Use of heterocycle borate metal complexes as coordination polymerization catalysts

Abstract: Novel hydridotris(pyrazolyl)borate complexes of Group 4 metals of the Periodic Table of Elements are coordination polymerization catalysts. The complexes are of the formula HY·M·X′ n ·X₃ (I) or [HY·M·X′ n ·X₂]⁺ A⁻ (II) wherein:- HY is a hydridotris(pyrazolyl)borate ion in which the pyrazolyl group can be substituted by, for example, C₁-C₆ alkyl; M is a Group 4 metal, especially titanium or zirconium; each X is an inert anionic ligand, especially OR in formula I and R in formula II, wherein R is phenyl or C₁-C₆ alkyl or cycloalkyl; X′ is an inert neutral donor ligand; n is 0 or 1, preferably 0; and A⁻ is a noncoordinating, compatible anion. When the complex is of formula I, it is used with an aluminum compound containing Al-O, Al-N or Al-P bonds, especially an alkylaluminoxane, and, optionally, a tri(C₁-C₆ alkyl)aluminum compound.

Description: The present invention pertains to the use of hydriodotris(pyrazolyl)borate complexes of Group 4 metals of the Periodic table of the Elements as coordination polymerization catalysts for polymerizing vinyl aromatic monomers, particularly styrene, to produce syndiotactic polymers. In US-A-4,808,680 a process for preparing syndiotactic polystyrene utilizing cyclopentadienyl zirconium trialkoxides, trihalides, etc. and polymethylaluminoxane was disclosed. Complexes having a similar or increased catalytic effectiveness but lacking in cyclopentadienyl functionality have been sought without success. The present inventor has now discovered such complexes. CA 85:103138k (Kouba et al; Inorg Chem, 15, (9), 1976, 2313-14) discloses the synthesis of poly(1-pyrazolyl)borate titanium complexes of the formulae: (i) HB(C 3 N 2 H 3 ) 3 TiCl; (ii) HB(3,5-(CH 3 ) 2 C 3 N 2 H) 3 TiCl; (iii) HB(C 3 N 2 H 3 ) 3 TiCl 2 (THF); (iv) [HB(C 3 N 2 H 3 ) 3 TiCl(OCH 3 )] 2 ; or (v) HB(C 3 N 2 H 3 ) 3 TiCl 2 (C 3 N 2 H 4 ). The complexes of formulae i and ii were obtained by reacting K[HB(C 3 N 2 H 3 ) 3 ] and K[HB(3,5-(CH 3 ) 2 C 3 N 2 H) 3 ] with TiCl 4 ; the complex of formula iii was obtained by Na(Hg) reduction of HB(C 3 N 2 H 3 ) 3 TiCl 3 ; and the complexes of formulae iv and v were obtained by reaction of methanolic TiCl 4 with K[HB(C 3 N 2 H 3 ) 3 ]. CA 98:136560p (Reger et al; Inorg Chem, 22, (7), 1983, 1064-8) discloses the synthesis of zirconium(IV) poly(pyrazolyl)borate tert-butoxide derivatives of the formulae: RB(C 3 N 2 H 3 ) 3 Zr(O-C(CH 3 ) 3 )Cl 2 or HB(3,5-(CH 3 ) 2 C 3 N 2 H)) 3 Zr(O-C(CH 3 ) 3 )Cl 2 wherein R is CH 3 (CH 2 ) 2 CH 2 or (CH 3 ) 2 CH 2 , by reaction of RB(C 3 N 2 H 3 ) 3 ZrCl 3 or HB(3,5-(CH 3 ) 2 C 3 N 2 H)) 3 ZrCl 3 with KOC(CH 3 ) 3 ). CA 111:69728w (Kresinski et al; Polyhedron, 8, (6), 1989, 845-7) discloses the synthesis of tris[3,5-dimethylpyrazol-l-ylboratotris(aryloxo)zirconium (IV) complexes of the formula: Zr(HB(3,5-(CH 3 ) 2 C 3 N 2 H) 3 )(OC 6 H 4 Z) 3 ] wherein Z is H, 3-NO 2 , 4-NO 2 , 2-F, 3-F, 4-F or 4-C(CH 3 ) 3 , by reaction of ZC 6 H 4 OH with Zr(HB(3,5-(CH 3 ) 2 C 3 N 2 H) 3 )Cl 3 in the presence of a base CA 111:186250v (Hughes et al; J Chem Soc Dalton Trans, (7), 1989, 1413-16) discloses the synthesis of dichloro-[trimethylhydrazido(1-)]-[tris(pyrazolyl)borato]titanium (IV) and dichloro[N-phenylhydrazido(1-)-N]-[tris-(pyrazolyl)borato]titanium (IV) by reacting trichloro[tris-(pyrazolyl)borato]titanium (IV) with trimethylhydrazine or N-phenylhydrazine. US-A-4870042 discloses an olefin polymerization catalyst comprising (i) a catalyst component obtained by reacting an alkali metal boron hydride with pyrazole and subsequently reacting the reaction product with a Group IVb metal compound, and (ii) aluminoxane. According to the present invention there is now provided a polymerization process for preparing syndiotactic polymers wherein at least one vinyl aromatic monomer is contacted with a catalyst under coordination polymerization conditions characterized