment the invention relates to a compound of formula I as defined above, wherein R 1 represents a group of formula II:

II In another embodiment the invention relates to a compound of formula I as defined above,

Where: X represents Cl, I, B (R2) 4, or P (R2) 6; and R2 represents F. In another embodiment the invention relates to a compound of formula I as defined above,

where:

X represents B (R3) 4, or P (R3) 6; and R3 represents F. In another embodiment the invention relates to a compound of formula I as defined above,

where: R1 represents tert-butyl;

X represents Cl, I, B (R3) 4, or P (R3) 6; and R3 represents F. In another embodiment the invention relates to a compound of formula I as defined above,

where: R1 represents tert-butyl; X represents B (R3) 4, or P (R3) 6; and R3 represents F.

In another embodiment the invention relates to a compound of formula I as defined above selected from:

3+

Me

3 (BF4-)

I

I

N

N

I

I

I

N NN Me Me

I I

I

I

I

N

I I

I ,

;

;

;

; Y

.

In some of the procedures detailed below it may be necessary or convenient to protect reactive or labile groups by conventional protecting groups. Both the nature of such protecting groups and the procedures for their introduction and removal are well known and are part of the state of the art (see for example Greene TW and Wuts PGM, "Protective Groups in Organic Synthesis", John Wiley & Sons, 4th edition, 2006). Whenever present

In some protective group, a subsequent deprotection stage will be necessary, which is carried out under the usual conditions in organic synthesis, such as those described in the reference mentioned above.

Unless otherwise indicated, in the methods described below the meanings of the different substituents are the meanings described above in relation to a compound of formula I.

In general, the compounds of formula I can be obtained by the method described in scheme 1:

Hexaamine IV consists of two steps. The first step, described in the literature (Yatabe, T .; Harbison, MA; Brand, JD; Wagner, M .; Mullen, K .; Samori, P .; Rabe, JP Journal of Materials Chemistry 2000, 10, 1519) It consists of the bromination of triphenylene. In a second step, hexaamine IV is obtained from the brominated compound by

a reaction of amination of Buchwald-Hartwig. The simplicity of the synthetic procedure makes it possible for compound I to be obtained in multi-gram scales. Cyclization of IV is performed using triethyl orthoformate (HC (OEt) 3) in acidic medium. Thus, IV is dissolved in HC (OEt) 3 and reacted with three equivalents of tetrafluoroboric acid. The reaction is heated, for example at 110 ° C for a time, for example for 16 h. A

5 times at room temperature, the tris-imidazolium I salt precipitates as a beige solid when diethyl ether is added. Compound I is obtained in a yield greater than 95%.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, the compounds of formula I have a three-pointed star shape (symmetry D3h), therefore possessing an axis of symmetry C3, which can be used for the preparation of

10 discrete molecules (trimetallic complexes) or two-dimensional metal-organic structures (known as MOFs) depending on the synthetic strategies employed.

On the one hand, the coordination of I as a tris-NHC ligand can result in trimetallic compounds (homo- and hetero-trimetallic) in which each metal is placed at the vertices of an equilateral triangle. Hetero-trimetallic compounds are of special interest since they can be applied in tandem catalytic reactions, in

15 that each metal fragment could promote a mechanistically different reaction.

On the other hand, as shown in scheme 2, this same ligand has a high potential as a starting material for building two-dimensional metal-organic networks or MOFs.

The procedure used for the activation of the compounds of formula I and their coordination with Rh (I), using the dimer [RhCl (cod)] 2 (cod = 1,5-cyclooctadiene) as a metal precursor is detailed in scheme 3 As mentioned above, coordination to other metals such as Pd, Ni, Ru, Au, Ir, Cu, Ag and Pt can be done using a similar procedure but with the corresponding metal precursors.

3+ (COD) Cl

3 (X-) Rh R1 N

R1 R1N N N

R1

one.

KHMDS, THF, 0 ° C

2.

[RhCl (COD)] 2

R1 R1 R 1 R1NN (COD)

Cl

RhN N RhR1 R1

I

R1 R1 (COD)

Cl V

Scheme 3

Thus, scheme 3 shows the procedure used for the coordination of the tris-NHC ligand derived from I to Rh (I). As the scheme illustrates, the synthesis consists of two stages. In the first step of the reaction, salt I is

5 suspended in dry THF and reacted with potassium bis (trimethylsilyl) amide (KHMDS) at 0 ° C for 10 minutes. Using this base, the free tris-NHC ligand is generated in solution. The free ligand is reacted in situ with the metal precursor, in this case [RhCl (cod)] 2. The resulting solution is stirred for 1.5 hours at room temperature. Purification is carried out by column chromatography.

As can be seen in scheme 3, the V complex is homo-trimetallic. Each of the three NHC units

10 is coordinated to a fragment of Rh (I). As a consequence of the ligand topology, the metal fragments are placed at the vertices of an equilateral triangle.

