Effect of Ligand Structure on Olefin Polymerization by a Metallocene/Borate Catalyst: A Computational Study

We have carried out a systematic computational study on olefin polymerization by metallocene/borate catalysts, using three metallocenes: Cp 2 ZrMe 2 ( Cp ), rac -SiMe 2 -bis(1-(2-Me-(4-PhInd))ZrMe 2 ( 4-PhInd ), and rac -SiMe 2 -bis(1-(2-Me-(4,5-BenzInd))ZrMe 2 ( 4,5-BenzInd ). Detailed reaction pathways, including the structure of the catalytically active ion pair, anion displacement, chain propagation, and chain termination steps, are reported for ethene homopolymerization, alongside with investigation of ethene–propene copolymerization reactions. Initially, all catalysts form inner-sphere ion pairs ([L 2 ZrMe] + –[B(C 6 F 5 ) 4 ] − ) with a direct Zr–F interaction, which is weak enough to be displaced by the incoming monomer. In comparison to Cp, the bulky and electron-rich 4-PhInd and 4,5-BenzInd show higher barriers for anion displacement but lead to relative stabilization of the resulting π complexes. 4-PhInd enables the most feasible propene uptake, and both catalysts suppress the chain termination reactions relative to Cp . The borate counterion is shown to have a minor influence after the catalyst activation step.