WO2020120935A1

WO2020120935A1 - Catalytic compounds for use in olefins polymerization

Info

Publication number: WO2020120935A1
Application number: PCT/GB2019/053444
Authority: WO
Inventors: Dermot O'hare; Jean-Charles BUFFET; Christopher Wright; Alexander Kilpatrick
Original assignee: Scg Chemicals Co., Ltd.
Priority date: 2018-12-10
Filing date: 2019-12-06
Publication date: 2020-06-18
Also published as: GB201820099D0

Abstract

Compounds suitable for use in the polymerisation of olefins, such as ethene, are described. Also described is a process for polymerising olefins using the described compounds.

Description

CATALYTIC COMPOUNDS FOR USE IN OLEFINS POLYMERIZATION

INTRODUCTION

[0001] The present invention relates to new catalytic compounds, more specifically, those that are suitable for use in the polymerisation of olefins, such as ethylene. Even more specifically, the present invention relates to ansa-metallocene compounds that are suitable for this use. The invention also relates to a process for the polymerisation of olefins, such as ethylene.

BACKGROUND OF THE INVENTION

[0002] It is well known that ethylene (and a-olefins in general) can be readily polymerised at low or medium pressures in the presence of certain transition metal catalysts. These catalysts are generally known as Zeigler-Natta type catalysts.

[0003] A particular group of these Ziegler-Natta type catalysts, which catalyse the polymerisation of ethylene (and a-olefins in general), comprise an aluminoxane activator and a metallocene transition metal catalyst. Metallocenes comprise a metal bound between two n⁵-cyclopentadienyl type ligands.

[0004] It is also well known that these r -cyclopentadienyl type ligands can be modified in a myriad of ways. One particular modification involves the introduction of a linking group between the two cyclopentadienyl rings to form ansa- metallocenes.

[0005] Numerous ansa- metallocenes of transition metals are known in the art. WO2011/051705 discloses ansa- metallocene catalysts based on two r -indenyl ligands linked via an ethylene group for use in the polymerisation of ethylene.

[0006] However, there remains a need for improved ansa- metallocene catalysts for use in olefin, in particular ethylene, polymerisation reactions. In particular, there remains a need for new metallocene catalysts with high polymerisation activities/efficiencies.

[0007] The present invention was devised with the foregoing in mind.

SUMMARY OF THE INVENTION

[0008] According to a first aspect of the present invention there is provided a compound having a structure according to formula I defined herein. [0009] According to a second aspect of the present invention there is provided a process for the polymerisation of at least one olefin, the process comprising the step of contacting a compound according to the first aspect with at least one olefin.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0010] The term "(m-nC)" or "(m-nC) group" used alone or as a prefix, refers to any group having m to n carbon atoms.

[0011] The term“alkyl” as used herein refers to straight or branched chain alkyl moieties, typically having 1 , 2, 3, 4, 5 or 6 carbon atoms. This term includes reference to groups such as methyl, ethyl, propyl (n-propyl or isopropyl), butyl (n-butyl, sec-butyl or tert-butyl), pentyl, hexyl and the like. In particular, an alkyl may have 1 , 2, 3 or 4 carbon atoms.

[0012] The term“alkenyl” as used herein refers to straight or branched chain alkenyl moieties, typically having 1 , 2, 3, 4, 5 or 6 carbon atoms. The term includes reference to alkenyl moieties containing 1 , 2 or 3 carbon-carbon double bonds (C=C). This term includes reference to groups such as ethenyl (vinyl), propenyl (allyl), butenyl, pentenyl and hexenyl, as well as both the cis and trans isomers thereof.

[0013] The term“alkynyl” as used herein refers to straight or branched chain alkynyl moieties, typically having 1 , 2, 3, 4, 5 or 6 carbon atoms. The term includes reference to alkynyl moieties containing 1 , 2 or 3 carbon-carbon triple bonds (CºC). This term includes reference to groups such as ethynyl, propynyl, butynyl, pentynyl and hexynyl.

[0014] The term“alkoxy” as used herein refers to -O-alkyl, wherein alkyl is straight or branched chain and comprises 1 , 2, 3, 4, 5 or 6 carbon atoms. In one class of embodiments, alkoxy has 1 , 2, 3 or 4 carbon atoms. This term includes reference to groups such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, tert-butoxy, pentoxy, hexoxy and the like.

[0015] The term "aryl" or“aromatic” as used herein means an aromatic ring system comprising 6, 7, 8, 9 or 10 ring carbon atoms. Aryl is often phenyl but may be a polycyclic ring system, having two or more rings, at least one of which is aromatic. This term includes reference to groups such as phenyl, naphthyl and the like. A particularly suitable aryl group is phenyl.

[0016] The term “aryl(m-nC)alkyl” refers to group -(CH2)_m-n-aryl, wherein aryl has any of definitions outlined above. A particular aryl(m-nC)alkyl group is benzyl.

[0017] The term“aryloxy” as used herein refers to -O-aryl, wherein aryl has any of the definitions discussed herein. [0018] The term“heteroaryl” or“heteroaromatic” means an aromatic mono-, bi-, or polycyclic ring incorporating one or more (for example 1-4, particularly 1 , 2 or 3) heteroatoms selected from nitrogen, oxygen or sulfur. Examples of heteroaryl groups are monocyclic and bicyclic groups containing from five to twelve ring members, and more usually from five to ten ring members. The heteroaryl group can be, for example, a 5- or 6-membered monocyclic ring or a 9- or 10- membered bicyclic ring, for example a bicyclic structure formed from fused five and six membered rings or two fused six membered rings. Each ring may contain up to about four heteroatoms typically selected from nitrogen, sulfur and oxygen. Typically the heteroaryl ring will contain up to 3 heteroatoms, more usually up to 2, for example a single heteroatom.

[0019] The term“heteroaryl(m-nC)alkyl” refers to group -(CFhV_n-heteroaryl, wherein heteroaryl has any of definitions outlined above.

[0020] The term“heteroaryloxy” as used herein refers to -O-heteroaryl, wherein heteroaryl has any of the definitions discussed herein.

