Structure-property relationships of zirconocene catalysts in propylene polymerization

Abstract

In this study, the quantum chemical calculations were performed onfive zirconocene structures in which geometries were optimized at variouslevels of theory such as B3LYP/DZVP, B3LYP/LANL2DZ, and ONIOM (B3LYP/DZVP :UFF). All optimized parameters of various methods were compared. Structuralparameters such as distance between Cp planes, angle between Cp planes, gapaperture, obliquity, twisted angle, cavity distance, and cavity angle wereelucidated from these optimized geometries to seek for relations withcatalytic properties such as % isotacticity and productivity. From theplots between catalytic properties and structural parameters, the distanceand angle between Cp planes increase as the % isotacticity increase, whichcould be used to design new catalysts with higher selectivity. Forreactivity, the productivity increases as the gap aperture, cavitydistance, and cavity angle increases. Also Zr charges as well as charges onthe cyclopentadienyl rings, in the ion form gives good relation with theexperimental productivity. Thus, the steric at transition state whichrepresented by large cavity (distance between Cp planes) controls theselectivity and the rate of entering cavity which represented by theentrance channel (cavity distance) and the electronic effect ofsubstituents represented by charge on zirconium controlled the reactivity.This knowledge was used to suggest new zirconocene catalyst with requiredcatalytic properties