INFLUENCE OF ROTATION BETWEEN AGOSTIC STRUCTURES ON ETHENE INTERACTION WITH A ZIRCONOCENE POLYMERIZATION SITE

Density-functional theory has been used to study the first few steps o f ethene polymerization with the single-site catalyst Cp(2)ZrCH(3)(+) (biscyclopentadienyl methyl zirconium cation). Insertion of the first monomer yields a gamma-agostic product Cp(2)ZrC(3)H(7)(+) which can tr ansform into a more stable beta-agostic conformation with an activatio n barrier of 11 kJ mol(-1). The interaction of the beta-agostic struct ure with a second monomer leads to chain termination (front-side attac k) or insertion (back-side attack) with barriers of about 35-40 kT mol (-1). A more likely step appears to be insertion directly into the gam ma-agostic Cp(2)ZrC(3)H(7)(+), to form the gamma-agostic product Cp(2) ZrC(5)H(11)(+) with a barrier of only 11 kJ mol(-1).