[0021] The term "halogen" or“halo” as used herein refers to F, Cl, Br or I. In particular, halogen may Cl.

[0022] The term“substituted” as used herein in reference to a moiety means that one or more, especially up to 5, more especially 1 , 2 or 3, of the hydrogen atoms in said moiety are replaced independently of each other by the corresponding number of the described substituents. The term“optionally substituted” as used herein means substituted or unsubstituted.

[0023] It will, of course, be understood that substituents are only at positions where they are chemically possible, the person skilled in the art being able to decide (either experimentally or theoretically) without inappropriate effort whether a particular substitution is possible.

Compounds of the invention

[0024] According to a first aspect of the present invention there is provided a compound having a structure according to formula I shown below: wherein

R¹ is selected from the group consisting of (1-4C)alkyl, (2-4C)alkenyl, (1- 4C)alkoxy, aryloxy, aryl, aryl(1-2C)alkyl, heteroaryloxy, heteroaryl and heteroaryl(1- 2C)alkyl, wherein said (1-4C)alkyl, (2-4C)alkenyl, (1-4C)alkoxy, aryloxy, aryl, aryl(1- 2C)alkyl, heteroaryloxy, heteroaryl and heteroaryl(1-2C)alkyl are optionally substituted with one or more groups selected from the group consisting of halo, amino, hydroxy, (1- 4C)alkyl, (2-4C)alkenyl and (1-4C)alkoxy;

X is selected from zirconium or hafnium; and

each Y is independently selected from the group consisting of halo, (1-4C)alkyl, (1-4C)alkoxy and aryloxy, wherein said (1-4C)alkyl, (1-4C)alkoxy and aryloxy are optionally substituted with one or more groups selected from the group consisting of halo, amino, hydroxy and (1-4C)alkyl.

[0025] The compounds of formula I are effective initiators/catalysts in the polymerisation of olefins (e.g. a-olefins), such as ethene. The compounds of formula I are particularly effective initiators/catalysts in the homopolymerisation of ethene to produce a polyethylene homopolymer.

[0026] It will be understood by one of ordinary skill in the art that boron tends to form electron deficient configurations in which a trivalent boron atom has an incomplete outer shell of electrons. As a consequence, trivalent boron atoms typically have an affinity for an additional 2 electrons (e.g. an atom having a lone pair). It will therefore be understood that the present invention encompasses compounds of formula I wherein the boron atom is optionally coordinated to a lone pair-donating species. A particular example of such a lone pair-donating species is a solvent (e.g. an oxygen-containing solvent) in which the compound may have been synthesised, such as diethyl ether or tetrahydrofuran.

[0027] The compounds of the invention may be present in one or more isomeric forms. In particular, the compounds of the invention may be present as meso or rac isomers, and the invention includes both such isomeric forms. A person skilled in the art will appreciate that a mixture of isomers of the compound of the invention may be used for catalysis applications, or the isomers may be separated and used individually (using techniques well known in the art, such as, for example, fractional crystallisation).

[0028] It will be appreciated that the structural formula I presented above is intended to show the substituent groups in a clear manner. More representative illustrations of the spatial arrangement of the groups are shown below:

[0029] In an embodiment, R¹ is selected from the group consisting of (1-4C)alkyl, (1-4C)alkoxy, aryloxy, aryl, aryl(1-2C)alkyl, heteroaryl and heteroaryl(1-2C)alkyl, wherein said (1-4C)alkyl, (1- 4C)alkoxy, aryloxy, aryl, aryl(1-2C)alkyl, heteroaryl and heteroaryl(1-2C)alkyl are optionally substituted with one or more groups selected from the group consisting of halo, amino, hydroxy, (1-4C)alkyl and (1-4C)alkoxy.

[0030] Suitably, R¹ is selected from the group consisting of aryloxy, aryl, aryl(1-2C)alkyl, heteroaryl and heteroaryl(1-2C)alkyl, wherein said aryloxy, aryl, aryl(1-2C)alkyl, heteroaryl and heteroaryl(1-2C)alkyl are optionally substituted with one or more groups selected from the group consisting of halo, (1-4C)alkyl and (1-4C)alkoxy.

[0031] More suitably, R¹ is selected from the group consisting of phenoxy, phenyl, benzyl, 6- membered heteroaryl and 6-membered heteroaryl(1-2C)alkyl, wherein said phenoxy, phenyl, benzyl, 6-membered heteroaryl and 6-membered heteroaryl(1-2C)alkyl are optionally substituted with one or more groups selected from the group consisting of (1-4C)alkyl and (1-4C)alkoxy.

[0032] Even more suitably, R¹ is selected from the group consisting of phenoxy and phenyl, wherein said phenoxy and phenyl are optionally substituted with one or more groups selected from the group consisting of (1-4C)alkyl and (1-4C)alkoxy.

[0033] Yet more suitably, R¹ is phenyl optionally substituted with one or more (e.g. 1 , 2 or 3) groups selected from the group consisting of (1-4C)alkyl.

[0034] Most suitably, R¹ is phenyl. [0035] In an embodiment, X is Hf.

[0036] Most suitably, X is Zr.

[0037] The Y groups may be identical or different. Suitably, both Y groups are identical.

[0038] In an embodiment, each Y is independently selected from the group consisting of halo, (1-4C)alkyl, (1-4C)alkoxy and phenoxy, wherein said (1-4C)alkyl, (1-4C)alkoxy and phenoxy are optionally substituted with one or more groups selected from the group consisting of halo and (1- 4C) alkyl.

[0039] Suitably, each Y is independently selected from the group consisting of halo and (1- 4C)alkyl, wherein said (1-4C)alkyl is optionally substituted with one or more groups selected from the group consisting of halo and (1-2C)alkyl.

[0040] More suitably, each Y is independently selected from the group consisting of halo and (1- 2C)alkyl.

[0041] Even more suitably, each Y is independently selected from the group consisting of Cl and methyl.

[0042] Most suitably, both Y groups are Cl.

