Catalytic reactions on magnesium dichloride clusters saturated by titanium tetrachloride

Abstract Magnesium dichloride, titanium tetrachloride, and triethyl aluminum are essential components in the Ziegler-Natta catalysts for olefin polymerization. We report a systematic computational investigation (M06-2X/def-TZVP level of theory, thus accounting for dispersion) of the thermodynamics of a sequence of catalytic reactions leading to ethylene polymerization in the absence of electron donors. The reactions are explored for a series of TiCl4-adsorbed magnesium dichloride clusters as a function of the adsorption site, involving (104)- and (110)-type ideal edge sites alongside with corners representing defect sites. The reactions comprise alkylation of TiCl4, reduction from Ti(IV) to Ti(III) and Ti(II), ethylene π-complexation to Ti(III), and chain growth. The polymerization process as a whole is shown to be strongly exergonic for all adsorption sites, with coordination numbers of the site mainly contributing to the reduction and π-complexation energies.