A second transition state for chain transfer to monomer in olefin polymerization promoted by group 4 metal catalysts.

beta-Hydrogen transfer (BHT) to monomer is the dominant chain termination pathway for olefin polymerization promoted by group 4 metal catalysts. The transition state (TSA) for BHT studied in earlier work is characterized by a strong metal-hydrogen interaction. Our theoretical study of a series of homogeneous single-site polymerization catalysts reveals the existence of a second transition state (TSC), competitive with TSA, which has no direct metal-hydrogen interaction and strongly resembles that for the main-group metal aluminum. The balance between the two reaction paths is sensitive to choice of metal and ligand structure.