[0043] In an embodiment, the compound having a structure according to formula I has a structure according to formula la shown below:

wherein

each Y independently has any of those definitions appearing hereinbefore;

X has any of those definitions appearing hereinbefore;

Ph denotes phenyl; and

Q is selected from the group consisting of absent (in which case B is bonded directly to Ph), O and (CH2)_n, wherein n is 1 or 2. [0044] In an embodiment, the compound has a structure according to formula la, wherein Q is absent.

[0045] In an embodiment, the compound has a structure according to formula la, wherein Q is - (CH₂)-.

[0046] In an embodiment, the compound has a structure according to formula la, wherein Q is O.

[0047] In an embodiment, the compound having a structure according to formula I has a structure according to formula lb shown below:

wherein

each Y independently has any of those definitions appearing hereinbefore;

Ph denotes phenyl; and

Q is selected from the group consisting of absent (in which case B is bonded directly to Ph), O and (CH2)_n, wherein n is 1 or 2.

[0048] In an embodiment, the compound has a structure according to formula lb, wherein Q is absent.

[0049] In an embodiment, the compound has a structure according to formula lb, wherein Q is - (CH₂)-.

[0050] In an embodiment, the compound has a structure according to formula lb, wherein Q is O.

[0051] In an embodiment, the compound having a structure according to formula I has a structure according to formula lc shown below: wherein

X has any of those definitions appearing hereinbefore;

Ph denotes phenyl; and

[0052] In an embodiment, the compound has a structure according to formula lc, wherein Q is absent.

[0053] In an embodiment, the compound has a structure according to formula lc, wherein Q is - (CH₂)-.

[0054] In an embodiment, the compound has a structure according to formula lc, wherein Q is O.

[0055] In an embodiment, the compound has the following structure:

wherein Ph notes phenyl.

[0056] In an embodiment, the compound is associated with (e.g. immobilised on) a supporting substrate. Suitably, the supporting substrate is a solid. It will be appreciated that the compound may be immobilised on the supporting substrate by one or more covalent or ionic interactions, either directly, or via a suitable linking moiety. It will be appreciated that minor structural modifications resulting from the immobilisation of the compound of the supporting substrate (e.g. loss of one or both groups, Y) are nonetheless within the scope of the invention.

[0057] Suitably, the supporting substrate is selected from solid polymethylaluminoxane, silica, methylaluminoxane-activated silica, alumina, zeolite, layered double hydroxide and methylaluminoxane-activated layered double hydroxide.

[0058] More suitably, the supporting substrate is solid polymethylaluminoxane or methylaluminoxane-activated layered double hydroxide. The mole ratio of Al in the supporting substrate to metal X in the compound of formula I (i.e. [AI]/[X]) may be 50:1 to 400:1. Suitably, [AI]/[X] is 75:1 to 250:1.

[0059] In an embodiment, the supporting substrate is methylaluminoxane-activated layered double hydroxide (abbreviated herein as LDH/MAO). Methylaluminoxane-activated layered double hydroxide may be prepared by thermally-treating a layered double hydroxide (e.g. to a temperature of 150 - 450°C) and then contacting the thermally-treated layered double hydroxide with methylaluminoxane in a suitable solvent (e.g. toluene). In an embodiment, the methylaluminoxane-activated layered double hydroxide comprises 20 - 40 wt.% methylaluminoxane and 60 - 80 wt.% layered double hydroxide.

[0060] Suitably, the layered double hydroxide forming part of the methylaluminoxane-activated layered double hydroxide comprises a quantity of an organic solvent, the organic solvent having one or more hydrogen bond donor/acceptor moieties. Particular organic solvents include acetone, ethanol, 1-hexanol and ethyl acetate. Suitably, the organic solvent is 1-hexanol. Such layered double hydroxides may be prepared by known co-precipitation or hydrothermal techniques, whereby the water-wet (e.g. damp) as-prepared layered double hydroxides is contacted with (e.g. washed by or dispersed in) a quantity of the organic solvent prior to drying. Such layered double hydroxides may exhibit significantly higher surface areas than those that have been dried directly from the reaction liquor (i.e. water), thus making them particularly useful as catalytic support materials.

[0061] Suitably the methylaluminoxane-activated layered double hydroxide is a methylaluminoxane-activated Mg-AI-CC>3 layered double hydroxide or a methylaluminoxane- activated Mg-AI-NC>3 layered double hydroxide.

[0062] The mole ratio of Mg to Al in the layered double hydroxide forming part of the methylaluminoxane-activated layered double hydroxide is 2.0:1 to 4.0:1 . The mole ratio of Al in the LDH/MAO supporting substrate to metal X in the compound of formula I (i.e. [AI]/[X]) may be 50:1 to 150:1. [0063] In an embodiment, the supporting substrate is solid polymethylaluminoxane. The terms “solid MAO”,“sMAO” and“solid polymethylaluminoxane” are used synonymously herein to refer to a solid-phase material having the general formula -[(Me)AIO]_n-, wherein n is an integer from 4 to 50 (e.g. 10 to 50). Any suitable solid polymethylaluminoxane may be used.

[0064] There exist numerous substantial structural and behavioural differences between solid polymethylaluminoxane and other (non-solid) MAOs. Perhaps most notably, solid polymethylaluminoxane is distinguished from other MAOs as it is insoluble in hydrocarbon solvents and so acts as a heterogeneous support system. The solid polymethylaluminoxane useful in the compositions of the invention are insoluble in toluene and hexane.

[0065] In contrast to non-solid (hydrocarbon-soluble) MAOs, which are traditionally used as an activator species in slurry polymerisation or to modify the surface of a separate solid support material (e.g. S1O2), the solid polymethylaluminoxanes useful as part of the present invention are themselves suitable for use as solid-phase support materials, without the need for an additional activator. Hence, compounds of the invention supported on solid polymethylaluminoxane may be devoid of any other species that could be considered a solid support (e.g. inorganic material such as S1O2, AI2O3 and ZrC>₂). Moreover, given the dual function of the solid polymethylaluminoxane (as catalytic support and activator species), compounds of the invention supported on solid polymethylaluminoxane may not require the presence of an additional catalytic activator species (e.g. TIBA) when used in olefin polymerisation reactions.

