Synthetic explorations towards sterically crowded 1,2,3-substituted bis(indenyl)zirconium(IV) dichlorides

The systematic synthesis of 1,3-dialkyl-substituted 2-silylindenes and their suitability as zirconocene ligands is discussed. Unexpected reactivities rendered a number of substitution patterns unfeasible, especially for alkyl groups other than methyl in 2-(trimethylsilyl)indene derivatives, and essentially for all derivatives of 2-(dimethylsilyl)indene. The syntheses of rac/meso-bis[1-methyl-2-(trimethylsilyl)indenyllzirconium(IV) dichloride (12) and bis[1,3-dimethyl-2-(trimethylsilyl)indenyllzirconium(IV) dichloride (13b) are described. The solid-state structure of the latter displays strong deformations within the ligand framework and an unusually large Cp-centroid-Zr-Cp-centroid angle. Both, 12/MAO and 13b/ MAO, displayed ethene and ethene-co-1-hexene polymerization activity. Curiously, 13b/MAO shows an extraordinary monomer selectivity, which can be rationalized by means of DFT calculations on the active site. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).