Abstract:
Novel unsymmetrical metallocene catalytic compounds of formula (I) are disclosed, as well as catalytic compositions comprising compounds of formula (I). Also disclosed are uses of such catalytic compounds and compositions in olefin polymerisation.

Description:
INTRODUCTION 
       [0001]    The present invention relates to catalysts. More specifically, the present invention relates to particular metallocene catalysts, and the use of such catalysts in polyolefin polymerization reactions. Even more specifically, the present invention relates to unsymmetrical metallocene catalysts, and the use of such catalysts in ethylene polymerization reactions. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is well known that ethylene (and a-olefins in general) can be readily polymerized 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 polymerization of ethylene (and a-olefins in general), comprise an aluminoxane activator and a metallocene transition metal catalyst. Metallocenes comprise a metal bound between two η 5 -cyclopentadienyl type ligands. Generally the η 5 -cyclopentadienyl type ligands are selected from η 5 -cyclopentadienyl, η 5 -indenyl and η 5 -fluorenyl. 
         [0004]    It is also well known that these η 5 -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. However, there remains a need for improved ansa-metallocene catalysts for use in polyolefin polymerization reactions. In particular, there remains a need for new metallocene catalysts with high polymerization activities/efficiencies. 
         [0006]    There is also a need for catalysts that can produce polyethylenes with particular characteristics. For example, catalysts capable of producing linear high density polyethylene (LHDPE) with a relatively narrow dispersion in polymer chain length are desirable. 
         [0007]    WO2011/051705 discloses ansa-metallocene catalysts based on two η 5 -indenyl ligands linked via an ethylene group. 
         [0008]    There remains a need for ansa-metallocene catalysts having improved polymerization activity. It is even further desirable that such catalysts can be easily synthesized. 
         [0009]    The present invention was devised with the foregoing in mind. 
       SUMMARY OF THE INVENTION 
       [0010]    According to a first aspect of the present invention there is provided a compound of formula (I) defined herein. 
         [0011]    According to a second aspect of the present invention, there is provided a use of a compound of formula (I) defined herein as a polymerisation procatalyst in the preparation of a polyethylene homopolymer or a copolymer comprising polyethylene. 
         [0012]    According to a third aspect of the present invention, there is provided a composition comprising a compound of formula (I) defined herein and a suitable activator as defined herein. 
         [0013]    According to a fourth aspect of the present invention, there is provided a use of a composition as defined herein as a polymerisation catalyst for the preparation of a polyethylene homopolymer or a copolymer comprising polyethylene 
         [0014]    According to a fifth aspect of the present invention, there is provided a process for forming a polyethylene homopolymer or a copolymer comprising polyethylene, the process comprising the step of reacting olefin monomers in the presence of (i) a compound of formula (I) defined herein, and (ii) a suitable activator as defined herein. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions 
       [0015]    The term “alkyl” as used herein includes reference to a 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 (including neopentyl), hexyl and the like. In particular, an alkyl may have 1, 2, 3 or 4 carbon atoms. 
         [0016]    The term “alkenyl” as used herein include reference to straight or branched chain alkenyl moieties, typically having 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. 
         [0017]    The term “alkynyl” as used herein include reference to straight or branched chain alkynyl moieties, typically having 2, 3, 4, 5 or 6 carbon atoms. The term includes reference to alkynyl moieties containing 1, 2 or 3 carbon-carbon triple bonds (C≡C). This term includes reference to groups such as ethynyl, propynyl, butynyl, pentynyl and hexynyl. 
         [0018]    The term “alkoxy” as used herein include reference 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. 
         [0019]    The term “aryl” as used herein includes reference to 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. 
         [0020]    The term “carbocyclyl” as used herein includes reference to an alicyclic moiety having 3, 4, 5, 6, 7 or 8 carbon atoms. The group may be a bridged or polycyclic ring system. More often cycloalkyl groups are monocyclic. This term includes reference to groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, norbornyl, bicyclo[2.2.2]octyl and the like. 
         [0021]    The term “heterocyclyl” as used herein includes reference to a saturated (e.g. heterocycloalkyl) or unsaturated (e.g. heteroaryl) heterocyclic ring moiety having from 3, 4, 5, 6, 7, 8, 9 or 10 ring atoms, at least one of which is selected from nitrogen, oxygen, phosphorus, silicon and sulphur. In particular, heterocyclyl includes a 3- to 10-membered ring or ring system and more particularly a 5- or 6-membered ring, which may be saturated or unsaturated. 
         [0022]    A heterocyclic moiety is, for example, selected from oxiranyl, azirinyl, 1,2-oxathiolanyl, imidazolyl, thienyl, furyl, tetrahydrofuryl, pyranyl, thiopyranyl, thianthrenyl, iso-benzofuranyl, benzofuranyl, chromenyl, 2H-pyrrolyl, pyrrolyl, pyrrolinyl, pyrrolidinyl, imidazolyl, imidazolidinyl, benzimidazolyl, pyrazolyl, pyrazinyl, pyrazolidinyl, thiazolyl, isothiazolyl, dithiazolyl, oxazolyl, isoxazolyl, pyridyl, pyrazinyl, pyrimidinyl, piperidyl, piperazinyl, pyridazinyl, morpholinyl, thiomorpholinyl, especially thiomorpholino, indolizinyl, isoindolyl, 3H-indolyl, indolyl, benzimidazolyl, cumaryl, indazolyl, triazolyl, tetrazolyl, purinyl, 4H-quinolizinyl, isoquinolyl, quinolyl, tetrahydroquinolyl, tetrahydroisoquinolyl, decahydroquinolyl, octahydroisoquinolyl, benzofuranyl, dibenzofuranyl, benzothiophenyl, dibenzothiophenyl, phthalazinyl, naphthyridinyl, quinoxalyl, quinazolinyl, quinazolinyl, cinnolinyl, pteridinyl, carbazolyl, β-carbolinyl, phenanthridinyl, acridinyl, perimidinyl, phenanthrolinyl, furazanyl, phenazinyl, phenothiazinyl, phenoxazinyl, chromenyl, isochromanyl, chromanyl and the like. 
         [0023]    The term “heteroaryl” as used herein includes reference to an aromatic heterocyclic ring system having 5, 6, 7, 8, 9 or 10 ring atoms, at least one of which is selected from nitrogen, oxygen and sulphur. The group may be a polycyclic ring system, having two or more rings, at least one of which is aromatic, but is more often monocyclic. This term includes reference to groups such as pyrimidinyl, furanyl, benzo[b]thiophenyl, thiophenyl, pyrrolyl, imidazolyl, pyrrolidinyl, pyridinyl, benzo[b]furanyl, pyrazinyl, purinyl, indolyl, benzimidazolyl, quinolinyl, phenothiazinyl, triazinyl, phthalazinyl, 2H-chromenyl, oxazolyl, isoxazolyl, thiazolyl, isoindolyl, indazolyl, purinyl, isoquinolinyl, quinazolinyl, pteridinyl and the like. 
         [0024]    The term “halogen” or “halo” as used herein includes reference to F, Cl, Br or I. In a particular, halogen may be F or Cl, of which Cl is more common. 
         [0025]    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. 
         [0026]    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. For example, amino or hydroxy groups with free hydrogen may be unstable if bound to carbon atoms with unsaturated (e.g. olefinic) bonds. Additionally, it will of course be understood that the substituents described herein may themselves be substituted by any substituent, subject to the aforementioned restriction to appropriate substitutions as recognised by the skilled person. 
       Catalytic Compounds 
       [0027]    As discussed hereinbefore, the present invention provides a compound of the formula (I) shown below: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein:
       R 1  and R 2  are each independently (1-2C)alkyl;   R 3  and R 4  are each independently hydrogen or (1-4C)alkyl, or R 3  and R 4  are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, halo, amino, nitro, cyano, (1-6C)alkylamino, [(1-6C)alkyl]2amino and —S(O) 2 (1-6C)alkyl;   R 5  and R 6  are each independently hydrogen or (1-4C)alkyl, or R 5  and R 6  are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, halo, amino, nitro, cyano, (1-6C)alkylamino, [(1-6C)alkyl]2amino and —S(O) 2 (1-6C)alkyl;   Q is a bridging group comprising 1, 2 or 3 bridging atoms selected from C, N, O, S, Ge, Sn, P, B, or Si, or a combination thereof, and is optionally substituted with one or more groups selected from hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl;   X is selected from zirconium, titanium or hafnium; and   each Y group is independently selected from halo, hydride, a phosphonated, sulfonated or borate anion, or a (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl or aryloxy group which is optionally substituted with one or more groups selected from (1-6C)alkyl, halo, nitro, amino, phenyl, —C(O)NR x R y , (1-6C)alkoxy, or Si[(1-4C)alkyl] 3 ;   wherein R x  and R y  are independently (1-4C)alkyl;
 
with the proviso that:
   i) when R 3  and R 4  are hydrogen or (1-4C)alkyl, R 5  and R 6  are not linked to form a fused 6-membered aromatic ring that is substituted with four methyl groups; and   ii) when R 5  and R 6  are hydrogen or (1-4C)alkyl, R 3  and R 4  are not linked to form a fused 6-membered aromatic ring that is substituted with four methyl groups.       
 
