Bis[2-(tert-butyldimethylsiloxy)-4,7-dimethylindenyl]zirconium dichloride, synthesis, torsional isomerism and olefin polymerization catalysis

The synthesis and characterization of an unbridged metallocene catalyst precursor bis[2-(tert-butyldimethylsiloxy)-4:7-dimethylindenyl]zirconium dichloride (3) is reported. The solid state structure of 3 reveals two different rotamers in the asymmetric unit corresponding to a C-1 symmetric, 'central/lateral:gauche'-like conformation, and a C-2 symmetric, 'central:syn' conformation, respectively. The H-1 and C-13 NMR spectra of 3 are, at ambient temperature, consistent with time-averaged molecular C-2v symmetry. Dynamic NMR measurements show splitting of the H-1 resonances at 173 K indicating that a single C-2 symmetric bent-metallocene conformation is observed. Upon activation with methylaluminoxane, 3 polymerizes ethylene with an activity of 500 kg PE/mol Zr/h (T-p = 80 degrees C; P(C2H4) = 1.6 bar; [Al]:[Zr] = 3000:1; M-w = 43000; M-w/M-n = 2.2; T-m = 133 degrees C). (C) 1998 Elsevier Science S.A. All rights reserved.