[0066] In an embodiment, the solid polymethylaluminoxane is prepared by heating a solution containing MAO and a hydrocarbon solvent (e.g. toluene), so as to precipitate solid polymethylaluminoxane. The solution containing MAO and a hydrocarbon solvent may be prepared by reacting trimethyl aluminium and benzoic acid in a hydrocarbon solvent (e.g. toluene), and then heating the resulting mixture.

[0067] In an embodiment, the aluminium content of the solid polymethylaluminoxane falls within the range of 36-41 wt%.

[0068] The solid polymethylaluminoxane useful as part of the present invention is characterised by extremely low solubility in toluene and n-hexane. In an embodiment, the solubility in n-hexane at 25°C of the solid polymethylaluminoxane is 0-2 mol%. Suitably, the solubility in n-hexane at 25°C of the solid polymethylaluminoxane is 0-1 mol%. More suitably, the solubility in n-hexane at 25°C of the solid polymethylaluminoxane is 0-0.2 mol%. Alternatively or additionally, the solubility in toluene at 25°C of the solid polymethylaluminoxane is 0-2 mol%. Suitably, the solubility in toluene at 25°C of the solid polymethylaluminoxane is 0-1 mol%. More suitably, the solubility in toluene at 25°C of the solid polymethylaluminoxane is 0-0.5 mol%. The solubility in solvents can be measured by the method described in JP-B(KOKOKU)-H07 42301. [0069] In a particularly suitable embodiment, the solid polymethylaluminoxane is as described in WO2010/055652 or WO2013/146337, and is obtainable from Tosoh Finechem Corporation, Japan.

[0070] The mole ratio of Al in the solid polymethylaluminoxane supporting substrate to metal X in the compound of formula I (i.e. [AI]/[X]) may be 150:1 to 250:1.

Synthesis of compounds

[0071] The compounds of the invention may be formed by any suitable process known in the art. Particular examples of processes for the preparation of compounds of the invention are set out in the accompanying examples.

[0072] Generally, the process of preparing a compound of the invention as defined herein comprises:

(i) reacting a compound of formula A:

A

(wherein Ri is as defined hereinbefore and M is Li, Na or K)

with a compound of the formula B:

X(Y’)4

B

(wherein X is as defined hereinbefore and Y’ is halo (particularly chloro or bromo)) in the presence of a suitable solvent to form a compound of formula G: and optionally thereafter:

(ii) reacting the compound of formula G above with MY” (wherein M is as defined above and Y” is a group Y as defined herein other than halo), in the presence of a suitable solvent to form the compound of the formula I” shown below

[0073] Suitably, M is Li in step (i) of the process defined above.

[0074] The compound of formula B may be provided as a solvate, such as X(Y’)4.THF_P, where p is an integer (e.g. 2).

[0075] Any suitable solvent may be used for step (i) of the process defined above. A particularly suitable solvent is toluene, benzene or THF.

[0076] If a compound of formula I in which Y is other than halo is required, then the compound of formula G above may be further reacted in the manner defined in step (ii) to provide a compound of formula I”.

[0077] Any suitable solvent may be used for step (ii) of the process defined above. A suitable solvent may be, for example, diethyl ether, toluene, THF, dichloromethane, chloroform, hexane DMF, benzene etc. A person of skill in the art will be able to select suitable reaction conditions (e.g. temperature, pressures, reaction times, agitation etc.) for such a synthesis.

[0078] Compounds of formula A may generally be prepared by:

(i) reacting, in a suitable solvent (such as diethyl ether), two equivalents of a compound having formula C shown below

(wherein M is Li, Na or K) with one equivalent of a compound having formula D shown below:

R 1

LG /\ LG

D

(wherein R¹ has any of those definitions appearing hereinbefore; and each LG is independently a leaving group, e.g. Cl); and

(ii) reacting, in a suitable solvent (such as diethyl ether), the product of step (i) above with a basic organometallic compound (such as n-BuLi).

[0079] Compounds of formula D can be readily synthesised by techniques well known in the art.

[0080] A person of skill in the art will be able to select suitable reaction conditions (e.g. temperature, pressures, reaction times, agitation etc.) for such a synthesis.

Polymerisation of olefins

[0081] According to a second aspect of the present invention there is provided a process for the polymerisation of one or more olefins, the process comprising the step of contacting a compound according to the first aspect with at least one olefin. [0082] The compounds of formula I are effective initiators/catalysts in the polymerisation of olefins (e.g. a-olefins), such as ethene. The compounds of formula I are particularly effective initiators/catalysts in the homopolymerisation of ethene to produce a polyethylene homopolymer.

[0083] In an embodiment, the at least one olefin is at least one (2-10C)alkene. Suitably the at least one olefin is at least one a-olefin.

[0084] In an embodiment, the at least one olefin is ethene. The process may therefore be a homopolymerisation process for the preparation of a polyethylene homopolymer.

[0085] In an embodiment, the at least one olefin is ethene and optionally one or more other (3- 10C)alkenes (e.g. 1-hexene, styrene and/or methyl methacrylate). When the optional one or more other (3-10C)alkenes are present, the process may be a copolymerisation process for the preparation of a polyethylene-based copolymer.

[0086] In an embodiment, the at least one olefin is a mixture of 90 - 99 wt% ethene and 1 - 10 wt% of one or more other (3-10C)alkenes (e.g. 1-hexene, styrene and/or methyl methacrylate). The process may therefore be a copolymerisation process for the preparation of a polyethylene- based copolymer.

[0087] The process may be conducted in the presence of an activator or co-catalyst. Suitably, the activator or co-catalyst is one or more organoaluminium compounds. More suitably, the one or more organoaluminium compounds are selected from methylaluminoxane, triisobutylaluminium and triethylaluminium.

[0088] The person of ordinary skill in the art will be able to select appropriate conditions (e.g. temperature, pressure etc) for conducting the polymerisation process.