in that the catalyst comprises a complex corresponding to the formula: HY·M·X' n ·X 3 or [HY·M·X' n ·X 2 ] + A - wherein:- HY is a hydridotris(pyrazolyl)borate ion, M is a metal of Group 4 of the Periodic Table of the Elements X each occurrence is an inert anionic ligand selected from R, NR 2 , PR 2 , OR, SR and BR 2 , wherein R each occurrence is an aliphatic, cycloaliphatic or aromatic C 1 - C 12 hydrocarbyl group; X' is an inert, neutral donor ligand selected from ROR, RSR, NR 3 and PR 3 , wherein R is as defined above, and C 2 - C 20 olefins and diolefins; n is 0 or 1; and A - is a noncoordinating, compatible anion containing a single coordination complex comprising a charge-bearing metal or metalloid core, which anion is sufficiently bulky to stabilise the Group 4 cation and sufficiently labile to be displaced by the vinyl aromatic monomer, and, when the complex is of formula I, the catalyst additionally comprises an aluminium compound containing at least one Al-O, Al-N, or Al-P bond. Donor ligands are able to form shared electron bonds but not a formal covalent bond. Preferably n is O. All references to the Periodic Table of the Elements herein shall refer to the Periodic Table of the Elements, published and copyrighted by CRC Press, Inc., 1989. Also, any reference to a Group or Series shall be to the Group or Series as reflected in this Periodic Table of the Elements, utilizing the IUPAC system for numbering groups. Also as used herein, the term "substituted" when used with reference to R means such groups bearing one or more covalently bonded substituents that do not interfere with the essential nature of the principal group and are inert. The term "inert" means noninterfering with the complex's preparation or with the use of the resulting metal complex as a polymerization catalyst. Examples of substituted R groups include: aralkyl, alkaryl, haloalkyl, silylalkyl, haloalkyl, haloaryl, haloalkaryl, halosilyl, haloalkarylsilyl and alkoxyalkyl. By the term "aromatic" is included both substituted and unsubstituted aryl groups. Preferably X in the complexes of formula (I) is in each occurrence OR, and R is selected from phenyl, and C 1-6 alkyl or cycloalkyl groups. Most preferably X each occurrence is C 1-6 alkoxide. Preferably X in the complexes of formula (II) is in each occurrence R, and R is selected from phenyl, and C 1-6 alkyl or cycloalkyl groups. Most preferably X each occurrence is C 1-6 alkyl. Preferably M is titanium or zirconium. Hydridotris(pyrazolyl)borate complexes of Group 4 metals corresponding to formula (I) are prepared by combining an alkali metal hydridotris(pyrazolyl)-borate compound with a halogenated Group 4 metal compound corresponding to the desired complex or subsequently convertible into the desired complex. Thus suitable Group 4 metal compounds correspond to the formula: X"M·X' n ·X 3 , wherein: X" is halo, especially chloro, and M, X', n and X are as previously defined. With respect to the hydridotris(pyrazolyl)borate derivatives, suitable pyrazolyl groups include pyrazolyl itself, that is, as well as inertly substituted monovalent pyrazol derivatives. Examples include C 1-6 alkyl pyrazolyl derivatives such as 3,5-dimethylpyrazolyl and trimethylpyrazolyl. A preferred alkali metal hydridotris(pyrazolyl)borate compound is potassium hydridotris(pyrazolyl)borate. The procedure for preparing the complexes of the invention is analogous to that described in Inorg. Chem., 20, 2983, (1981), J. Amer. Chem. Soc. 89 , 3170 (1967) and J. Amer. Chem. Soc. 91 , 588 (1969). The complex of formula (I) is rendered catalytically effective by combining the same with an aluminum compound containing one or more Al-O, Al-N or Al-P bonds, as previously mentioned. Preferred aluminum compounds are the well known alkylaluminoxanes, also known as polyalkylaluminoxanes. A highly preferred aluminum compound is methylaluminoxane (MAO). Effective coordination catalysts are formed from the