Regioselective homo- and codimerization of alpha-olefins catalyzed by bis(2,4,7-trimethylindenyl)yttrium hydride

Over the past decade, metallocene-based olefin polymerization catalysts have become important single-site alternatives to the heterogeneous Ziegler-Natta systems. Two types of 14-electron metallocene systems can be distinguished: cationic group 4 metal complexes of the type [Cp2MR] + 1a,c-f,2 and neutral group 3 metal or lanthanide complexes Cp2LnR. 1a,3,4 The latter are extremely efficient catalysts for the polymerization of ethene, but in contrast to the cationic group 4 congeners, they are largely ineffective for the polymerization of α-olefins (mainly due to deactivation through allylic C-H activation of the substrate). Only the recently developed ansa-metallocenes of the group 3 metal yttrium, such as Me2Si[C5(SiMe3)(CMe3)H2]2YR, give slow formation of polymers of α-olefins in moderate yield. Here we describe the synthesis of the first alkyl and hydride compounds of a bis(indenyl)yttrium system, with 2,4,7-trimethylindenyl as ancillary ligand. Again,