EXAMPLES

[0089] One or more examples of the invention will now be described, for the purpose of illustration only, with reference to the accompanying figures, in which:

Fig. 1 shows the ¹H NMR spectrum of (^PhBBI^*)H2 in Obϋ_d.

Fig. 2 shows the solid state structure of (^PhBBI*)H2. Thermal ellipsoids are drawn at 50% probability and hydrogen atoms have been omitted for clarity.

Fig. 3 shows the ¹H NMR spectrum of (^PhBBI^*)Li2.

Fig. 4 shows the ¹H NMR spectrum of rac-(^Ph BBI^*)ZrCl2 in Obϋ_d. Fig. 5 shows the solid state structure of rac-(^Ph BBI*)ZrCl2 obtained by recrystallisation from Et2<D. Thermal ellipsoids are drawn at 50% probability and hydrogen atoms have been omitted for clarity.

Fig. 6 shows temperature dependence on polymerisation activity of rac-(^Ph BBI*)ZrCl2 compared to industrial catalysts when supported on Mg_2.73AI-CC>₃-1-hexanol/MAO, [AI]o:[Zr]o=100: 1 ; TIBA cocatalyst (150 mg); 2 bar ethylene; 10 mg catalyst; 50 ml_ hexane, 30 minutes.

Fig. 7 shows the temperature dependence on polymerisation activity of rac-(^Ph BBI*)ZrCl2 supported on sMAO or on Mg_2.73AI-CC>₃-1-hexanol/MAO, [AI]o:[Zr]o= 200: 1 (sMAO), [AI]o:[Zr]o= 100: 1 (LDH/MAO); TIBA cocatalyst (150 mg); 2 bar ethylene; 10 mg catalyst; 50 ml_ hexane, 15 minutes (sMAO) or 30 minutes (LDH/MAO).

Fig. 8 shows the temperature dependence on the molecular weights of PE produced by supported rac-(^PhBBI^*)ZrCl2 systems. PDIs are given in parentheses. [AI]o:[Zr]o= 100: 1 (LDH/MAO), or 200: 1 (sMAO); TIBA cocatalyst (150 mg); 2 bar ethylene; 10 mg catalyst; 50 mL hexane, 30 minutes (LDH/MAO) or 15 minutes (sMAO).

Fig. 9 shows SEM images of polymer produced by (a) Mg_2.73AI-C0₃-1-hexanol/MAO/rac- (^PhBBI^*)ZrCI₂ and (b) sMAO/rac-(^PhBBI^*)ZrCI₂.

Example 1 - Preparation of ZrCl2

Synthesis of (^PhBBm?

[0090] Having regard to Scheme 1 below, to a solution of lnd^#Li (2 g, 9.70 mmol) in Et2<D (40 ml_) at 0 °C, was added dropwise a solution of PhBCh (0.6 ml_, 4.79 mmol) in Et2<D (20 ml_) at 0 °C. The suspension turned yellow and was allowed to warm to room temperature and stir for 18 h. The reaction was filtered and the residual solids were washed with Et2<D (3 x 20 ml_). The combined filtrates were dried in vacuo and the crude solids washed with pentane at 0 °C (3 x 20 ml_). The bulk yellow solid was redissolved in Et2<D and stored at -35 °C to afford yellow crystals suitable for X-ray diffraction analysis. A second crop of (^PhBBI*)H2 was obtained by storing the pentane washings at -35 °C. Compound (^PhBBI*)H2 was isolated in a total yield of 28% (640 mg, 1.32 mmol).

¹ H NMR (400 MHz, C₆D₆, 298 K): 6 8.10 (2H, m, o-PhH), 7.35 (3H, m, m, p- PhH), 4.18 (2H, s, IndH), 2.35 (6H, s, IndMe), 2.19 (6H, s, IndMe), 2.05 (6H, s, IndMe), 1.98 (6H, s, IndMe) and 1.67 (12H, s, IndMe). ¹³C{¹ H} NMR (125 MHz, C₆D₆, 298 K): <5 143.44 (Ind), 136.96 (Ind), 136.47 (Ind), 133.53 (o-Ph), 132.34 (Ind), 131.73 (p-Ph), 129.08 (Ind), 128.72 (m-Ph), 127.62 (Ind), 125.37 (Ind), 46.81 (IndH), 18.32 (IndMe), 16.51 (IndMe), 16.19 (IndMe), 16.16 (IndMe), 15.57 (IndMe) and 15.36 (IndMe). An additional Ind ¹³C resonance was expected, but was not observed, presumably obscured by the solvent resonance. Elemental analysis (%): Expected: C 88.87, H 8.91 ; found: C 88.76, H 8.60.

Scheme 1. Preparation of (^PhBBI*)H2from lnd^#Li

[0091] The ¹H NMR spectrum of (^PhBBI*)H2 in Obϋ_d (Figure 1) shows five singlets between 1.67 and 2.35 ppm (with one signal twice the intensity of the others) for the methyl groups. A resonance was observed for the allylic indenyl protons at 4.18 ppm, and two multiplets at 7.35 and 8.10 ppm correspond to the meta-lpara- and ortho-protons of the phenyl rings respectively.

[0092] Yellow crystals suitable for single crystal X-ray diffraction were grown from Et2<D at -35 °C in the triclinic space group P-1. The molecular structure is shown in Figure 2.

Synthesis of (^PhBBnLi?

[0093] Having regard to Scheme 2 shown below, to a solution of (^PhBBI*)H2 (500 mg, 1.03 mmol) in Et2<D (20 ml_) at 0 °C was added "BuLi (1.6 ml_, 1.6 M in hexanes, 2.56 mmol) dropwise, and the reaction left to warm to room temperature and stir for 2 h. A colour change from yellow to red was observed. The solvent was removed in vacuo and the residues were washed with pentane at 0 °C (2 x 20 ml_), to afford an orange powder in 68% yield (350 mg, 0.70 mmol).