complexes of formula (I) in the presence of an aliphatic, cycloaliphatic or aromatic solvent or a combination of such solvents. The components are employed in quantities which provide an atomic ratio of MAO:M from 10:1 to 50,000:1, more suitably from 50:1 to 10,000:1, and most suitably from 100:1 to 1000:1. Alkylaluminoxanes may be prepared according to any known technique. One such technique includes the reaction of a trialkylaluminum, such as trimethyl-aluminum, and a hydrated metal salt as disclosed by Kaminsky in US-A-4,544,762. A preferred technique is the use of a regeneratable aqueous imbiber as disclosed in US-A-5,015,749. For purposes of calculating the molar ratio of MAO:titanium in the catalysts of the present invention, the polymethylaluminoxane is assigned a repeating unit structure corresponding to the formula: (Al(CH 3 )O). The hydridotris(pyrazolyl)borate metal complex and aluminum compound containing one or more Al-O, Al-N, or Al-P bonds and optional aluminum trialkyl compound are combined in a suitable diluent. In the preparation of the catalyst composition, the metal complex is preferably added in an inert diluent to the various aluminum compounds. The catalyst components may be suitably mixed in an inert atmosphere such as nitrogen, argon, xenon, or combinations thereof. The components are mixed at any suitable temperature, preferably from 0°C to 100°C, more suitably from 25°C to 50°C. The metal complex (I) may also be combined with the aluminum containing compounds in the presence of the monomer to be polymerized if desired. A further beneficial effect is also observed both in catalytic efficiency and in rate of catalyst formation if an aluminum trialkyl compound is also incorporated into the catalyst. Examples of suitable trialkyl aluminum compounds include trimethyl aluminum, triethyl aluminum, triisopropyl aluminum and triisobutyl aluminum. A preferred trialkyl aluminum compound is triisobutyl aluminum. The aluminum trialkyl compound may be utilized in an amount to provide an atomic ratio of aluminum trialkyl:M of 0:1 to 50,000:1, more suitably from 50:1 to 10,000:1, and most suitably from 100:1 to 1000:1. The complexes of formula (II) are catalytically effective without the need for a cocatalyst. They are prepared by combining at least two components as hereinafter disclosed. The first component is a derivative of a Group 4 metal containing at least one substituent which will combine with the cation of a second component (described hereinafter) or alternatively which is subject to oxidative activation as hereinafter described. The first component additionally must be capable of forming a cation formally having a coordination number that is one less than its valence. The second component is a salt of a Bronsted acid and a noncoordinating, compatible anion or alternatively a salt of an oxidizing cation and a noncoordinating, compatible anion. As used herein, the recitation "noncoordinating, compatible, oxidatively inert anion" means an anion which either does not coordinate with the first component or a derivative thereof, or which is only weakly coordinated to said component thereby remaining sufficiently labile to be displaced by the monomer to be polymerized. The recitation "noncoordinating, compatible anion" specifically refers to an anion which when functioning as a charge balancing anion does not transfer an anionic substituent or fragment thereof to the cationic portion of the catalyst. Compatible anions are also anions which are not degraded to neutrality under the reaction conditions of the present invention. More preferably such metal derivative compounds are those having organyl substituents that are either devoid of reactive hydrogens or wherein potentially reactive hydrogens are protected by bulky protecting groups. Illustrative, but not limiting examples of suitable metal derivative compounds include: [hydridotris(pyrazolyl)borate]tribenzylzirconium, [hydridotris(pyrazolyl)borate]tribenzyltitanium, [hydridotris(pyrazolyl)borate]trimethyltitanium, [hydridotris(pyrazolyl)borate]trimethylzirconium, [hydridotris(pyrazolyl)borate]trineopentyltitanium, [hydridotris(pyrazolyl)borate]triphenylzirconium, [hydridotris(pyrazolyl)borate]trineopentylzirconium, [hydridotris(pyrazolyl)borate]di(m-tolyl)titanium, [hydridotris(pyrazolyl)borate]di(p-tolyl)zirconium, [hydridotris(pyrazolyl)borate]trimethyltitanium hydride, [hydridotris(pyrazolyl)borate]tri(diphenylmethyl)-zirconium, [hydridotris(pyrazolyl)borate]diphenylmethylzirconium, [hydridotris(pyrazolylborate)]dimethyl-(isopropoxy)-titanium, [hydridotris(pyrazolyl]borate)dibenzyl(isopropoxy)-titanium, [hydridotris(pyrazolyl)-borate]dibenzyl(phenoxy)zirconium, [hydridotris(pyrazolyl)borate]dibenzyl(isopropoxy)zirconium, [hydridotris-(pyrazolyl)borate]dimethyltitanium chloride, [hydridotris(pyrazolyl)borate]methylhafnium chloride, [hydridotris(3,5-dimethylpyrazolyl)borate]tribenzylzirconium, [hydridotris(trimethylpyrazolyl)borate]tribenzyltitanium, [hydridotris(3,5-diethylpyrazolyl)-borate]trimethyltitanium, [hydridotris(trimethylpyrazolyl)borate]trimethylzirconium, [hydridotris(3,5-dimethylpyrazolyl)borate]trineopentyltitanium, [hydridotris(3,5 dimethylpyrazolyl)borate]triphenylzirconium, [hydridotris(trimethylpyrazolyl)borate]trineopentylzirconium, [hydridotris(trimethylpyrazolyl)-borate]dimethyltitanium chloride and [hydridotris(3,5-dimethylpyrazolyl)borate]methylhafnium chloride. Other compounds which are useful in the catalyst compositions of formula (II) will, of course, be apparent to those skilled in the art. Most preferred are titanium compounds. Compounds useful as a second component in the preparation of the complexes of formula (II) may, in one embodiment, comprise a cation, which is a Bronsted acid capable of donating a proton, and a compatible, noncoordinating anion. In another embodiment such compounds comprise an oxidizing cation and a compatible, noncoordinating anion. Said anions are those containing a single coordination complex comprising a charge-bearing metal or metalloid core which anion is relatively large (bulky), capable of stabilizing the active Group 4 cation formed when the two components are combined, and which will be sufficiently labile to be displaced by the polymerizable monomer. The recitation "metalloid", as used herein, includes non-metals such as boron and phosphorus which exhibit semi-metallic characteristics. Suitable metals, include, but are not limited to, aluminum, gold and platinum. Suitable metalloids include, but are not limited to, boron, phosphorus and silicon. Compounds containing anions which comprise coordination complexes containing a single metal or metalloid atom are, of course, well known. In light of this, salts containing anions comprising a coordination complex containing a single boron atom are preferred. Preferably, second components useful in the preparation of the complexes of formula (II) may be represented by the following general formulas: (L-H) + A - or Ox + [A*] - wherein: L is a neutral Lewis base; (L-H) + is a Bronsted acid; A - is a compatible, noncoordinating anion; Ox + is an organic or metallic oxidizing cation; and [A*] - is a compatible, noncoordinating, oxidatively inert, anion. By the term "oxidatively inert" as employed above is meant that A* of formula (IV) comprises an anion which is a single coordination complex comprising a plurality of lipophilic radicals covalently coordinated to and shielding a central formally charge-bearing metal or metalloid atom, which anion is bulky and stable under the oxidation and subsequent polymerization conditions, and which anion is compatible with and noncoordinating towards the resulting polymerization catalyst. The anion is employed only to provide charge balance without interfering with the oxidizing ability of Ox + . Preferably A - corresponds to the formula: [M'Q n' ] - wherein: M' is a metal or metalloid selected