As mentioned above, the same synthetic procedure can be used for the coordination of I to other metal substrates (Ni, Ru, Au, Ir, Cu, Ag, Pt and Pd). The compounds obtained have significantly better catalytic properties than those presented by monometallic analogs, which implies

15 a great advantage at an economic level (less metal consumption for greater catalytic efficiency), as well as an obvious environmental benefit (less waste generation).

Likewise, the reaction of the trisazolium I salt with strong bases (ie: KHMDS) allows the generation of free tris-NHC, which can be polymerized to generate the two-dimensional homopolymer of formula VI shown in scheme 4. Load delocalization Two-dimensional of this polymer could be used in the manufacture of

20 photosensitizers, electro-optical filters and materials with advanced electrical properties.

Scheme 4

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other

5 technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples are provided by way of illustration, and are not intended to be limiting of the present invention.

10 EXAMPLES

Example 1. Obtaining I (R1 = tert-butyl)

3+

Me

3 (BF4-)

I

I

N

N

I

I

I

NN

I I I

I

MeN N

Me

I MeMe

In a round bottom flask, hexaamine IV (R = tert-butyl) (590 mg, 0.902 mmol) is dissolved in 40 mL of HC (OEt) 3. Then tetrafluoroboric acid (54% ethereal solution; 0.36 mL, 2,977 mmol) is added and allowed to stir at 110 ° C for 16 hours. Then, 100 mL of diethyl ether are added. The salt formed separates

5 by filtration. After precipitating with acetonitrile / diethyl ether, compound I is obtained pure as a beige solid. Yield: 820 mg, 95%.

1H NMR (300 MHz, DMSO-d6, 303 K): δ 9.19 (s, 6H, CHarom), 9.16 (s, 3H, NCHN), 2.04 (s, 54H, C (CH3) 3 ).

13C {1H} NMR (300 MHz, DMSO-d6, 303 K): 143.1 (NCHN), 131.8 (CHarom), 127.2 (Cq arom), 112.5 (Cq arom), 62.4 (C (CH3) 3), 29.0 (C (CH3) 3).

10 MS Electrospray (20V, m / z): 387.2 [M] 2+.

By a procedure analogous to that described above for obtaining the compound of example 1, the following compounds of formula I can be prepared with the corresponding starting compounds:

; ;

;

;

;

ice bath and KHMDS (0.5 M solution in toluene, 0.81 mL, 0.406 mmol) is added dropwise. It is left stirring for 10 minutes at 0 ° C. During this time, the solution acquires a dark red hue. In a second Schlenk, [RhCl (cod)] 2 (100 mg, 0.203 mmol) is introduced, and 5 mL of dry THF is added. The second solution is added on the first with the help of a cannula. The resulting mixture is stirred for 30 minutes at 0 ° C and 1.5

10 hours at 50 ° C. The solvent is removed under reduced pressure. The reaction crude is purified by column chromatography using silica gel as the stationary phase. By removing the solvent under reduced pressure, compound V is obtained as a crystalline yellow solid. Yield: 76.4 mg, 44%.

1H NMR (300 MHz, CDCl3, 303 K): δ 8.74 (s, 6H, CHarom), 5.11 (br s, 6H, CHcod), 3.08 (br s, 6H, CHcod), 2, 58 (s, 54H, C (CH3) 3), 2.42 (m, 12H, CH2 cod), 2.12 (m, 12H, CH2 cod).

15 13C {1H} NMR (300 MHz, CDCl3, 303 K): δ 200.7 (d, 1 JRh-C = 46.9 Hz, C-Rh), 135.4 (CHarom), 123.8 (Cq arom), 107.7 (Cq arom), 94.2 (CHcod), 67.8 (CHcod), 60.8 (C (CH3) 3), 32.4 (C (CH3) 3), 32.2 (CH2 cod ), 28.6 (CH2 cod).

MS electrospray (20V, m / z): 676.5 [M-2Cl] 2+.

Example 3: Obtaining compound VI.

5 10 minutes at 0 ° C. During this time, the solution acquires a dark red hue. In a second Schlenk, [PdCl (η3-allyl)] 2 (100 mg, 0.2734 mmol) is introduced and 5 mL of dry THF is added. The second solution is added on the first with the help of a cannula. The resulting mixture is stirred for 30 minutes at 0 ° C and 2 hours at room temperature. The solvent is removed under reduced pressure. The reaction crude is purified by column chromatography using silica gel as the stationary phase. By removing the solvent under pressure

Reduced, compound VI is obtained as a crystalline yellow solid. Yield: 80 mg, 36%.

1H NMR (300 MHz, CDCl3, 303 K): δ 8.86 (m, 6H, CHarom), 5.34 (m, 3H, CHalyl), 4.25 (m, 3H, CH2 allyl), 3.42 (m, 3H, CH2 allyl), 2.38 (s, 27H, C (CH3) 3), 2.20 (s, 27H, C (CH3) 3), 2.16 (m, 3H, CH2 allyl) , 1.59 (m, 3H, CH2 allyl).