         [0037]    In an embodiment, the compound has a structure according to formula (I) wherein
       R 1  and R 2  are each independently (1-2C)alkyl;   R 3  and R 4  are each independently hydrogen or (1-4C)alkyl, or R 3  and R 4  are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, halo, amino, nitro, cyano, (1-6C)alkylamino, [(1-6C)alkyl]2amino and —S(O) 2 (1-6C)alkyl;   R 5  and R 6  are each independently hydrogen or (1-4C)alkyl, or R 5  and R 6  are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, halo, amino, nitro, cyano, (1-6C)alkylamino, [(1-6C)alkyl]2amino and —S(O) 2 (1-6C)alkyl;   Q is a bridging group comprising 1, 2 or 3 bridging atoms selected from C, N, O, S, Ge, Sn, P, B, or Si, or a combination thereof, and is optionally substituted with one or more groups selected from hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl;   X is selected from zirconium, titanium or hafnium; and   each Y group is independently selected from halo, hydride, a phosphonated, sulfonated or borate anion, or a (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl or aryloxy group which is optionally substituted with halo, nitro, amino, phenyl, —C(O)NR x R y , (1-6C)alkoxy, or Si[(1-4C)alkyl] 3 ;   wherein R x  and R y  are independently (1-4C)alkyl;
 
with the proviso that:
   i) when R 3  and R 4  are hydrogen or (1-4C)alkyl, R 5  and R 6  are not linked to form a fused 6-membered aromatic ring that is substituted with four methyl groups; and   ii) when R 5  and R 6  are hydrogen or (1-4C)alkyl, R 3  and R 4  are not linked to form a fused 6-membered aromatic ring that is substituted with four methyl groups.       
 
         [0047]    In another embodiment, the compound has a structure according to formula (I) wherein
       R 1  and R 2  are each independently (1-2C)alkyl;       
 
         [0049]    R 3  and R 4  are each independently hydrogen or (1-4C)alkyl, or R 3  and R 4  are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, halo, amino, nitro, cyano, (1-6C)alkylamino, [(1-6C)alkyl]2amino and —S(O)2(1-6C)alkyl;
       R 5  and R 6  are each independently hydrogen or (1-4C)alkyl, or R 5  and R 6  are linked such that, when taken in combination with the atoms to which they are attached, they form a 6-membered fused aromatic ring optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, halo, amino, nitro, cyano, (1-6C)alkylamino, [(1-6C)alkyl]2amino and —S(O) 2 (1-6C)alkyl;   Q is a bridging group comprising 1, 2 or 3 bridging atoms selected from C, N, O, S, Ge, Sn, P, B, or Si, or a combination thereof, and is optionally substituted with one or more groups selected from hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl;   X is selected from zirconium, titanium or hafnium; and   at least one Y group is an aryloxy group which is optionally substituted with one or more groups selected from (1-6C)alkyl, and the other Y group is independently selected from halo, hydride, a phosphonated, sulfonated or borate anion, or a (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl or aryloxy group which is optionally substituted with one or more groups selected from (1-6C)alkyl, halo, nitro, amino, phenyl, —C(O)NR x R y , (1-6C)alkoxy, or Si[(1-4C)alkyl] 3 ;   wherein R x  and R y  are independently (1-4C)alkyl;
 
with the proviso that:
   i) when R 3  and R 4  are hydrogen or (1-4C)alkyl, R 5  and R 6  are not linked to form a fused 6-membered aromatic ring that is substituted with four methyl groups; and   ii) when R 5  and R 6  are hydrogen or (1-4C)alkyl, R 3  and R 4  are not linked to form a fused 6-membered aromatic ring that is substituted with four methyl groups.       
 
         [0057]    Having regard to the proviso outlined above, it will be understood that the particular motifs not covered by the scope of the appended claims are as follows: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0058]    It will be appreciated that the structural formula (I) presented above is intended to show the substituent groups in a clear manner. A more representative illustration of the spatial arrangement of the groups is shown in the alternative representation below: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0059]    It will also be appreciated that when substituents R 3  and R 4  are not identical to substituents R 5  and R 6  respectively, the compounds of the present invention may be present as meso or rac isomers, and the present invention includes both such isomeric forms. A person skilled in the art will appreciate that a mixture of isomers of the compound of the present 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 crystallization). 
         [0060]    If the structure of a compound of formula (I) is such that rac and meso isomers do exist, the compound may be present in the rac form only, or in the meso form only. 
         [0061]    The unsymmetrical catalytic compounds of the invention exhibit superior catalytic performance when compared with current metallocene compounds used in the polymerisation of a-olefins. In particular, when compared with current metallocene compounds used in the polymerisation of a-olefins, the compounds of the invention exhibit increased catalytic activity. 
         [0062]    Suitably, when envisaged for use in the polymerisation of α-olefins, the compounds of the invention are immobilized on a suitable support as defined herein. The compounds of the invention may be immobilized directly on the support, or via a suitable linker. The compounds of the invention may be immobilized on the support by one or more ionic or covalent interactions. 
         [0063]    In an embodiment, R 3  and R 4  are each independently hydrogen or (1-4C)alkyl, or R 3  and R 4  are linked such that, when taken in combination with the atoms to which they are attached, they form a fused 6-membered aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino, nitro, cyano, (1-4C)alkylamino, [(1-4C)alkyl] 2 amino and —S(O) 2 (1-4C)alkyl; and 
         [0064]    R 5  and R 6  are each independently hydrogen or (1-4C)alkyl, or R 5  and R 6  are linked such that, when taken in combination with the atoms to which they are attached, they form a fused 6-membered aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino, nitro, cyano, (1-4C)alkylamino, [(1-4C)alkyl] 2 amino and —S(O) 2 (1-4C)alkyl. 
         [0065]    In another embodiment, R 3  and R 4  are each independently hydrogen or (1-4C)alkyl, or R 3  and R 4  are linked such that, when taken in combination with the atoms to which they are attached, they form a fused 6-membered aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro; and 
         [0066]    R 5  and R 6  are each independently hydrogen or (1-4C)alkyl, or R 5  and R 6  are linked such that, when taken in combination with the atoms to which they are attached, they form a fused 6-membered aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl, aryl, heteroaryl, carbocyclic and heterocyclic, wherein each aryl, heteroaryl, carbocyclic and heterocyclic group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro. 
         [0067]    In another embodiment, R 3  and R 4  are each independently hydrogen or (1-4C)alkyl, or R 3  and R 4  are linked such that, when taken in combination with the atoms to which they are attached, they form a fused 6-membered aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl, aryl and heteroaryl, wherein each aryl and heteroaryl group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro; and 
         [0068]    R 5  and R 6  are each independently hydrogen or (1-4C)alkyl, or R 5  and R 6  are linked such that, when taken in combination with the atoms to which they are attached, they form a fused 6-membered aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl, aryl and heteroaryl, wherein each aryl and heteroaryl group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro. 
         [0069]    In another embodiment, R 3  and R 4  are each independently hydrogen or (1-4C)alkyl, or R 3  and R 4  are linked such that, when taken in combination with the atoms to which they are attached, they form a fused 6-membered aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl and phenyl, wherein each phenyl group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro; and 
         [0070]    R 5  and R 6  are each independently hydrogen or (1-4C)alkyl, or R 5  and R 6  are linked such that, when taken in combination with the atoms to which they are attached, they form a fused 6-membered aromatic ring optionally substituted with one or more groups selected from (1-4C)alkyl and phenyl, wherein each phenyl group is optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro. 
         [0071]    In another embodiment:
       i) when R 3  and R 4  are hydrogen or (1-4C)alkyl, and R 5  and R 6  are linked to form a fused 6-membered aromatic ring, said ring is optionally substituted with one or two substituents as defined herein; or   ii) when R 5  and R 6  are hydrogen or (1-4C)alkyl, and R 3  and R 4  are linked to form a fused 6-membered aromatic ring, said ring is optionally substituted with one or two substituents as defined herein.       
 
         [0074]    In another embodiment, R 1  is methyl and R 2  is methyl or ethyl. 
         [0075]    In another embodiment, Q is a bridging group comprising 1, 2 or 3 bridging atoms selected from C, B, or Si, or a combination thereof, and is optionally substituted with one or more groups selected from hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl; 
         [0076]    In another embodiment, Q is a bridging group comprising 1, 2 or 3 bridging atoms selected from C, Si, or a combination thereof, and is optionally substituted with one or more groups selected from hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl. 
         [0077]    In another embodiment, Q is a bridging group selected from —[C(R a )(R b )-C(R c )(R d )]- and —[Si(R e )(R f )]-, wherein R a , R b , R c , R d , R e  and R f  are independently selected from hydrogen, hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl. Suitably, R a , R b , R c  and R d  are each hydrogen, and R e  and R f  are each independently (1-6C)alkyl, (2-6C)alkenyl or phenyl. More suitably, R a , R b , R c  and R d  are each hydrogen, and R e  and R f  are each independently (1 -4C)alkyl, (2-4C)alkenyl or phenyl. 
         [0078]    In an embodiment, Q is a bridging group having the formula —[Si(R e )(R f )]—, wherein R e  and R f  are each independently selected from methyl, ethyl, propyl, allyl or phenyl. Suitably, Q is a bridging group having the formula —[Si(R e )(R f )]—, wherein R e  and R f  are each independently selected from methyl, ethyl, propyl and allyl. More suitably, R e  and R f  are each methyl. 
         [0079]    In another embodiment, one Y group is a phenoxy group optionally substituted with 1, 2 or 3 groups independently selected from (1-3C)alkyl, and the other Y group is halo. 
         [0080]    In another embodiment, each Y group is independently selected from halo, hydride, a phosphonated, sulfonated or borate anion, or a (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy, aryl or aryloxy group which is optionally substituted with one or more groups selected from (1-6C)alkyl, halo, nitro, amino, phenyl, —C(O)NR x R y , (1-6C)alkoxy, or Si[(1-4C)alkyl] 3 , wherein R x  and R y  are independently (1 -4C)alkyl. 
         [0081]    In another embodiment, each Y is independently selected from halo or a (1-2C)alkyl or aryloxy group which is optionally substituted with one or more groups selected from (1-6C)alkyl, halo, phenyl, or Si[(1-4C)alkyl] 3 . Suitably, each Y is halo. 
         [0082]    In another embodiment, each Y is independently selected from halo or a (1-2C)alkyl group which is optionally substituted with halo, phenyl, or Si[(1-4C)alkyl] 3 . More suitably, each Y is Cl. 
         [0083]    In another embodiment, X is zirconium or hafnium. Suitably, X is zirconium. 
         [0084]    In another embodiment, the compound has any of formulae (II), (III) or (IV) shown below: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein:
       R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , Q, X and Y are each independently as defined in any of the paragraphs hereinbefore;   each R 7 , R 8  and R 9  is independently selected from any of the ring substituents defined in any of the paragraphs hereinbefore (e.g. any of the substituents present on 6-membered aromatic rings formed when either or both of (i) R 3  and R 4 , and (ii) R 5  and R 6 , are linked);   n, m and o are independently 0, 1, 2, 3 or 4.       
 