from Groups 5-15 of the Periodic Table of the Elements having a valency m; Q independently each occurrence is selected from hydride, dialkylamido, halide, alkoxide, aryloxide, silyl, hydrocarbyl, and fluoro-substituted-hydrocarbyl radicals of up to 20 carbon or silicon atoms with the proviso that in not more than one occurrence is Q halide; n' is an integer from 2 to 8; and n'-m = 1; Second components of formula (III) comprising boron are particularly useful in the preparation of catalysts of the invention and may be represented by the following general formula: [L-H] + [BQ 4 ] - wherein: L is a neutral Lewis base; [L-H]+ is a Bronsted acid; B is boron in a valence state of 3; and Q is as previously defined. Illustrative, but not limiting, examples of boron compounds which may be used as a second component of formula (III) are trialkyl-substituted ammonium salts such as triethylammonium tetraphenylborate, tripropylammonium tetraphenylborate, tri(n-butyl)ammonium tetraphenylborate, trimethylammonium tetra(p-tolylborate), tributylammonium tetrakis-pentafluorophenylborate, tripropylammonium tetrakis-2,4-dimethylphenylborate, tributylammonium tetrakis-3,5-dimethylphenylborate and triethylammonium tetrakis-(3,5-di-trifluoromethylphenyl)borate. Also suitable are N,N-dialkyl anilinium salts such as N,N-dimethylanilinium tetraphenylborate, N,N-diethylanilinium tetraphenylborate and N,N-2,4,6-pentamethylanilinium tetraphenylborate; dialkyl ammonium salts such as di(isopropyl)ammonium tetrakis-pentafluorophenylborate and tri(dimethylphenyl)phosphonium dicyclohexylammonium tetraphenylborate; and triaryl phosphonium salts such as triphenylphosphonium tetraphenylborate, tri(methylphenyl)phosphonium tetrakis-pentafluorophenylborate and tetraphenylborate. Anions comprising boron which are particularly useful as [A*] - may be represented by the following general formula: [BX 1 X 2 X 3 X 4 ] - wherein: B is boron in a valence state of 3; X 1 to X 4 are the same or different nonreactive, organyl or silyl radicals containing from 6 to 20 carbon or silicon atoms. In addition two or more of X 1 to X 4 may be linked to each other through a stable bridging group. Preferably X 1 to X 4 lack reactive hydrogen moieties. That is, the radicals are either devoid of hydrogen, contain only hydrogen in nonactivated positions or contain sufficient steric hindrance to protect potentially active hydrogen sites. Examples of suitable radicals for X 1 to X 4 are perfluorinated hydrocarbyl radicals containing from 1 to 20 carbon atoms. 3,4,5-trifluorophenyl and 3,4-di(trifluoromethyl)phenyl. A most highly preferred compatible, noncoordinating, inert, second component anion corresponding to formula (IV) is tetra(pentafluorophenyl)borate. Suitable oxidizing cations include organic and inorganic cations having sufficient electronegativity to oxidize the metal derivatives. Organic oxidizing cations for use in the compounds corresponding to formula (IV) include ferrocenium ions, indenium ions and cationic derivatives of substituted ferrocene and indene molecules. Suitable metallic oxidizing cations include Ag +1 , Pd +2 , Pt +2 , Hg +2 , Hg 2 +2 , Au + and Cu + . Highly preferred oxidizing cations have an oxidation potential of at least + 0.20 volt and preferably at least + 0.25 volt. Most highly preferred oxidizing cations are ferrocenium and Ag +1 cations. Without wishing to be bound by any particular theory of operation it is believed that the oxidizing cation causes the molecular oxidation of the metal derivative, and in the process becomes a neutral species. The oxidized metal derivative loses a hydrogen or hydrocarbyl radical by a unimolecular elimination reaction. Two or more such radicals form a hydrogen molecule or a neutral organic species. These byproducts are neutral or noninterfering with any subsequent polymerization reaction and may also be removed from the reaction mixture. The preparation technique is analogous to that previously