13C {1H} NMR (300 MHz, CDCl3, 303 K): δ 193.8 (C-Pd), 135.3 (Cq arom), 124.4 (Cq arom), 112.8 (CHalyl), 108, 5 (CHarom), 69.0 (CH2 allyl), 60.20 (C (CH3) 3), 60.18 (C (CH3) 3), 51.6 (CH2 allyl), 31.8 (C (CH3 ) 3), 31.7 (C (CH3) 3).

15 MS Electrospray (20V, m / z): 1197 [M-Cl] +.

Example 4: Improvement in the catalytic activity of compound VI against the corresponding monometallic compound VII, in α-arylation of ketones.

Entry

Catalyst Cat load (% mmol) Time (h) Performance (%)

one

SAW 0,333  one 99

2

SAW 0,333  0.25 62

3

VII one one 75

Reaction conditions: T = 120 ° C, 0.5 mmol propiophenone, 0.55 mmol bromobenzene, 0.65 mmol NaOtBu, 2 mL of toluene. Yields obtained by GC using anisole as internal reference.

Ar-Br Input Product Time Cat Load Cat Yield%

(h) (% mol)

one

SAW 0,333 99

one

VII  one 65

one

SAW 0,333 99

1 VII 1 60

1 VI 0.333 99

1 VII 1 69

Reaction conditions: T = 120 ° C, 0.5 mmol propiophenone, 0.55 mmol bromoarene, 0.65 mmol NaOtBu, 2 mL of toluene. Yields obtained by GC using anisole as internal reference.

Claims (4)

1.- Compound of formula I: 5 where: R1 represents C1-C10alkyl or phenyl, where the phenyl is optionally substituted by one or more R2, C1-C4alkyl or - O-C1-C4alkyl; X represents R2, B (R3) 4, tetrakis [3,5-bis (trifluoromethyl) phenyl] borate or P (R3) 6; R2 represents F, Cl, Br or I; Y R3 represents F, Cl, Br or I. with the proviso that all R1 groups of the compound of formula I are simultaneously equal to each other. 2. The compound according to claim 1, wherein: R1 represents C1-C10alkyl; Y C1-C10alkyl is selected from tert-C4-C10alkyl. 3. The compound according to claim 2, wherein R1 represents tert-pentyl or tert-butyl. 4. The compound according to any of claims 1 to 3, wherein R1 represents tert-butyl. 5. The compound according to claim 1, wherein R1 represents ethyl. 6. The compound according to claim 1, wherein R1 represents phenyl substituted by one or more CH3 groups. 7. The compound according to claim 1, wherein: R1 represents phenyl, wherein the phenyl is optionally substituted by one or more R2: and R2 represents Cl. 8.- The compound according to claim 1, wherein: R1 represents phenyl, wherein the phenyl is optionally substituted by one or more R2; and R2 represents –OCH3. 9. The compound according to claim 1, wherein R1 represents a group of formula II: II  10. The compound according to any of claims 1 to 9, wherein: X represents Cl, I, B (R2) 4, or P (R2) 6; Y 5 R2 represents F. 11. The compound according to claim 10, wherein: X represents B (R3) 4, or P (R3) 6; Y R3 represents F. 12. The compound of formula I according to claim 1, wherein: R1 represents tert-butyl; X represents Cl, I, B (R3) 4, or P (R3) 6; and R3 represents F. 13. The compound of formula I according to claim 12 wherein: R1 represents tert-butyl; X represents B (R3) 4, or P (R3) 6; and R3 represents F. 14. The compound of formula I according to claim 1 selected from: 3+ Me 3 (BF4-) I Me n I I Me N N me I N I I Me N I I I , ; ; ; ; . 15.- Procedure for obtaining a compound of formula I from a compound formula IV in the presence of a trisalkyl orthoformate and an acid of formula HX: 5 where: R1 represents C1-C10alkyl or phenyl, where the phenyl is optionally substituted by one or more R2, C1-C4alkyl or - O-C1-C4alkyl; Y R2 represents F, Cl, Br or I. 16. The method according to claim 15, wherein the trisalkyl orthoformate is HC (OEt) 3. 17. 17. Use of a compound of formula I as a precursor of a tris-NHC ligand coordinated to three metals selected from Rh, Ir, Pd, Ru, Ni, Ag, Au or Pt to obtain a homo-tri-metallic complex. 18. The use of a compound of formula I according to claim 17, wherein the metal is selected from Rh or Pd. 19. The use according to any of claims 17 or 18, to obtain a homo-tri-metallic complex, to prepare an ionic liquid, an organometallic polymer, a homogeneous catalyst, a metallo-organic network (MOF), 15 an electro-optical sensor, a biosensor or a solar cell.