Testing DFT ability to predict thestereoselectivity of group 4 metallocenes inpropylene polymerization

In this study we have tested the ability of a standard DFT computational protocol to reproduce the experimentally obtained stereoselectivity of 26 different C2-symmetric zirconocene catalysts active in propylene polymerization. The catalysts werechosen for their relevance in metallocene catalyzed polymerization of propylene. To this end, primary insertion of both si- andre-propylene enantiofaces into the Zr-CH2-CH(CH3)2 bond was considered to simulate the growing chains step. The energydifference between these two transition states, ΔEre-si, was taken as a measure of the stereoselectivity (pentad: mmmm%) ofdifferent catalysts. The results clearly indicated that there was a good agreement between ΔEre-si and the mmmm% values, sothat greater ΔEre-si could correspond to higher mmmm%. A model was ftted to the experimentally obtained mmmm% againsttheoretical ΔEre-si. The coeffcient of determination (R2) of the resultant plot was 0.9793, which indicated a good accuracy of themodel. Finally, to quantify the steric role of the studied ligands in the observed stereoselectivity, the analysis of the buried volume(VBur) and of the steric maps was performed for two representative complexes. The images revealed that a greater asymmetriclocalization of the %VBur around the metal center led to a higher mmmm% in the resultant polymer. Polyolefns J (2014) 1:139-146

کلیدواژه ها:

Metallocene catalysts ، DFT ، Molecular simulation ، Setereoselective polymerization ، Isotactic polypropylene