disclosed by R. Jordan, et al., J. Amer. Chem. Soc., 109, 4111-4113 (1987). Illustrative, but not limiting, examples of oxidizing agents for use in the second components of formula (IV) are ferrocenium tetra(pentafluorophenyl) borate, gold (I) tetrakis 3,4,5-trifluorophenyl borate, silver tetra(pentafluorophenyl) borate and 1,1'-dimethylferrocenium tetrakis-3,5-bistrifluoromethylphenyl borate. In general, the complex of formula (II) can be prepared by combining the two components in a suitable solvent at a temperature within the range from 0°C to 100°C, preferably 25°C to 50°C. When utilized as a catalyst the complex can also be formed in situ if the components thereof are added directly to the polymerization process and a suitable solvent or diluent, including condensed monomer, is used in said polymerization process. It is, however, preferred to form the catalyst in a separate step in a suitable solvent prior to adding the same to the polymerization step. The respective components are generally sensitive to both moisture and oxygen and should be handled and transferred in an inert atmosphere such as nitrogen, argon or helium. Suitable solvents or diluents include, but are not necessarily limited to, straight and branched-chain hydrocarbons such as C 6-12 alkanes(eg hexane, heptane and octane); C 6-12 cyclic and alicyclic hydrocarbons such as cyclohexane, cycloheptane, methylcyclohexane and methylcycloheptane, C 6-12 aromatic and alkyl-substituted aromatic compounds such as benzene, toluene, xylene, and decalin, and mixtures of the foregoing. The complexes may be employed as homogeneous catalysts or supported on the surface of a suitable support such as alumina or silica. The catalysts may be employed to polymerize any coordination polymerizable monomer including C 2-10 α-olefins and C 8-12 vinylaromatic monomers. As used herein, the term "syndiotactic" refers to such polymers having a stereoregular structure of greater than 50 percent syndiotactic as determined by 13 C nuclear magnetic resonance spectroscopy. Such polymers may be usefully employed in the preparation of articles and objects (for example, via compression molding or other suitable technique) having an extremely high resistance to deformation due to the effects of temperature. The polymerization is conducted at temperatures of from 25°C to 100°C, preferably from 30°C to 80°C, for a time sufficient to produce the desired polymer. Typical reaction times are from several minutes to several hours, preferably from 1 to 10 hours. The optimum time will vary depending upon the temperature, solvent and other reaction conditions employed. The polymerization of vinyl aromatic monomers is preferably conducted under bulk polymerization conditions. The polymerization can be conducted at subatmospheric pressure as well as superatmospheric pressure, suitably at reduced pressures such that the lowest boiling component or components of the polymerization mixture do not vaporize up to 100 MPa. For the polymerization of α-olefins, especially highly volatile low molecular weight monomers, elevated pressures from 0.2 to 10 MPa are preferred. In the polymerization of vinyl aromatic monomers it is preferable that near atmospheric pressure be employed. Suitable vinyl aromatic monomers which can be polymerized in the process of the present invention include those represented by the formula: wherein each R' is independently hydrogen, an aliphatic, cycloaliphatic or aromatic hydrocarbon group having from 1 to 10, more suitably from 1 to 6, most suitably from 1 to 4, carbon atoms; or a halogen atom. Preferably such monomers include: styrene, chlorostyrene and n-butyl styrene, with styrene being especially suitable. The polymerization can be conducted in the presence of an inert diluent. Examples include aliphatic, cycloaliphatic, aromatic and halogenated aromatic hydrocarbons, as well as mixtures thereof. Preferred diluents comprise the C 4-20 alkanes, especially