¹H NMR (400 MHz, C₆D₅N, 298 K): 68.18 (2H, m, o-PhH), 7.14 (3H, m, m, p- PhH), 3.05 (6H, s, IndMe), 2.98 (6H, s, IndMe), 2.70 (6H, s, IndMe), 2.58 (6H, s, IndMe), 1.41 (6H, s, IndMe) and 1.27 (6H, s, IndMe). ⁷Li NMR (156 MHz, C₆D₅N, 298 K): 6 -0.74. Scheme 2. Preparation of (^PhBBI^*)Li₂from (^PhBBI^*)H₂

[0094] The ¹ H NMR spectrum in C₅D₅N of (^PhBBI*)Li₂ (Figure 3) showed 6 singlets between 1.27 and 3.05 ppm corresponding to the indenyl methyl groups, a multiplet at 7.14 ppm assigned to the meta- and para- phenyl protons, and a multiplet at 8.18 ppm assigned to the ortho- phenyl protons. The chemical shift for the indenyl methyl and phenyl protons have not significantly changed from (^PhBBI*)H₂, however the resonance at 4.18 ppm for the allylic indenyl proton is no longer observed in (^PhBBI*)Li₂, indicating total deprotonation by "BuLi.

Synthesis of (^PhBBnZrCI?

[0095] Having regard to Scheme 3 below, ZrCU (164 mg, 0.70 mmol) was added to (^PhBBI*)Li₂ (350 mg, 0.70 mmol), followed by toluene (30 ml_) and Et₂<D (1 ml_). The reaction was allowed to stir for 18 h and a colour change from pale to dark red was observed. The reaction was filtered, and the filtrate was dried under vacuum, yielding a red solid. This solid was washed with pentane (3 x 20 ml_), then dissolved in a minimum volume of Et₂<D and stored at -35 °C to obtain red crystals of isomerically pure rac-(^Ph BBI*)ZrCl₂, which were suitable for X-ray diffraction analysis, in a crystalline yield of 4% (20 mg, 0.030 mmol).

[0096] When ZrCU (164 mg, 0.70 mmol) was added to (^PhBBI*)Li₂ (350 mg, 0.70 mmol), followed by benzene (30 ml_) and the reaction was allowed to stir for 18 h, a colour change from pale to dark red was again observed. The reaction was dried, and washed with hexane (3 x 60 ml_). The reaction mixture was filtered and stored at -35 °C to obtain red crystals. ¹ H NMR spectroscopy showed a 2:1 rac- to meso- ratio of isomers.

¹ H NMR (rac-(^PhBBI*)ZrCI₂) (400 MHz, C₆D₆, 298 K): 6 8.50 (2H, m, o-PhH), 7.38 (3H, m, m-, p- PhH), 2.53 (6H, s, IndMe), 2.50 (6H, s, IndMe), 2.20 (6H, s, IndMe), 2.03 (6H, s, IndMe), 1.91 (6H, s, IndMe) and 1.79 (6H, s, IndMe). ¹ H NMR (meso-(^PhBBI*)ZrCI₂) (400 MHz, C₆D₆, 298 K): <5 8.55 (2H, m, o-PhH), 7.35 (3H, m, m-, p- PhH), 2.53 (6H, s, IndMe), 2.46 (6H, s, IndMe), 2.29 (6H, s, IndMe), 2.00 (6H, s, IndMe) and 1.87 (6H, s, IndMe) and 1.65 (6H, s, IndMe). ¹³C{¹ H} NMR {rac- 2.3) (125 MHz, C₆D₆, 298 K): <5 139.25 (o-Ph), 135.50 (m-Ph), 133.34 (Ind), 133.28 (Ind), 130.55 (Ind), 130.53 (Ind), 129.16 (Ind), 128.76 (p-Ph), 126.95 (Ind), 125.78 (Ind), 23.43 (IndMe), 17.26 (IndMe), 16.62 (IndMe), 16.27 (IndMe), 15.78 (IndMe) and 15.37 (IndMe). An additional two Ind ¹³C resonances were expected, but were not observed, presumably obscured by the solvent resonance. ¹¹ B{¹ H} NMR (rac-(^Ph BBI^*)ZrCI₂) (160 MHz, C₆D₆, 298 K): <5 73.5. MS (El) (rac-(^PhBBI^*)ZrCl2): Predicted: m/z 643.1781. Observed: m/z 643.1756. Elemental analysis (%) (rac-(^PhBBI^*)ZrCI₂): Expected: C 66.87, H 6.39; found: C 66.85, H 6.47

Scheme 3. Preparation of (^PhBBI^*)ZrCl2 from (^PhBBI^*)Li2

[0097] The ¹ H NMR spectrum of rac-(^Ph BBI^*)ZrCl2 in Obϋ_d, (Figure 4) shows 6 singlets of equal intensity between 1.79 and 2.53 ppm corresponding to the six methyl groups. Two multiplets observed at 7.38 and 8.50 ppm were attributed to the meta /para- and o/fPo-phenyl protons respectively.

[0098] Recrystallisation from Et2<D at -35 °C afforded single crystals of rac-(^Ph BBI^*)ZrCl2 suitable for X-ray diffraction, in the monoclinic space group P2i/c. The molecular structure is shown in Figure 4. In this synthesis, isomerically pure crystals were obtained in a 4% crystalline yield. Synthesis of rac-(^Ph BBI^*)ZrCl2 from (^PhBBI^*)Li2 in the absence of Et2<D with recrystallisation from hexane afforded a mixture of rac- and meso- products in a 2: 1 ratio.

[0099] It was expected that the Et2<D would act as a donor group to the boron atom. However there was no evidence of any tetra coordinated boron atoms in (^PhBBI^*)ZrCl2, either in the crystal structure or in the ¹ H NMR spectrum.