         [0088]    Suitably, n, m and o are independently 0, 1, or 2. More suitably, n, m and o are independently 0, 1 or 2. 
         [0089]    In another embodiment, in formulae (II), (III) or (IV), each R 7 , R 8  and R 9  is independently selected from hydrogen, (1-4C)alkyl and phenyl, said phenyl group being optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro. 
         [0090]    Suitably, in formulae (II), (III) or (IV), each R 7 , R 8  and R 9  is independently selected from hydrogen, methyl, n-butyl, tert-butyl and unsubstituted phenyl. 
         [0091]    In another embodiment, in formula (II), (III) or (IV), R 1  is methyl and R 2  is methyl or ethyl. 
         [0092]    In another embodiment, in formula (II), (III) or (IV), Q is a bridging group selected from —[C(R a )(R b )-C(R c )(R d )]— and —[Si(R e )(R f )]—, wherein R a , R b , R c , R d , R e  and R f  are independently selected from hydrogen, hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl. Suitably, Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from hydrogen, hydroxyl and (1-6C)alkyl. More suitably, Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from (1-6C)alkyl (e.g. methyl, ethyl, propyl or allyl). 
         [0093]    In a particular embodiment, the compound has any of formulae (II), (III) or (IV), wherein
       R 1  and R 2  are each independently (1-2C)alkyl;   R 3 , R 4 , R 5  and R 6  are each independently hydrogen or (1-4C)alkyl;   R 7 , R 5  and R 9  are each independently selected from hydrogen, (1-4C)alkyl and phenyl, said phenyl group being optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro;   n, m and o are each independently 1 or 2;   Q is a bridging group selected from —[C(R a )(R b )—C(R c )(R d )]— and —[Si(R e )(R f )]—, wherein R a , R b , R c , R d , R e  and R f  are independently selected from hydrogen, hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl;   each Y is independently selected from halo or a (1-2C)alkyl group which is optionally substituted with halo, phenyl, or Si[(1-4C)alkyl] 3 ; and   X is zirconium or hafnium.       
 
         [0101]    In another particular embodiment, the compound has any of formulae (II), (III) or (IV), wherein
       R 1  and R 2  are each independently (1-2C)alkyl;       
 
         [0103]    R 3 , R 4 , R 5  and R 6  are each independently hydrogen or (1-4C)alkyl;
       R 7 , R 5  and R 9  are each independently selected from hydrogen, (1-4C)alkyl and phenyl, said phenyl group being optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro;   n, m and o are each independently 1 or 2;   Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from hydrogen, hydroxyl and (1-6C)alkyl;   each Y is independently selected from halo, (1-2C)alkyl, or an aryloxy group which is optionally substituted with one or more substituents selected from (1-4C)alkyl, halo, phenyl, or Si[(1-4C)alkyl] 3 ; and   X is zirconium or hafnium.       
 
         [0109]    In another particular embodiment, the compound has any of formulae (II), (III) or (IV), wherein
       R 1  is methyl and R 2  is methyl or ethyl;       
 
         [0111]    R 3 , R 4 , R 5  and R 6  are each independently hydrogen or (1-4C)alkyl; 
         [0112]    R 7 , R 8  and R 9  are each independently selected from hydrogen, (1-4C)alkyl and phenyl, said phenyl group being optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro;
       n, m and o are each independently 1 or 2;   Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from hydrogen, hydroxyl and (1-6C)alkyl;   each Y is independently selected from halo, (1-2C)alkyl, or an aryloxy group which is optionally substituted with one or more substituents selected from (1-4C)alkyl, halo, phenyl, or Si[(1-4C)alkyl] 3 ; and   X is zirconium or hafnium.       
 
         [0117]    In another particular embodiment, the compound has any of formulae (II), (III) or (IV), wherein
       R 1  is methyl and R 2  is methyl or ethyl;   R 3 , R 4 , R 5  and R 6  are each independently hydrogen or (1-4C)alkyl;   R 7 , R 8  and R 9  are each independently selected from hydrogen, (1-4C)alkyl and phenyl, said phenyl group being optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro;   n, m and o are each independently 1 or 2;   Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from (1-6C)alkyl;   each Y is independently selected from halo, (1-2C)alkyl, or an aryloxy group which is optionally substituted with one or more substituents selected from (1-4C)alkyl, halo, phenyl, or Si[(1-4C)alkyl] 3 ; and   X is zirconium or hafnium.       
 
         [0125]    In another embodiment, the compound has any of formulae (V), (VI) or (VII) shown below: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein
       R 1 , R 2 , R 3 , R 5 , R 6 , Q, X and Y are each independently as defined in any of the paragraphs hereinbefore;   R 7 , R 8  and R 9  are each independently as defined in any of the paragraphs hereinbefore; and   R 4  is as defined in any of the paragraphs hereinbefore. Suitably, R 4  is hydrogen.       
 
         [0129]    Suitably, each R 7 , R 8  and R 9  in formulae (V), (VI) or (VII) is independently selected from hydrogen, (1-4C)alkyl and phenyl, said phenyl group being optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro. 
         [0130]    Suitably, each R 7 , R 8  and R 9  in formulae (V), (VI) or (VII) is independently selected from hydrogen, methyl, n-butyl, tert-butyl and unsubstituted phenyl. 
         [0131]    In another embodiment, in formula (V), (VI) or (VII), Q is a bridging group selected from —[C(R a )(R b )—C(R c )(R d )]— and —[Si(R e )(R f )]—, wherein R a , R b , R c , R d , R e  and R f  are independently selected from hydrogen, hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl. Suitably, Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from hydrogen, hydroxyl and (1-6C)alkyl. More suitably, Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from (1-6C)alkyl (e.g. methyl, ethyl, propyl or allyl). 
         [0132]    In another embodiment, in formula (V), (VI) or (VII), R 1  is methyl and R 2  is methyl or ethyl. 
         [0133]    In a particular embodiment, the compound has any of formulae (V), (VI) or (VII), wherein
       R 1  and R 2  are each independently (1-2C)alkyl;   R 3 , R 4 , R 5  and R 6  are each independently hydrogen or (1-4C)alkyl;   R 7 , R 8  and R 9  are each independently selected from hydrogen, (1-4C)alkyl and phenyl, said phenyl group being optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro;   Q is a bridging group selected from —[C(R a )(R b )—C(R c )(R d )]— and —[Si(R e )(R f )]—, wherein R a , R b , R c , R d , R e  and R f  are independently selected from hydrogen, hydroxyl, (1-6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (1-6C)alkoxy and aryl;   each Y is independently selected from halo or a (1-2C)alkyl group which is optionally substituted with halo, phenyl, or Si[(1-4C)alkyl] 3 ; and   X is zirconium or hafnium.       
 
         [0140]    In another particular embodiment, the compound has any of formulae (V), (VI) or (VII), wherein
       R 1  and R 2  are each independently (1-2C)alkyl;   R 3 , R 4 , R 5  and R 6  are each independently hydrogen or (1-4C)alkyl;   R 7 , R 5  and R 9  are each independently selected from hydrogen, methyl, n-butyl, tert-butyl and unsubstituted phenyl;   Q is a bridging group selected from —[C(R a )(R b )—C(R c )(R d )]— and —[Si(R e )(R f )]—, wherein R a , R b , R c  and R d  are each hydrogen, and R e  and R f  are each independently (1-6C)alkyl, (2-6C)alkenyl or phenyl;   each Y is independently selected from halo or a (1-2C)alkyl group which is optionally substituted with halo, phenyl, or Si[(1-4C)alkyl] 3 ; and   X is zirconium or hafnium.       
 
         [0147]    In another particular embodiment, the compound has any of formulae (V), (VI) or (VII), wherein
       R 1  and R 2  are each independently (1-2C)alkyl;   R 3 , R 4 , R 5  and R 6  are each independently hydrogen or (1-4C)alkyl;   R 7 , R 8  and R 9  are each independently selected from hydrogen, methyl, n-butyl, tert-butyl and unsubstituted phenyl;   Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from hydrogen, hydroxyl and (1-6C)alkyl;   each Y is independently selected from halo, (1-2C)alkyl, or an aryloxy group which is optionally substituted with one or more substituents selected from (1-4C)alkyl, halo, phenyl, or Si[(1-4C)alkyl] 3 ; and   X is zirconium or hafnium.       
 
