Comparing families of olefin polymerization precatalysts using the percentage of buried volume

We report a systematic comparison of the steric properties of different stereoselective olefin polymerization catalysts using the percentage of buried volume, %V_Bur, as a molecular descriptor. For the first time, isoselective and syndioselective group 4 metallocenes are compared with group 4 isoselective phenoxy-amine and group 4 syndioselective phenoxy-imine catalysts using the same molecular descriptor. The results indicate that the basic bis-Cp skeleton of metallocenes is more hindered than the unsusbtituted skeleton of phenoxy-amine and phenoxy-imine based catalysts. The different effect of the same alkyl substituents on the different catalysts skeleton is also examined. A reasonable correlation is found between the experimental stereoselectivity and the %V_Bur.