Example 2 - Immobilisation of zirconocene complexes on solid supports

[00100] The synthesis of Mg_2.73AI-C0₃-1-hexanol/MAO LDH/MAO was adapted from a literature procedure.¹·² A metal precursor solution, A, was formed by dissolving Mg(N0₃)₂-6H₂0 (10 g, 39 mmol) and AI(Nq₃)₃·9H₂q (4.9 g, 13 mmol) in 50 ml_ H2O. A second solution, B, was made by dissolving Na2CC>3 (2.76 g, 26 mmol) in 50 mL H2O. Solution A was added dropwise to solution B over the course of one hour. pH 10 was maintained throughout this step by dropwise addition of 4 M NaOH when necessary. After ageing 18 h, a white precipitate had formed. This was washed with H2O until the pH was close to 7, at which point the wet cake solid was rinsed with 1-hexanol (250 mL) abbreviated herein as“1 H”, and redispersed in the same solvent (400 mL), until the solid was well dispersed. Following the dispersion step, the solid was filtered and rinsed again with 1-hexanol (250 mL), before drying in a vacuum oven overnight at room temperature. The resultant solids were thermally treated under vacuum for 6 h at various temperatures and stored under a nitrogen atmosphere in a glovebox. 40 wt% MAO (200 mg) was then added to the thermally treated LDH (500mg). Toluene (40 mL) was added and the suspension was heated to 80 °C, and swirled every 10 minutes for 2 h, until the supernatant solution was clear and colourless. The solvent was removed under reduced pressure and the residual white solid dried in vacuo.

[00101] Solid polymethylaluminoxane (sMAO) was obtained from Tosoh Finechem Corp., Japan (commercial grade TMA0212).

[00102] In a typical procedure, the activated support (LDH/MAO, 200 mg, 0.98 mmo i; or sMAO, 200 mg, 2.97 mmoUi), and the zirconocene complex (4.8 mg, 0.00984 mmolz_r; or 7.2 mg, 0.01485 mmolz_r) were first added to a flask. Toluene was then added and the reaction mixture was heated to 60 °C, and swirled every 10 minutes for 1 h until the supernatant solution was clear and colourless. The supernatant solution was removed by filtration and the solid supported catalyst dried in vacuo. A 100: 1 [AI]:[Zr] was used for LDH/MAO supported complexes, and a 200: 1 [AI]:[Zr] was used for sMAO supported complexes.

Example 3 - Heterogeneous ethylene polymerisation

[00103] Slurry phase ethylene polymerisation studies were carried out using 10 g catalyst precursor and 50 ml_ hexane in the presence of 150 mg TIBA 150 mg in a 150 ml_ high-pressure RotaFlo ampoule. Polymerisation reactions were carried out under 2 bar overpressure of ethylene gas at various temperatures for 15 or 30 minutes. Polymerisations were stopped by removing the ampoules from the oil bath and degassing in vacuo. The PE produced were isolated and washed with pentane (50 ml_). Each polymerisation study was conducted at least twice to determine a mean activity (quoted in units of kgp_E molz_r ¹ IT¹ bar¹) and ensure reproducibility of the results.

[00104] Figure 6 shows a comparison of the ethylene polymerisation activity of rac-(^PhBBI^*)ZrCl2 and several catalysts favoured by industry supported on Mg_2.73AI-CC>₃-1-hexanol/MAO. At 80 °C, rac-(^PhBBI*)ZrCI₂ outperforms all the industrial catalysts tested, with a peak activity of 6641 kgp_E molz_r ^-1 h^-1 bar^-1 compared to 4438 kgp_E mob^-1 h^-1 bar^-1 for (Cp^Me4)₂ZrCI₂, the next most active complex. This may be due in part to the significant ring slip observed in the molecular structure of rac-(^PhBBI*)ZrCI₂, which opens up a vacant coordination site and reduces the electron count of the metal, thereby increasing the activity of the system.

[00105] When rac-(^PhBBI*)ZrCI₂ was supported on sMAO, it appeared more active than the Mg_2.73AI-CC>₃-1-hexanol/MAO based catalyst, with peak activities at 70 °C in both cases (Figure 7; 11049 and 6641 kgp_E mob^-1 h^-1 bar^-1 respectively). The sMAO supported catalyst was so active that before 30 minutes had elapsed the slurry was unable to keep stirring, and the PE was no longer free flowing. Therefore, it was decided to carry out 15 minutes experiments in order that the polymerisation was not stopped prematurely. When sMAO was used as a support for rac-(^PhBBI*)ZrCI₂ there was no observed temperature dependence, and the catalyst demonstrated equally high activity at 50°C as it did at 80°C. The peak activity (11049 kgp_E rnolz_r ^-1 h^-1 bar^-1) is notably higher than that previously reported for the analogous ethylene- bridged complex, sMAO/rac-(EBI^*)ZrCI₂ (5365 kgp_E rnolz_r ^-1 h^-1 bar^-1 ; 50 °C, 30 minutes, [AIMAO]O: [ZG]O=200: 1 ) and for the analogous dimethylsilylene-bridged complex, sMAO/rac-(SBI^*)ZrCI₂ (7760 kg_PE mol_Zr ^-1 lr¹ bar¹ ; 70 °C, 30 minutes, [AI]:[Zr]=300: 1).

Therefore, when supported on sMAO, rac-(^PhBBI*)ZrCI₂ is seen to be more active than rac-( EBI^*)ZrCI₂ and rac-(SBI^*)ZrCb

(EBI^*)ZrCI₂ (SBI^*)ZrCI₂

[00106] Furthermore, despite having been primarily envisaged for use in propene polymerisation reactions, rac-(^{Ph B} 2°BBI)ZrCI₂, in which the indenyl ligands are entirely unsubstituted, was tested by Reetz et al ³ for solution phase ethylene polymerisation, and only displayed activities of between 200 and 2600 kgp_E molz_r ^-1 h^-1. Typically, polymerisation reactions conducted in solution would be expected to proceed quicker than under heterogeneous slurry conditions due to the greater quantities of MAO that are often used in solution phase polymerisation reactions, as well as the fact that unsupported catalysts present a more readily accessible active site. Reetz’s attempts to improve the polymerisation activity of the rac-(^{Ph Et}2°BBI)ZrCl2 complex centred around forming boron adducts with donor molecules other than Et2<D.