         [0154]    In another particular embodiment, the compound has any of formulae (V), (VI) or (VII), wherein
       R 1  is methyl and R 2  is methyl or ethyl;   R 3 , R 4 , R 5  and R 6  are each independently hydrogen or (1-4C)alkyl;   R 7 , R 8  and R 9  are each independently selected from hydrogen, methyl, n-butyl, tert-butyl and unsubstituted phenyl;   Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from hydrogen, hydroxyl and (1-6C)alkyl;   each Y is independently selected from halo, (1-2C)alkyl, or an aryloxy group which is optionally substituted with one or more substituents selected from (1-4C)alkyl, halo, phenyl, or Si[(1-4C)alkyl] 3 ; and   X is zirconium or hafnium.       
 
         [0161]    In another particular embodiment, the compound has any of formulae (V), (VI) or (VII), wherein
       R 1  is methyl and R 2  is methyl or ethyl;   R 3 , R 4 , R 5  and R 6  are each independently hydrogen or (1-4C)alkyl;   R 7 , R 8  and R 9  are each independently selected from hydrogen, (1-4C)alkyl and phenyl, said phenyl group being optionally substituted with one or more groups selected from (1-4C)alkyl, (2-4C)alkenyl, (2-4C)alkynyl, (1-4C)alkoxy, halo, amino and nitro;   n, m and o are each independently 1 or 2;   Q is a bridging group —[Si(R e )(R f )]—, wherein R e  and R f  are independently selected from (1-6C)alkyl;   each Y is independently selected from halo, (1-2C)alkyl, or an aryloxy group which is optionally substituted with one or more substituents selected from (1-4C)alkyl, halo, phenyl, or Si[(1-4C)alkyl] 3 ; and   X is zirconium or hafnium.       
 
         [0169]    In another embodiment, the compound of formula I has any one of the following structures 
         [0000]    
       
                 
         
             
             
         
       
       
                 
         
             
             
         
       
     
         [0170]    In another embodiment, the compound has a structure according to formula VIII shown below: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein
       R 1  and R 2  are independently (1 -2C)alkyl; and   R e  and R f  are independently (1 -3C)alkyl.       
 
         [0173]    In another embodiment, the compound has the following structure: 
         [0000]    
       
                 
         
             
             
         
       
     
       Synthesis 
       [0174]    The compounds of the present invention may be synthesised by any suitable process known in the art. Particular examples of processes for the preparing compounds of the present invention are set out in the accompanying examples. 
         [0175]    Suitably, a compound of the present invention is prepared by:
       (i) reacting a compound of formula A:       
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    (wherein R 1 , R 2,  R 3 , Ra, R 5 , R 6  and Q are each as defined hereinbefore and M is Li, Na or K)
 
with a compound of the formula B:
 
         [0000]      X(Y′) 4    (B)
 
         [0000]    (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 (Ia): 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and optionally thereafter:
       (ii) reacting the compound of formula la 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 (Ib) shown below       
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0178]    Suitably, M is Li in step (i) of the process defined above. 
         [0179]    Suitably, the compound of formula B is provided as a solvate. In particular, the compound of formula B may be provided as X(Y′) 4 .THF p , where p is an integer (e.g. 2). 
         [0180]    Any suitable solvent may be used for step (i) of the process defined above. A particularly suitable solvent is toluene or THF. 
         [0181]    If a compound of formula (I) in which Y is other than halo is required, then the compound of formula (Ia) above may be further reacted in the manner defined in step (ii) to provide a compound of formula (Ib). 
         [0182]    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, dicloromethane, chloroform, hexane DMF, benzene etc. 
         [0183]    Compounds of formula A, in which Q is —[Si(R e )(R f )]—, may generally be prepared by:
       (i) Reacting a compound of formula D       
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    (wherein M is lithium, sodium, or potassium; and R 1  and R 2  are as defined hereinbefore) with one equivalent of a compound having formula E shown below: 
         [0000]      Si(Re)(R f )(Cl) 2    (E)
 
         [0000]    (wherein R e  and R f  are as defined hereinbefore)
 
to form the compound of the formula F shown below:
 
         [0000]    
       
                 
         
             
             
         
       
       
         
           
             (ii) Reacting the compound of formula F with a compound of formula G shown below: 
           
         
       
