Dinuclear Group 4 Metallocene Catalysts of the Type [(Cp2M)2(μ-Me)(μ-C2R)]: Structure-Activity Relationships in Ethylene Polymerization.

The heterodinuclear zirconocene/titanocene complexes, [Cp2Zr(μ-Me)(μ-C2R)(TiCp2)] where R = SiMe3 and R = Ph, were prepared using the previously reported comproportion reaction of the zirconocene alkynyl methyl complex with Rosenthal's zirconocene source. Examination of the molecular structure revealed alkynyl group migration from Zr to Ti, as confirmed by single-crystal x-ray analysis, nuclear magnetic resonance spectroscopy, and quantum chemical calculations. The homodinuclear (Zr/Zr) and heterodinuclear (Ti/Zr) complexes were activated with [Ph3C][B(C6F5)4], B(C6F5)3, and a mixture of B(C6F5)3 with excess Et3SiH (SiHB system) as aluminium-free activators and tested in ethylene polymerization. Depending on the type of activator, unique reactivity was observed, resulting in either electron or methyl abstraction and the formation of cationic species. The catalytically active species are proposed to have dinuclear character, forming linear polyethylenes with unsaturated groups predominantly on the Zr cationic center. In contrast, the Ti cationic center generated by a SiHB system only in dichloromethane produced silicon-terminated polyethylenes.