branched chain alkanes, toluene and mixtures thereof. A particularly desirable diluent for the polymerization is isooctane, or blends thereof such as Isopar-E®, available from Exxon. Suitable amounts of solvent are employed to provide a monomer concentration from 5 percent to 100 percent by weight. During the polymerization, polymer may precipitate from the reaction mixture as it is formed. Preferably vinyl aromatic monomers are polymerized in the absence of a diluent. As in other similar polymerizations it is highly desirable that the monomers and solvents employed be of sufficiently high purity that catalyst deactivation does not occur. Any suitable technique for monomer and diluent purification such as devolatilization at reduced pressures, contacting with molecular sieves or high surface area alumina or deaeration, may be employed. Purification of the resulting polymer to remove entrained catalyst may also be desired by the practitioner. Entrained catalyst may generally be identified by residues of ash on pyrolysis of the polymer that are attributable to aluminum and titanium values. A suitable technique for removing such compounds is by solvent extraction, for example, extraction utilizing hot, high boiling chlorinated solvents, followed by filtration. Having described the invention, the following example is provided as further illustrative and is not to be construed as limiting. EXAMPLE 1 Under a nitrogen atmosphere, a solution of chlorotitanium triisopropoxide (5.21 g. 0.020 mol) in toluene (100 ml) was added dropwise to a slurry of potassium (hydridotris(pyrazolyl)borate) (5.04 g, 0.020 mol) in 150 ml toluene at 25°C. The resulting mixture was stirred for 16 hours at 25°C. A white precipitate was allowed to settle and the solution was transferred to a second container via a cannula. The volatile components were removed under reduced pressure at 60°C leaving a white semi-crystalline solid. Identification of the product as [hydridotris(pyrazolyl)borate]titanium triisopropoxide was made on the basis 1 H and 13 C NMR spectra. The above complex was combined with methylaluminoxane (MAO) and triisobutyl aluminum (TIBA) to prepare a coordination polymerization catalyst. Accordingly, 10 ml of purified and dried styrene monomer, 75 µL of a 1M triisobutyl aluminum solution in toluene and 37.5 µl of a 2M solution of MAO in toluene were combined in a glass lined, polymerization reactor. Thirty seven and one half µL of a 0.01 M solution of [hydridotris(pyrazolyl)-borate]titanium triisopropoxide in toluene was added to initiate the polymerization. The reactor was held at 70°C. for 4 hours. The reaction was quenched with methanol, and the polymer recovered by filtration and drying. The yield was 0.28 g of a highly crystalline polystyrene having a melting point of 266°C. as determined by differential scanning calorimetry, and a syndiotacticity of 90 percent as determined by 13 C NMR spectroscopy. EXAMPLE 2 Under a nitrogen atmosphere, a solution of chlorotitanium triisopropoxide (5.21 gm, 0.020 mol) in 50 ml of toluene was added dropwise to a slurry of potassium [hydridotris(3,5-dimethylpyrazolyl)borate] (6.72 gm, 0.020 mol) in 150 ml of toluene at room temperature. The resulting mixture was stirred overnight at room temperature. A fine white precipitate was present in the solution. The solution was filtered to remove the precipitate and the volatiles removed under reduced pressure at 70°C leaving a white powdery solid. The product was purified by recrystallization from hexane at -10°C. Identification of the product as [hydridotris(3,5-dimethylpyrazolyl)borate]titanium triisopropoxide was made on the basis of the 1 H NMR spectrum. The above complex was combined with MAO and TIBA to prepare a coordination polymerization catalyst. The same conditions as Example 1 were utilized. The yield was 0.43 g of syndiotactic polystyrene having a melting point of 266°C as determined by differential scanning calorimetry.