[00107] The M_w of the PE produced by supported rac-(^Ph BBI*)ZrCl2 are shown in Figure 8. These systems produce lower molecular weight PE than the corresponding (Cp^Me4)₂ZrCl₂ systems, ranging between 150 and 250 kg mol ¹. Unusually, the M_w increases with temperature (Figure 8)

[00108] SEM images were taken of a selection of PE samples (Figure 9). The sMAO supported rac-(^PhBBI^*)ZrCl2 system produced more highly aggregated PE than Mg_2.73AI-CC>₃-1- hexanol/MAO supported rac-(^Ph BBI^*)ZrCl2.

[00109] While specific embodiments of the invention have been described herein for the purpose of reference and illustration, various modifications will be apparent to a person skilled in the art without departing from the scope of the invention as defined by the appended claims.

REFERENCES

1. C. Chen, M. Yang, Q. Wang, J.-C. Buffet and D. O’Hare, J. Mater. Chem. A, 2014, 2, 15102- 15110.

2. K. Ruengkajorn, V. Erastova, J.-C. Buffet, H. C. Greenwell and D. O’Hare, Chem. Commun., 2018, 54, 4394-4397.

3. M. T. Reetz, M. Willuhn, C. Psiorz, R. Goddard, Chem. Commun, 1999, 1105-1106

Claims

1. A compound having a structure according to formula I shown below:

wherein

X is selected from zirconium or hafnium; and

2. The compound of claim 1 , wherein R¹ is selected from the group consisting of (1- 4C)alkyl, (1-4C)alkoxy, aryloxy, aryl, aryl(1-2C)alkyl, heteroaryl and heteroaryl(1- 2C)alkyl, wherein said (1-4C)alkyl, (1-4C)alkoxy, aryloxy, aryl, aryl(1-2C)alkyl, heteroaryl and heteroaryl(1-2C)alkyl are optionally substituted with one or more groups selected from the group consisting of halo, amino, hydroxy, (1-4C)alkyl and (1- 4C)alkoxy.

3. The compound of claim 1 or 2, wherein R¹ is selected from the group consisting of aryloxy, aryl, aryl(1-2C)alkyl, heteroaryl and heteroaryl(1-2C)alkyl, wherein said aryloxy, aryl, aryl(1-2C)alkyl, heteroaryl and heteroaryl (1-2C) alkyl are optionally substituted with one or more groups selected from the group consisting of halo, (1-4C)alkyl and (1- 4C)alkoxy.

4. The compound of claim 1 , 2 or 3, wherein R¹ is selected from the group consisting of phenoxy, phenyl, benzyl, 6-membered heteroaryl and 6-membered heteroaryl(1- 2C)alkyl, wherein said phenoxy, phenyl, benzyl, 6-membered heteroaryl and 6- membered heteroaryl(1-2C)alkyl are optionally substituted with one or more groups selected from the group consisting of (1-4C)alkyl and (1-4C)alkoxy.

5. The compound of any preceding claim, wherein R¹ is selected from the group consisting of phenoxy and phenyl, wherein said phenoxy and phenyl are optionally substituted with one or more groups selected from the group consisting of (1-4C)alkyl and (1-4C)alkoxy.

6. The compound of any preceding claim, wherein R¹ is phenyl.

7. The compound of any preceding claim, wherein X is Zr.

8. The compound of any preceding claim, wherein each Y is independently selected from the group consisting of halo, (1-4C)alkyl, (1-4C)alkoxy and phenoxy, wherein said (1- 4C)alkyl, (1-4C)alkoxy and phenoxy are optionally substituted with one or more groups selected from the group consisting of halo and (1-4C)alkyl.

9. The compound of any preceding claim, wherein each Y is independently selected from the group consisting of halo and (1-4C)alkyl, wherein said (1-4C)alkyl is optionally substituted with one or more groups selected from the group consisting of halo and (1- 2C)alkyl.

10. The compound of any preceding claim,

wherein each Y is independently selected from the group consisting of halo and (1-

2C)alkyl;

or

wherein each Y is independently selected from the group consisting of Cl and methyl.

11. The compound of any preceding claim, wherein both Y are identical.

12. The compound of any preceding claim, wherein the compound has a structure

according to formula la shown below:

wherein

Ph denotes phenyl; and

Q is selected from the group consisting of absent, O and (CH2)_n, wherein n is 1 or 2.

13. The compound of any preceding claim, wherein the compound has a structure

according to formula lb shown below:

wherein

Ph denotes phenyl; and

14. The compound of any preceding claim, wherein the compound has a structure

according to formula lc shown below: wherein

Ph denotes phenyl; and

15. The compound of any preceding claim, wherein the compound has the following

structure:

wherein Ph notes phenyl.

16. The compound of any preceding claim, wherein the compound is immobilized on a supporting substrate,

optionally wherein the supporting substrate is a solid.

17. The compound of claim 16,

wherein the supporting substrate is selected from solid polymethylaluminoxane, silica, methylaluminoxane-activated silica, alumina, zeolite, layered double hydroxide and methylaluminoxane-activated layered double hydroxide, or

wherein the supporting substrate is solid polymethylaluminoxane or methylaluminoxane- activated layered double hydroxide.

18. A process for the polymerisation of at least one olefin, the process comprising the step of contacting the at least one olefin with a compound as claimed in any preceding claim.

19. The process of claim 18, wherein the at least one olefin is at least one (2-10C)alkene.

20. The process of claim 18 or 19, wherein the at least one olefin is at least one a-olefin.

21. The process of claim 18, 19 or 20, wherein the at least one olefin is ethene and

optionally one or more other (3-10C)alkenes (e.g. 1-hexene, styrene and/or methyl methacrylate).

22. The process of claim 18, 19 or 20, wherein the at least one olefin is ethene.

23. The process of any one of claims 18 to 22, wherein the process is conducted in the presence of an activator or co-catalyst.

24. The process of claim 23, wherein the activator or co-catalyst is one or more

organoaluminium compounds.

25. The process of claim 24, wherein the one or more organoaluminium compounds are selected from methylaluminoxane, triisobutylaluminium and triethylaluminium.