Theoretical study of ethylene polymerization on Ziegler-Natta catalysts and on metallocene catalysts

Ethylene insertion on O-h-d(1)CH(3)Ti(n) chloride clusters/C2H4 (model syst ems of Ziegler-Natra catalysts) and T-d-d(0)-d(1)CH(3)TiCp(2)/C2H4 (model s ystems of metallocene catalysts) were studied by using paired interacting o rbitals (PIO) analysis and LFO calculation. Electron delocalization from ca talytic site to ethylene and that from ethylene to catalytic site played a crucial role in ethylene insertion. The former depends on the nucleophilici ty of the active site and the latter on the electrophilicity of the active site. They were quantitatively estimated by LFO calculation. In the case of O-h systems, the electrophilicity of the catalyst decreased because of the Cl anion located trans to the ethylene in the reaction plane. In the case of Td systems, since the electrophilicity was not weakened because of the a bsence of the trans ligand to the ethylene, the nucleophilicity and electro philicity were well balanced. The O-h-d(1)Ti(4) cluster could be a suitable model of the active site on the TiCl3 crystalline surface. (C) 1999 Elsevi er Science B.V. All rights reserved.