     
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    (wherein R 3 , R 4 , R 5  and R 6  are as defined hereinbefore, and M is lithium, sodium or potassium). 
         [0186]    Compounds of formulae D and G can be readily synthesized by techniques well known in the art. 
         [0187]    Any suitable solvent may be used for step (i) of the above process. A particularly suitable solvent is THF. 
         [0188]    Similarly, any suitable solvent may be used for step (ii) of the above process. A suitable solvent may be, for example, toluene, THF, DMF etc. 
         [0189]    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. 
         [0190]    Compounds of formula A, in which Q is —CH 2 —CH 2 —, may generally be prepared by:
       (i) Reacting a compound of formula D       
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    (wherein M is lithium, sodium, or potassium; and R 1  and R 2  are as defined hereinbefore) with an excess of BrCH 2 CH 2 Br to form a compound of the formula H shown below: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    (wherein R 1  and R 2  are as defined hereinbefore); and
       (ii) Reacting the compound of formula H with a compound of formula G shown below:       
 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    (wherein R 3 , R 4 , R 5  and R 6  are as defined hereinbefore, and M is lithium, sodium or potassium) 
         [0193]    Compounds of formulae D and G can be readily synthesized by techniques well known in the art. 
         [0194]    Any suitable solvent may be used for step (i) of the above process. A particularly suitable solvent is THF. 
         [0195]    Similarly, any suitable solvent may be used for step (ii) of the above process. A suitable solvent may be, for example, toluene, THF, DMF etc. 
         [0196]    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. 
       Applications 
       [0197]    As previously indicated, the compounds of the present invention are extremely effective as catalysts in polyethylene polymerization reactions. 
         [0198]    As discussed hereinbefore, the compounds of the invention exhibit superior catalytic performance when compared with current metallocene compounds used in the polymerisation of α-olefins. In particular, when compared with current metallocene compounds used in the polymerisation of α-olefins, the compounds of the invention exhibit significantly increased catalytic activity. 
         [0199]    Thus, as discussed hereinbefore, the present invention also provides the use of a compound of formula I as defined herein as a polymerization catalyst, in particular in the preparation of polyethylene. 
         [0200]    In one embodiment, the polyethylene is a homopolymer made from polymerized ethene monomers. 
         [0201]    In another embodiment, the polyethylene is a copolymer made from polymerized ethene monomers comprising 1-10 wt % of (4-8C) α-olefin (by total weight of the monomers). Suitably, the (4-8C) α-olefin is 1-butene, 1-hexene, 1-octene, or a mixture thereof. 
         [0202]    In another embodiment, the polyethylene is a polyethylene wax. Polyethylene wax will be understood by one of skill in the art as being low molecular weight polyethylene, typically having an average molecular weight of 1000-15,000 Da. Suitably, the polyethylene wax has an average molecular weight of 1000-6000 Da. 
         [0203]    As discussed hereinbefore, the present invention also provides a composition comprising a compound of formula (I) defined herein and at least one suitable activator. 
         [0204]    Suitable activators are well known in the art and include organo aluminium compounds (e.g. alkyl aluminium compounds). Particularly suitable activators include aluminoxanes (e.g. methylaluminoxane (MAO)), triisobutylaluminium (TIBA), diethylaluminium (DEAC) and triethylaluminium (TEA). 
         [0205]    In another embodiment, the compound of formula (I) may be immobilized on a suitable support. Suitably, the support is insoluble under the polymerisation conditions. Examples of suitable supports include silicas, layered-double hydroxides (LDH, e.g. AMO-LDH MgAl-CO 3 ), and any other inorganic support material. Supports such as silica and AMO-LDH may be subjected to a heat treatment prior to use. An exemplary heat treatment involves heating the support to 400-600° C. (for silicas) or 100-150° C. (for AMO-LDHs) in a nitrogen atmosphere. 
         [0206]    An exemplary layered double hydroxide is [Mg 1-x Al x (OH) 2 ] x+ (A n− ) x/n+ y(H 2 O).w(solvent), in which 0.1&lt;x&gt;0.9; A=anion eg. CO 3   2− , OH − , F − , Cl − , Br − , I − , SO 4   2− , NO 3   −  and PO 4   3− ; w is a number less than 1; y is 0 or a number greater than 0 which gives compounds optionally hydrated with a stoichiometric amount or a non-stoichiometric amount of water and/or an aqueous-miscible organic solvent (AMO-solvent), such as acetone. 
         [0207]    Suitably, the support is an activated support. The support may be activated by the presence of a suitable activator being covalently bound to the support. Suitably activators include organo aluminium compounds (e.g. alkyl aluminium compounds), in particular methyl aluminiumoxane. Examples of activated supports include methylaluminoxane activated silica and methylaluminoxane activated layered double hydroxide. 
         [0208]    In another embodiment, the activated support may comprise an additional activator being an organo aluminium compound (e.g. alkyl aluminium compound). Suitably, the additional activator is triisobutylaluminium (TIBA) 
         [0209]    As discussed hereinbefore, the present invention also provides a process for forming a polyolefin (e.g. a polyethylene) which comprises reacting olefin monomers in the presence of a compound of formula (I) as defined herein and a suitable activator as defined herein. 
         [0210]    In one embodiment, the process for forming a polyolefin may be conducted in homogeneous solution. 
         [0211]    In another embodiment, the process for forming a polyolefin comprises reacting olefin monomers in the presence of a compound of formula (I) as defined herein and a suitable activator, wherein the compound is immobilized on a suitable support, as defined herein. Suitably, the support is an activated support. 
         [0212]    Suitably, the activated support is insoluble under the olefin polymerisation conditions, such that the process for forming a polyolefin proceeds via slurry polymerisation. 
         [0213]    In another embodiment, the olefin monomers are ethene monomers. 
         [0214]    In another embodiment, the olefin monomers are ethene monomers comprising 1-10 wt % of (4-8C) α-olefin (by total weight of the monomers). Suitably, the (4-8C) α-olefin is 1-butene, 1-hexene, 1-octene, or a mixture thereof. 
         [0215]    In another embodiment, the polyolefin is a polyethylene wax, which is formed by reacting ethene monomers and H 2  in the presence of a compound of formula (I) as defined herein and a suitable activator as defined herein. Optionally, quantities of 1-butene may be included together with the ethene monomers and H 2 . 
         [0216]    A person skilled in the art of olefin polymerization will be able to select suitable reaction conditions (e.g. temperature, pressures, reaction times etc.) for such a polymerization reaction. A person skilled in the art will also be able to manipulate the process parameters in order to produce a polyolefin having particular properties. 
         [0217]    In a particular embodiment, the polyolefin is polyethylene. 
       EXAMPLES 
       [0218]    Examples of the invention will now be described, for the purpose of reference and illustration only, with reference to the accompanying figures, in which: 
         [0219]      FIG. 1  shows the  1 H NMR spectroscopy (chloroform-d 1 , 298 K, 400 MHz) of pro-ligand [EB( tBu     2   Flu,I*)H 2 ]. 
         [0220]      FIG. 2  shows the  1 H NMR spectroscopy (chloroform-d 1 , 298 K, 400 MHz) of pro-ligand [ Me     2   Si(Ind*)Cl]. 
         [0221]      FIG. 3  shows the  1 H NMR spectroscopy (chloroform-d 1 , 298 K, 400 MHz) of pro-ligand [ iPr     2   Si(Ind*)Cl]. 
         [0222]      FIG. 4  shows the  1 H NMR spectroscopy (chloroform-d 1 , 298 K, 400 MHz) of pro-ligand [ Me,Propyl Si(Ind*)Cl]. 
         [0223]      FIG. 5  shows the  1 H NMR spectroscopy (chloroform-d 1 , 298 K, 400 MHz) of pro-ligand [SB(Flu,I*)H 2 ]. 
         [0224]      FIG. 6  shows the Molecular structure of [SB( tBu     2   Flu,I*)H 2 ], 50% ellipsoids, hydrogen atoms omitted for clarity; black: carbon, pink: silicon. Selected bond lengths (Å) and angle (°), Si-CH 3  1.863(3), 1.868(3), Si—CHR Ind : 1.939(2), Si—CH Ind : 1.926(2) and HC Flu —Si—CH Ind : 111.34(12). 
         [0225]      FIG. 7  shows the  1 H NMR spectroscopy (chloroform-d 1 , 298 K, 400 MHz) of [SB( tBu     2   Flu,I*)ZrCl 2 ]. 
         [0226]      FIG. 8  shows the  1 H NMR spectroscopy (chloroform-d 1 , 298 K, 400 MHz) of [SB( tBu     2   Flu,I*)HfCl 2 ]. 
         [0227]      FIG. 9  shows the molecular structure of [SB( tBu     2   Flu,I*)ZrCl 2 ]. 
         [0228]      FIG. 10  shows the molecular structure of [SB( tBu     2   Flu,I*)HfCl 2 ]. 
         [0229]      FIG. 11  shows activity vs time for the polymerisation of ethylene using aluminoxane treated silica support: [SB( tBu     2   Flu,I*)ZrCl 2 ] (black square, dashed line) and [(SBI*)ZrCl 2 ] (grey circle, dotted line). Polymerisation conditions: 10 mg of catalyst, 50 mL hexanes, 2 bar, 70° C. and [TIBA] 0 /[Zr] 0 =1000. 
         [0230]      FIG. 12  shows activity vs temperature for the polymerisation of ethylene using aluminoxane treated silica support (SSMAO):[SB( tBu     2   Flu,I*)ZrCl 2 ] (black square, dashed line) and [(SBI*)ZrCl 2]  (grey circle, dotted line). Polymerisation conditions: 10 mg of catalyst, 50 mL hexanes, 2 bar, 1 h and [TIBA] 0 /[Zr] 0 =1000. 
         [0231]      FIG. 13  shows activity vs temperature for the polymerisation of ethylene using aluminoxane treated layered double hydroxide (LDHMAO) supported/[SB( tBu     2   Flu,I*)ZrCl 2]  (black square, full line). Polymerisation conditions: 10 mg of catalyst, 50 mL hexanes, 2 bar, 1 h and [TIBA] 0 /[Zr] 0 =1000. 
         [0232]      FIG. 14  shows the molecular structure of  Et2 SB( tBu     2   Flu,I*)ZrCl 2 . 
         [0233]      FIG. 15  shows the molecular structure of  Me,Prop SB( tBu     2   Flu,I*)ZrCl 2 . 
         [0234]      FIG. 16  shows the molecular structure of SB( tBu     2   Flu,I* ,3-ethyl )ZrCl 2 . 
         [0235]      FIG. 17  shows the molecular structure of SB(Cp,I*)ZrCl 2 . 
         [0236]      FIG. 18  shows the molecular structure of SB(Cp,I*)HfCl 2 . 
         [0237]      FIG. 19  shows the molecular structure of SB(Cp,I*)ZrC(O-2,6-Me 2 —C 6 H 3 ). 
         [0238]      FIG. 20  shows the  1 H NMR spectrum (chloroform-d 1 , 298 K, 400 MHz) of  Et2 SB( tBu     2   Flu,I*)ZrCl 2 . 
         [0239]      FIG. 21  shows the  1 H NMR spectrum (chloroform-d 1 , 298 K, 400 MHz) of  Me,Prop SB( tBu     2   Flu,I*)ZrCl 2 . 
         [0240]      FIG. 22  shows the  1 H NMR spectrum (chloroform-d 1 , 298 K, 400 MHz) of SB( tBu     2   Flu,I* ,3-ethyl )ZrCl 2 . 
         [0241]      FIG. 23  shows the  1 H NMR spectrum (chloroform-d 1 , 298 K, 400 MHz) of SB(Cp,I*)ZrCl 2 . 
         [0242]      FIG. 24  shows the  1 H NMR spectrum (chloroform-d 1 , 298 K, 400 MHz) of SB(Cp,I*)HfCl 2 . 
         [0243]      FIG. 25  shows the  1 H NMR spectrum (chloroform-d 1 , 298 K, 400 MHz) of SB(Cp,I*)ZrCl(O-2,6-Me 2 —C 6 H 3 ). 
         [0244]      FIG. 26  shows activity vs time of polymerisation of ethylene using aluminoxane treated layered double hydroxide supported/SB( tBu     2   Flu,I*)ZrCl 2  (black square, full line). Polymerisation conditions: 10 mg of catalyst, 50 mL hexanes, 2 bar, 1 h and [TIBA] 0 /[Zr] 0 =1000. 
         [0245]      FIG. 27  shows activity vs temperature of polymerisation of ethylene using aluminoxane treated layered double hydroxide supported/SB( tBu     2   Flu,I*)HfCl 2  (black circle, full line) and aluminoxane treated silica supported/SB( tBu     2   Flu,I*)HfCl 2  (black square, full line). Polymerisation conditions: 10 mg of catalyst, 50 mL hexanes, 2 bar, 1 h and [TIBA] 0 /[Zr] 0 =1000. 
         [0246]      FIG. 28  shows activity vs time of polymerisation of ethylene using aluminoxane treated layered double hydroxide supported/SB( tBu     2   Flu,I*)HfCl 2  (black circle, full line) and aluminoxane treated silica supported/SB( tBu     2   Flu,I*)HfCl 2  (black square, full line). Polymerisation conditions: 10 mg of catalyst, 50 mL hexanes, 2 bar, 1 h and [TIBA] 0 /[Zr] 0 =1000. 
         [0247]      FIG. 29  shows activity vs temperature of polymerisation of ethylene using aluminoxane treated layered double hydroxide supported/ Et2 SB( tBu     2   Flu,I*)ZrCl 2  (black square, full line). Polymerisation conditions: 10 mg of catalyst, 50 mL hexanes, 2 bar, 1 h and [TIBA] 0 /[Zr] 0 =1000. 
       Nomenclature 
       [0248]    The nomenclature used herein will be readily understood by the skilled person having regard to the relevant structural formulae. Various abbreviations used throughout are expanded below:
       SB means (Me) 2 Si-bridged. Similarly,  Et2 SB means (Et) 2 Si-bridged   EB means ethylene-bridged   Ind* or I* means per-methyl indenyl   Flu means fluorenyl   tBu means tert-butyl   Me means methyl   Pr means propyl   iPr means isopropyl       
 
