THEORETICAL-STUDY ON HYDROZIRCONATION

An ab initio MO study has been carried out for hydrozirconation of ethylene and acetylene by Cp2Zr(H)Cl. Of the two possible reaction paths, attack of ethylene and Acetylene at Zr between the Cl and H ligands (path 1) and that from the opposite side of the Cl ligand (path 2), the former is found to be more favorable, with a very low activation energy. With an energy decomposition analysis, this difference has been attributed to the smaller distortion of the Zr complex required to reach the transition state for path 1. Hydrozirconation of acetylene is intrinsically more difficult than that of ethylene. The olefin insertion at Cp2Zr(R)Cl, R = alkyl, i.e. the second insertion of olefin, is substantially more difficult than hydrozirconation (R = H) the first insertion. Its origin is also discussed. For comparison, the results of hydrozirconation by Cl3ZrH have been presented, to clarify the size effect of Cp ligand.