Potential Catalyst Deactivation Reaction in Homogeneous Ziegler−Natta Polymerization of Olefins: Formation of an Allyl Intermediate

Abstract

We investigate the possibility of premature deactivation of d0 transition metal Ziegler−Natta metallocene catalysts Cp‘2MR+ (Cp‘ = any cyclopentadienyl derivative) used in homogeneous olefin polymerization. Density functional calculations show that β-hydride elimination from the β-agostic precursor likely leads to formation of an allyl dihydrogen complex. This complex is prone to eject the dihydrogen ligand and form a “torpid” Cp‘2M (allyl)+ complex that can be slow to restart chain propagation, depending on the steric hindrance imposed on the metal by the Cp‘ moiety. Our theoretical observations are in line with previous experimental evidence for such a reaction.