Claims: A polymerization process for preparing syndiotactic polymers wherein at least one vinyl aromatic monomer is contacted with a catalyst under coordination polymerization conditions characterized in that the catalyst comprises a complex corresponding to the formula: HY·M·X' n ·X 3 or [HY·M·X' n ·X 2 ] + A - wherein:- HY is a hydridotris(pyrazolyl)borate ion, M is a metal of Group 4 of the Periodic Table of the Elements X each occurrence is an inert anionic ligand selected from R, NR 2 , PR 2 , OR, SR and BR 2 , wherein R each occurrence is an aliphatic, cycloaliphatic or aromatic C 1 - C 12 hydrocarbyl group; X' is an inert, neutral donor ligand selected from ROR, RSR, NR 3 and PR 3 , wherein R is as defined above, and C 2 - C 20 olefins and diolefins; n is 0 or 1; and A - is a noncoordinating, compatible anion containing a single coordination complex comprising a charge-bearing metal or metalloid core, which anion is sufficiently bulky to stabilise the Group 4 cation and sufficiently labile to be displaced by the vinyl aromatic monomer, and, when the complex is of formula I, the catalyst additionally comprises an aluminium compound containing at least one Al-O, Al-N, or Al-P bond. A process according to Claim 1, wherein the complex is of formula I. A process according to Claim 2, wherein A - corresponds to the formula: [M'Q n' ] - wherein:- M' is a metal or metalloid selected from Groups 5 to 15 of the Periodic Table of the Elements and has a valency m; Q independently each occurrence is selected from hydride, dialkylamido, halide, alkoxide, aryloxide, silyl, hydrocarbyl or fluoro-substituted-hydrocarbyl radicals of up to 20 carbon or silicon atoms with the proviso that in not more than one occurrence is Q halide; n' is an integer from 2 to 8; and n'-m = 1. A process according to Claim 3, wherein A - is selected from tetraphenylborate; tetra(p-tolylborate); tetrakis (pentafluorophenyl)borate; tetrakis (2,4- dimethylphenyl) borate; tetrakis(3,5-dimethylphenyl)borate; tetrakis(3,5-bis(trifluoromethyl)phenyl)borate; and tetrakis(3,4,5-trifluorophenyl)borate. A process according to Claim 4, wherein A - is tetrakis (pentafluorophenyl) borate. A process according to any one of Claims 2 to 5, wherein each X is OR and R is selected from phenyl and C 1 -C 6 alkyl or cycloalkyl. A process according to Claim 6, wherein each X is C 1 -C 6 alkoxide. A process according to any one of Claims 2 to 7, wherein the aluminum compound is methylaluminoxane. A process according to any one of Claims 2 to 8, wherein the catalyst additionally comprises a tri-(C 1-6 alkyl) aluminum compound. A process according to Claim 1, wherein the complex is of formula II. A process according to Claim 10, wherein each X is selected from phenyl and C 1 -C 6 alkyl or cycloalkyl. A process according to Claim 11, wherein each X is C 1 -C 6 alkyl. A process according to any one of the preceding claims, wherein n is 0. A process according to any one of the preceding claims, wherein M is titanium or zirconium. A process according to any one of the preceding claims, wherein the pyrazolyl moiety of HY is pyrazolyl or 3,5-dimethyl pyrazolyl. A process according to Claim 15, wherein the complex is [hydridotris(pyrazolyl)borate]titanium triisopropoxide or [hydridotris(3,5-dimethylpyrazolyl)borate]titanium triisopropoxide. A process according to any one of the preceding claims, wherein the monomer is styrene. The use of a complex of formula I or formula II as defined in Claim 1 as a coordination polymerization catalyst in the polymerization of a vinyl aromatic monomer. A use according to Claim 18, wherein the complex is as defined in any one of Claims 2 to 7 and 11 to 16.

Inventors: NEWMAN THOMAS H, NEWMAN, THOMAS H.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1991
Main classification: C07F7
IPC codes: C08F4, C08F12, C07F7, C08F10