         [0257]    Ph means phenyl 
       General Methodology 
       [0258]    All organometallic manipulations were performed under an atmosphere of N2 using standard Schlenk line techniques or a MBraun UNIlab glovebox, unless stated otherwise. All organic reactions were carried out under air unless stated otherwise. Solvents used were dried by either reflux over sodium-benzophenone diketyl (THF), or passage through activated alumina (hexane, Et 2 O, toluene, CH 2 Cl 2 ) using a MBraun SPS-800 solvent system. Solvents were stored in dried glass ampoules, and thoroughly degassed bypassage of a stream of N 2  gas through the liquid and tested with a standard sodium-benzophenone-THF solution before use. Deuterated solvents for NMR spectroscopy of oxygen or moisture sensitive materials were treated as follows: C 6 D 6  was freeze-pump-thaw degassed and dried over a K mirror; d 5 -pyridine and CDCl 3  were dried by reflux over calcium hydride and purified by trap-to-trap distillation; and CD2C12 was dried over 3 A molecular sieves. 
         [0259]      1 H and  13 C NMR spectroscopy were performed using a Varian 300 MHz spectrometer and recorded at 300 K unless stated otherwise.  1 H and  13 C NMR spectra were referenced via the residual protio solvent peak. Oxygen or moisture sensitive samples were prepared using dried and degassed solvents under an inert atmosphere in a glovebox, and were sealed in Wilmad 5 mm 505-PS-7 tubes fitted with Young&#39;s type concentric stopcocks. 
         [0260]    Mass spectra were using a Bruker FT-ICR-MS Apex III spectrometer. 
         [0261]    For Single-crystal X-ray diffraction in each case, a typical crystal was mounted on a glass fibre using the oil drop technique, with perfluoropolyether oil and cooled rapidly to 150 K in a stream of N 2  using an Oxford Cryosystems Cryostream. 1  Diffraction data were measured using an Enraf-Nonius KappaCCD diffractometer (graphite-monochromated MoKα radiation, λ=0.71073 Å). Series of ω-scans were generally performed to provide sufficient data in each case to a maximum resolution of 0.77 Å. Data collection and cell refinement were carried out using DENZO-SMN. 2  Intensity data were processed and corrected for absorption effects by the multi-scan method, based on multiple scans of identical and Laue equivalent reflections using SCALEPACK (within DENZO-SMN). Structure solution was carried out with direct methods using the program Superflip 3  within the CRYSTALS software suite. 4  In general, coordinates and anisotropic displacement parameters of all non-hydrogen atoms were refined freely except where this was not possible due to the presence of disorder. Hydrogen atoms were generally visible in the difference map and were treated in the usual manner 5 . 
       Synthesis of Unsymmetrical Pro-ligands 
       [0262]    Synthesis of ethylene-bridged [EB( tBu     2   Flu,I*)H 2 ] 
         [0263]    Having regard to Scheme 1 shown below, reaction of one equivalent of [(Ind # )H] with an excess of 1,2-dibromoethane afforded [(Ind*)CH 2 CH 2 Br] which was reacted with one equivalent of [( tBu     2   Flu)Li] to afford the new ethylene-bridged pro-ligand, [EB( tBu     2   Flu,I*)H 2 ], as a colourless solid in good yield.  FIG. 1  provides the  1 H NMR spectrum for EB( tBu     2   Flu,I*)H 2 ]. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    Synthesis of Silicon-Bridged [SB( tBu     2   Flu,I*)H 2 ], [SB(Flu,I*)H 2 ] and [SB( Me,Ph Ind,I*)H 2 ] 
         [0264]    Having regard to Scheme 2 shown below, various silicon-bridged unsymmetrical pro-ligands were accessed using the silane synthon, [ R,R′ Si(Ind*)Cl].  FIGS. 2, 3 and 4  show the  1 H NMR spectra for [ Me     2   Si(Ind*)Cl], [ iPr     2   Si(Ind*)Cl] and [ Me,Pr Si(Ind*)Cl] respectively. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0265]    Having regard to Scheme 3 shown below, the synthesised silane synthon [ Me     2   Si(Ind*)Cl] was separately reacted with one equivalent of [( tBu     2   Flu)Li], [(Flu)Li], and [( Me,Ph Ind*)Li] to afford the new Si-bridged pro-ligands [SB( tBu     2   Flu,I*)H 2 ], [SB(Flu,I*)H 2 ] and [SB( Me,Ph Ind,I*)H 2 ] respectively as colourless solids in very good yields.  FIG. 5  shows the  1 H NMR spectrum for [SB(Flu,I*)H 2 ].  FIG. 6  shows the X-ray crystallographic structure for [SB( tBu     2   Flu,I*)H 2 ]. 
         [0000]    
       
                 
         
             
             
         
       
     
       Synthesis of Unsymmetrical Pro-Catalysts 
       [0266]    Synthesis of [SB( tBu     2   Flu,I*)ZrCl 2 ] and [SB( tBu     2   Flu,I*)HfCl 2 ] 
         [0267]    Having regard to Scheme 4 shown below, stoichiometric reactions of [SB( tBu     2   Flu,I*)Li 2 ] with MCl 4  (M=Zr and Hf) were carried out in benzene at room temperature overnight to afford [SB( tBu     2   Flu,I*)MCl 2 ] as bright orange solids in good yields.  FIGS. 7 and 8  show the  1 H NMR spectra of [SB( tBu     2   Flu,I*)ZrCl 2 ] and [SB( tBu     2   Flu,I*)HfCl 2 ] respectively. Single crystals of [SB( tBu     2   Flu,I*)ZrCl 2 ] and [SB( tBu     2   Flu,I*)HfCl 2 ] suitable for X-ray crystallography were obtained by crystallisation in n-hexane solution at −30 ° C.  FIGS. 9 and 10  show the X-ray crystallographic structures for [SB( tBu     2   Flu,I*)ZrCl 2 ] and [SB( tBu     2   Flu,I*)HfCl 2 ] respectively 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    Synthesis of  Et2 SB( tBu     2   Flu,I*)ZrCl 2  and  Me,Prop SB( tBu     2   Flu,I*)ZrCl 2    
         [0268]    Having regard to Scheme 5 outlined below,  Et2 SB( tBu     2   Flu,I*)ZrCl 2  and  Me,Prop SB( tBu     2   Flu,I*)ZrCl 2  Si-bridged Zr pro-catalysts were prepared in 18% and 41% yields respectively. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    Synthesis of SB( tBu     2   Flu,I* ,3-Ethyl )ZrCl 2    
         [0269]    Having regard to Scheme 6 outlined below, SB( tBu     2   Flu,I* ,3-Ethyl )ZrCl 2  Si-bridged Zr pro-catalyst was prepared. 
         [0000]    
       
                 
         
             
             
         
       
     
       Synthesis of SB(Cp,I*)ZrCl 2    
       [0270]    Having regard to Scheme 7 below, toluene (40 ml) was added to a LiCp (246 mg, 3.41 mmol) and Ind*SiMe 2 Cl (1 g, 3.41 mmol) were added to a Schlenk tube, dissolved in −5° C. THF (50 mL) and left to stir for two hours.  n BuLi (4.7 mL, 1.6 M in hexanes, 7.51 mmol) was added, dropwise, over 30 minutes and the reaction left to stir for 12 hours. The solvent was removed in vacuo and the residue washed with pentane (3×40 mL) and dried to afford a grey powder. One equivalent of ZrCl 4  (796 mg, 3.41 mmol) was added and the mixture dissolved in benzene and left to stir for sixty hours. The solution changed colour from green, to orange and finally red/brown. The solvent was removed under vacuum and the product extracted with pentane (3×40 mL) and filtered through Celite. The filtrate was concentrated in vacuo and stored at −34° C. This yielded SB(Cp,I*)ZrCl 2  as an orange/brown precipitate in 23% yield (365 mg, 0.76 mmol). Orange crystals, suitable for single crystal X-ray diffraction, were grown from a concentrated solution in hexanes at −34 ° C. 
         [0271]      1 H NMR (d 6 -benzene): δ 6.59 (2H, dm, CpH), 5.60 (2H, dm, CpH), 2.52 (3H, s, ArMe), 2.48 (3H, s, ArMe), 2.26 (3H, s, ArMe), 2.15 (3H, s, ArMe), 2.05 (3H, s, ArMe), 1.97 (3H, s, ArMe), 0.72 (3H, s, SiMe), 0.64 (3H, s, SiMe). 
         [0272]      13 C{ 1 H} NMR (d 6 -benzene): δ 135.65 (Ar), 135.13 (Ar), 134.86 (Ar), 131.11 (Ar), 131.50 (Ar), 131.15 (Ar), 129.16 (Ar), 126.35 (Ar), 125.92 (ArSi), 115.87 (CpH), 106.49 (CpH), 84.01 (CpSi), 21.69 (ArMe), 17.91 (ArMe), 17.64 (ArMe), 17.16 (ArMe), 16.92 (ArMe), 15.97 (ArMe), 5.59 (SiMe), 3.26 (SiMe). 
         [0273]    MS (EI): Predicted: m/z 482.0372. Observed: m/z 482.0371.IR (KBr) (cm −1 ): 2961, 2925, 1543, 1260, 1029, 809, 668. 
         [0274]    CHN Analysis (%): Expected: C 54.74, H 5.85, Found: C 54.85, H 5.94. 
         [0000]    
       
                 
         
             
             
         
       
