A DFT study on the effect of hydrogen in ethylene and propylene polymerization using a Ti-based heterogeneous Ziegler-Natta catalyst

Hydrogenolysis of a series of model Ziegler-Natta (Z-N) catalysts to form Ti-H bond was studied within DFT. We focused our efforts on Ti species attached to the (110) lateral cut of MgCl2 which exist as different centres including Ti-C2H5, Ti-CH2CH(CH3)(2), and Ti-CH(CH3)CH2CH3 in ethylene and propylene polymerization. In the next step, reactivity of Ti H bond towards ethylene and propylene (1,2- and 2,1-) insertion was investigated. Results showed that insertion of ethylene and propylene into Ti H bond has less barrier, in comparison with their insertion in Ti-C bond, however, ethylene and propylene 2,1-insertion lead to Ti-C2H5 and Ti-CH(CH3)(2) centres respectively, which were stable due to strong 1 beta-agostic interactions. Finally, by considering different possible reactions of active centre, activity depression in ethylene polymerization and activity increase in propylene polymerization were explained in detail. (C) 2012 Elsevier B.V. All rights reserved.