Group IV phosphinimide complexes in catalysis.

Significant progress has been made in various aspects of the chemistry of Group IV phosphinimide complexes, particularly in their use as highly active catalysts for olefin polymerization upon activation by an appropriate Lewis acid. Advances in synthetic methods have provided routes for the preparation of phosphinimide amide inorganic and organometallic products via metathesis or protonation methods. Testing of TiCp(NPtBu 3)X2 (X = Cl, Me, NMe2) as hydroamination catalysts has shown that these complexes are inactive for this purpose under the conditions employed. In addition, numerous synthetic endeavours have revealed that the titanium phosphinimide complexes are reluctant to form isolable imide derivatives. However, through efforts to prepare ligand transfer reagents, magnesium phosphinimide complexes have been developed that initiate the polymerization of methyl methacrylate at ambient temperatures, probably via a radical process. Examination of the highly active phosphinimide polymerization catalysts inferred that the presence of a cyclopentadienide ligand, in addition to bulky alkyl groups on the phosphorus atom, was beneficial to prolong catalytic activity. In an effort to use catalysts that encompass this apparent advantage while preparing polymers of different composition that remain of industrial value, a series of bimetallic titanium complexes of the general formula p-(CH2PR2NTiCp'X 2)2C6H4 (Cp' = Cp, Cp*; R = tBu, Cy; X = Cl, Me) were prepared. For comparison, their monometallic analogues, TiCp(NPR2Bn)X2, were also synthesized and tested using the same polymerization protocol. Several important features about these catalysts were ascertained upon examination of the polymer properties. Typically, high catalytic activities were observed, and low polydispersity polymers were generated when the discrete activator [Ph3C][B(C 6F5)4] was used. However, use of MAO as the activator in the presence of precatalysts that have a phosphinimide ligand with a benzyl substituent resulted in polymers with a broad molecular weight distribution. Another observation that transpired from this series of polymerization experiments was that the activity increased as the steric bulk of the ligands increased. Finally, a systematic investigation into the synthesis and utility of zirconium phosphinimide complexes as olefin polymerization catalysts was performed. (Abstract shortened by UMI.) Source: Dissertation Abstracts International, Volume: 66-07, Section: B, page: 3705. Thesis (Ph.D.)--University of Windsor (Canada), 2003.

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