     
       Synthesis of SB(Cp,I*)HfCl 2    
       [0275]    Having regard to Scheme 8 below, SB(Cp,I*)Li 2  (1 g, 2.99 mmol) and HfCl 4  (958 mg, 2.99 mmol) were added to a Schlenk tube. Benzene (100 mL) was added and the reaction was left to stir for 60 hours. The solution changed colour from brown to yellow. The solvent was the removed under vacuum and the product was extracted with pentane (3×40 mL) and filtered through Celite. The filtrate was concentrated in vacuo and stored at −34 ° C. yielding SB(Cp,I*)HfCl 2  as yellow crystals, suitable for single crystal X-ray diffraction, in 24% yield (360 mg, 0.632 mmol). 
         [0276]      1 H NMR (d 6 -benzene): δ 6.54 (3H, dm, CpH), 5.53 (3H, dm, CpH), 2.57 (3H, s, ArMe), 2.56 (3H, s, ArMe), 2.25 (3H, s, ArMe), 2.20 (3H, s, ArMe), 2.09 (3H, s, ArMe), 2.03 (3H, s, ArMe), 0.65 (3H, s, SiMe), 0.57 (3H, s, SiMe). 
         [0277]      13 C{ 1 H} NMR (d 6 -benzene): δ 134.55 (Ar), 134.18 (Ar), 133.51 (Ar), 131.73 (Ar), 131.05 (Ar), 129.64 (Ar), 126.23 (Ar), 125.18 (Ar), 124.38 (Ar), 113.33 (C p H), 107.32 (C p H), 82.33 (C p Si), 21.53 (ArMe), 17.68 (ArMe), 17.37 (ArMe), 16.77 (ArMe), 16.64 (ArMe), 15.51 (ArMe), 5.00 (SiMe), 3.00 (SiMe). 
         [0278]    MS (EI): Predicted: m/z 570.0785. Observed: m/z 570.0701. IR (KBr) (cm −1 ): 2960, 2923, 1542, 1262, 1028, 812, 670. 
         [0279]    CHN Analysis (%): Expected: C 46.36, H 4.95, Found: C 46.52, H 5.04. 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    Synthesis of SB(Cp,I*)ZrCl(O-Me 2 -C 6 H 3 ) 
         [0280]    Having regard to Scheme 9 below, SB(Cp,I*)ZrCl 2  (100 mg, 0.207 mmol) and 2,6-dimethyl potassium phenoxide (66 mg, 0.414 mmol) were added to a Schlenk tube, dissolved in benzene (20 mL), and left to stir for sixteen hours. The solvent was removed in vacuo and the product extracted with pentane (2×20 mL). The  1 H NMR spectra showed resonances corresponding to a mixture of two isomers. Thin, yellow crystals of isomer (a), suitable for single crystal X-ray diffraction were obtained when the solution was concentrated and stored in a −34 ° C. freezer. Purity was 94% by  1 H NMR spectroscopy and crystals were obtained in 15% yield (16 mg, 0.028 mmol). 
       Isomer (a): 
       [0281]      1 H NMR (d 6 -benzene): δ 7.06 (2H, dd, Ar phen H), 6.82 (1 H, t, Ar phen H), 6.26 (1 H, m, CpH), 6.13 (1H, m, CpH), 5.93 (1H, m, CpH), 5.61 (1H, m, CpH), 2.34 (3H, s, ArMe), 2.24 (3H, s, ArMe), 2.22 (6H, s, Ar phen Me), 2.19 (3H, s, ArMe), 2.18 (3H, s, ArMe), 2.15 (3H, s, ArMe), 1.99 (3H, s, ArMe), 0.81 (3H, s, SiMe), 0.75 (3H, s, SiMe). 
       Isomer (b): 
       [0282]      1 H NMR (d 6 -benzene): δ 6.88 (2H, dd, Ar phen H), 6.69 (1 H, t, Ar phen H), 6.51 (1 H, m, CpH), 6.02 (1H, m, CpH), 5.88 (1H, m, CpH), 5.80 (1H, m, CpH), 2.61 (3H, s, ArMe), 2.42 (6H, s, Ar phen Me), 2.40 (3H, s, ArMe), 2.08 (3H, s, ArMe), 1.99 (3H, s, ArMe), 1.64 (3H, s, ArMe), 1.48 (3H, s, ArMe), 0.64 (3H, s, SiMe), 0.61 (3H, s, SiMe). 
         [0000]    
       
                 
         
             
             
         
       
     
       Synthesis of Supported Catalyst Systems 
       [0283]    Synthesis of SSMAO/[SB( tBu     2   Flu,I*)ZrCl 2 ] Catalyst System 
         [0284]    Toluene (40 ml) was added to a Schlenk tube containing silica supported MAO, (SSMAO) (400 mg) and [SB( tBu     2   Flu,I*)ZrCl 2]  (7.8 mg) at room temperature. The slurry was heated to 60° C. and left, with occasional swirling, for one hour during which time the solution turned colourless and the solid colourised dark red. The resulting suspension was then left to cool down to room temperature and the toluene solvent was carefully filtered and removed in vacuo to obtain SSMAO/[SB( tBu     2   Flu,I*)ZrCl 2 ] catalyst as a peach, free-flowing powder. Yield: 353 mg. 
         [0000]    Synthesis of LDHMAO/[SB( tBu     2   Flu,I*)ZrCl 2 ] Catalyst System 
         [0285]    Toluene (40 ml) was added to a Schlenk tube containing layered double hydroxide supported MAO (LDHMAO) (400 mg) and [SB( tBu     2   Flu,I*)ZrCl 2 ] (7.2 mg) at room temperature. The slurry was heated to 60° C. and left, with occasional swirling, for one hour during which time the solution turned colourless and the solid colourised brown. The resulting suspension was then left to cool down to room temperature and the toluene solvent was carefully filtered and removed in vacuo to obtain LDHMAO/[SB( tBu     2   Flu,I*)ZrCl 2 ] catalyst as an off-white, free-flowing powder. Yield: 292 mg. 
       Ethylene Polymerisation Studies 
     Homogeneous Solution Polymerisation 
       [0286]    Unsymmetrical [SB( tBu     2   Flu,I*)ZrCl 2 ], and [SB( tBu     2   Flu,I*)HfCl 2 ]) complexes were tested for their ethylene polymerisation activity against the symmetrical comparator compound rac-[(SBI*)ZrCl 2]  under solution conditions in the presence of tri(isobutyl)aluminium (TIBA) and methylaluminoxane, an aluminium-based scavenger. The reactions were performed under 2 bar of ethylene in a 200 mL ampoule, with around 1 mg of the complex in 50 mL of hexane. The reactions were run for a certain time at 70° C. controlled by heating in an oil bath. The resulting polyethylene was immediately filtered under vacuum through a dry sintered glass frit. The polyethylene product was then washed with pentane (2×25 ml) and then dried on the frit for at least one hour. 
         [0287]    Table la shown below compares the activity of [SB( tBu     2   Flu,I*)ZrCl 2 ], and [SB( tBu     2   Flu,I*)HfCl 2 ]) in homogeneous solution ethylene polymerisation with various symmetrical prior art complexes. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1a 
               
             
             
               
                   
               
               
                 Activity results (kg PE /mol complex /h/bar) for the polymerisation 
               
               
                 of ethylene in homogeneous solution 
               
             
          
           
               
                   
                 T 
                 P 
                 [Al scavenger ]/ 
                   
                 V 
                 n 
                 Activity 
               
               
                 Complex 
                 (° C.) 
                 (bar) 
                 [Zr] a   
                 Al b   
                 (mL) c   
                 (μmol) d   
                 kg PE /mol complex /h/bar 
               
               
                   
               
             
          
           
               
                 [SB( tBu     2   Flu,I*)ZrCl 2 ] 
                 70 
                 2 
                 2000 
                 MAO 
                 50 
                 2.88 
                 35056 
               
               
                 [SB( tBu     2   Flu,I*)HfCl 2 ] 
                 70 
                 2 
                 2000 
                 MAO 
                 50 
                 0.89 
                 9376 
               
               
                 rac-[(SBI*)ZrCl 2 ] 
                 70 
                 2 
                 2000 
                 MAO 
                 50 
                 4.70 
                 4578 
               
               
                 rac-[(EBI*)ZrCl 2 ]† 
                 70 
                 10 
                 10000 
                 MMAO 
                 1800 
                 2.90 
                 42664 
               
               
                 meso-[(EBI*)ZrCl 2 ]† 
                 70 
                 10 
                 10000 
                 MMAO 
                 1800 
                 2.90 
                 26371 
               
               
                 rac-[(EBI*)HfCl 2 ]† 
                 70 
                 10 
                 10000 
                 MMAO 
                 1800 
                 2.00 
                 1248 
               
               
                   
               
               
                 †Values obtained from  Organometallics  2011, 30, 800 
               
               
                   a molar ratio of MAO or MMAO and zirconium complex e.g. [MAO] 0 /[[EBI*ZrCl 2 ] 0 . 
               
               
                   b aluminium scavenger used (MAO or MMAO). 
               
               
                   c volume of solvent, 50 mL of hexane or 1800 mL of isobutene. 
               
               
                   d number of mol of the complex used. 
               
             
          
         
       
     
         [0288]    Having regard to the data presented in Table 1a, unsymmetrical complex [SB( tBu     2   Flu,I*)ZrCl 2 ] is seen to be 7.6 times faster than the similar symmetrical zirconium complex rac-[(SBI*)ZrCl 2 ] in the same conditions (35056 vs. 4578 kg PE /mol complex /h/bar respectively). Unsymmetrical complex [SB( tBu     2   Flu,I*)HfCl 2 ] is 7.5 times faster than the symmetrical hafnium complex rac-[(EBI*)HfCl 2 ] (9377 vs. 1248 kg PE /mol complex /h/bar respectively), even when the data for the unsymmetrical complexes were obtained in far less solvent volume and amount of scavenger. Unsymmetrical complex [SB( tBu     2   Flu,I*)ZrCl 2 ] is 1.3 times faster than meso-[(EBI*)ZrCl 2 ] (42664 vs. 26371 kg PE /mol complex /h/bar respectively), even when the data for the unsymmetrical complexes were obtained in far less solvent volume and amount of scavenger. 
         [0289]    Table 1b shown below compares the activity of various compounds of the invention as catalysts for the homogeneous solution phase polymerisation of ethylene. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1b 
               
             
             
               
                   
               
               
                 Activity results (kg PE /mol complex /h/bar) for the polymerisation of ethylene in homogeneous solution 
               
             
          
           
               
                   
                 T 
                 P 
                 [MAO]/ 
                 Time 
                 V 
                 n 
                 Activity 
               
               
                 Complex 
                 (° C.) 
                 (bar) 
                 [Zr] a   
                 (minutes) 
                 (mL)  b   
                 (μmol)  c   
                 kg PE /mol complex /h/bar 
               
               
                   
               
             
          
           
               
                   Et2 SB( tBu     2   Flu,I*)ZrCl 2   
                 70 
                 2 
                 2000 
                 1 
                 50 
                 0.69 
                 26681 
               
               
                   Et2 SB( tBu     2   Flu,I*)ZrCl 2   
                 70 
                 2 
                 2000 
                 0.5 
                 50 
                 0.69 
                 32712 
               
               
                   Et2 SB( tBu     2   Flu,I*)ZrCl 2   
                 60 
                 2 
                 2000 
                 1 
                 50 
                 0.69 
                 20044 
               
               
                   Et2 SB( tBu     2   Flu,I*)ZrCl 2   
                 80 
                 2 
                 2000 
                 1 
                 50 
                 0.69 
                 20521 
               
               
                   Me,Prop SB( tBu     2   Flu,I*)ZrCl 2   
                 70 
                 2 
                 2000 
                 1 
                 50 
                 0.69 
                 17267 
               
               
                   Me,Prop SB( tBu     2   Flu,I*)ZrCl 2   
                 70 
                 2 
                 2000 
                 0.5 
                 50 
                 0.69 
                 32538 
               
               
                   Me,Prop SB( tBu     2   Flu,I*)ZrCl 2   
                 60 
                 2 
                 2000 
                 1 
                 50 
                 0.69 
                 21041 
               
               
                 SB( tBu     2   Flu,I* ,3-ethyl )ZrCl 2   
                 70 
                 2 
                 2000 
                 1 
                 50 
                 0.71 
                 18676 
               
               
                 SB( tBu     2   Flu,I* ,3-ethyl )ZrCl 2   
                 80 
                 2 
                 2000 
                 1 
                 50 
                 0.71 
                 18846 
               
               
                 SB( tBu     2   Flu,I* ,3-ethyl )ZrCl 2   
                 60 
                 2 
                 2000 
                 1 
                 50 
                 0.71 
                 17570 
               
               
                 SB( tBu     2   Flu,I* ,3-ethyl )ZrCl 2   
                 70 
                 2 
                 2000 
                 0.5 
                 50 
                 0.71 
                 26717 
               
               
                 SB(Cp,I*)ZrCl 2   
                 50 
                 2 
                 1000 
                 5 
                 50 
                 1.04 
                 5410 
               
               
                 SB(Cp,I*)ZrCl 2   
                 60 
                 2 
                 1000 
                 5 
                 50 
                 1.04 
                 5482 
               
               
                 SB(Cp,I*)ZrCl 2   
                 70 
                 2 
                 1000 
                 5 
                 50 
                 1.04 
                 4807 
               
               
                 SB(Cp,I*)ZrCl 2   
                 80 
                 2 
                 1000 
                 5 
                 50 
                 1.04 
                 4709 
               
               
                 SB(Cp,I*)HfCl 2   
                 80 
                 2 
                 1000 
                 5 
                 50 
                 1.04 
                 3055 
               
               
                   
               
               
                   a molar ratio of MAO and zirconium complex. 
               
               
                   b  volume of solvent (hexanes). 
               
               
                   c  number of mol of the complex used. 
               
             
          
         
       
     
         [0290]    From the data presented in Table 1b, it is clear that all complexes based on tert-butyl fluorine demonstrated extremely high activity (all above 17000 kg PE /mol complex /h/bar) for polymerisation ran for 1 minute or 30 seconds. The zirconium cyclopentadienyl compounds gave high activity for polymerisation carried out for 5 minutes (all above 4700 kg PE /mol complex /h/bar). 
       Slurry Polymerisation 
       [0291]    SSMAO/[SB( tBu     2   Flu,I*)ZrCl 2 ], and LDHMAO/[SB( tBu     2   Flu,I*)ZrCl 2 ]) supported catalyst systems were tested for their ethylene polymerisation activity under slurry conditions in the presence of tri(isobutyl)aluminium (TIBA), an aluminium-based scavenger. The reactions were performed under 2 bar of ethylene in a 200 mL ampoule, with 10 mg of the catalyst suspended in 50 mL of hexane. The reactions were run for 60 minutes at a temperature controlled by heating in an oil bath. The resulting polyethylene was immediately filtered under vacuum through a dry sintered glass frit. The polyethylene product was then washed with pentane (2×25 ml) and then dried on the frit for at least one hour. The tests were carried out at least twice for each individual set of polymerisation conditions. 
         [0292]    Table 2 shown below and  FIG. 11  provide activity results (kg PE /mol complex /h/bar) vs time for the slurry polymerisation of ethylene using SSMAO/[complex]. Polymerisation conditions: 10 mg catalyst, 50 mL hexanes, 2 bar, 70 ° C. and [TIBA] 0 /[Zr] 0 =1000. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Activity results (kg PE /mol complex /h/bar) for the slurry polymerisation 
               
               
                 of ethylene using SSMAO/[complex] 
               
             
          
           
               
                   
                 Time (minutes) 
               
             
          
           
               
                 Complex 
                 15 
                 30 
                 60 
                 120 
               
               
                   
               
               
                 [SB( tBu   2 Flu,I*)ZrCl 2 ] 
                 1121 ± 44 
                 1014 ± 20  
                 973 ± 4  
                 898 ± 22 
               
               
                 [(rac-SBI*)ZrCl 2 ] 
                  709 ± 21 
                 669 ± 108 
                 625 ± 31 
                 497 ± 47 
               
               
                   
               
             
          
         
       
     
         [0293]    Table 3 shown below and  FIG. 12  provide activity results (kg PE /mol complex /h/bar) vs temperature for the slurry polymerisation of ethylene using SSMAO/[complex]. Polymerisation conditions: 10 mg catalyst, 50 mL hexanes, 2 bar, 70° C. and [TIBA] 0 /[Zr] 0 =1000. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Activity results (kg PE /mol complex /h/bar) for the slurry polymerisation of 
               
               
                 ethylene using SSMAO/[complex] 
               
             
          
           
               
                   
                 Temperature (° C.) 
               
             
          
           
               
                 Complex 
                 50 
                 60 
                 70 
                 80 
                 90 
               
               
                   
               
               
                 [SB( tBu   2 Flu,I*)ZrCl 2 ] 
                 491 ± 5  
                 607 ± 4  
                 973 ± 4  
                 1340 ± 9  
                 1191 ± 15 
               
               
                 [(rac-SBI*)ZrCl 2 ] 
                 591 ± 12 
                 651 ± 28 
                 669 ± 108 
                 759 ± 24 
                  637 ± 20 
               
               
                   
               
             
          
         
       
     
         [0294]    Having regard to the data provided in Tables 2 and 3, and in  FIGS. 11 and 12 , the unsymmetrical catalyst SSMAO/[SB( tBu     2   Flu,I*)ZrCl 2 ] of the present invention is 1.5 to 2.0 times faster than the similar symmetrical SSMAO/rac-[(SBI*)ZrCl 2 ] comparative system under typical industrial ethylene polymerisation conditions (temperature: 70-80 ° C., time of polymerisation: 1-2 h). 
         [0295]    Table 4 shown below and  FIG. 13  provide activity results (kg PE /mol complex /h/bar) vs temperature for the slurry polymerisation of ethylene using LDHMAO/[SB( tBu     2   Flu,I*)ZrCl 2 ]. Polymerisation conditions: 10 mg catalyst, 50 mL hexanes, 2 bar, 1 h and [TIBA] 0 /[Zr] 0 =1000. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Activity results (kg PE /mol complex /h/bar) for the slurry polymerisation 
               
               
                 of ethylene using LDHMAO/[complex] 
               
             
          
           
               
                   
                 Temperature (° C.) 
               
             
          
           
               
                 Complex 
                 50 
                 60 
                 70 
                 80 
                 90 
               
               
                   
               
               
                 [SB( tBu   2 Flu, 
                 430 ± 42 
                 687 ± 144 
                 932 ± 268 
                 951 ± 4 
                 1542 ± 182 
               
               
                 I*)ZrCl 2 ] 
               
               
                   
               
             
          
         
       
     
         [0296]      FIGS. 26 to 29  provide slurry ethylene polymerisation activity data for SB( tBu     2   Flu,I*)ZrCl 2 , SB( tBu     2   Flu,I*)HfCl 2  and  Et2 SB( tBu     2   Flu,I*)ZrCl 2  when supported on aluminoxane treated layered double hydroxide or aluminoxane treated silica. 
         [0297]    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 
       [0298]    1 J. Cosier, A. M. Glazer, J. Appl. Cryst. 19 (1986) 105 
         [0299]    2 Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1997) 307 
         [0300]    3 L. Palatinus, G. Chapuis, J. Appl. Cryst. 40 (2007) 786 
         [0301]    4 P. W. Betteridge, J. R. Carruthers, R. I. Cooper, K. Prout, D. J. Watkin, J. Appl. Cryst. 36 (2003) 1487 
         [0302]    5 R. I. Cooper, A. L. Thompson, D. J. Watkin, J. Appl. Cryst. 43 (2010) 1100