Adsorption of Titanium Tetrachloride on Magnesium Dichloride Clusters

Magnesium dichloride and titanium tetrachloride are key components in heterogeneous Ziegler-Natta olefin polymerization catalysis. We have determined the preferred binding modes of titanium tetrachloride on magnesium dichloride clusters at the M06-2X level of theory, thus accounting for dispersion. A systematic study was carried out to locate the lowest energy isomers of (MgCl₂) (TiCl₄) complexes. Altogether ca. 1000 complexes with n ranging from 1 to 19 and m from 1 to 13 were studied. In line with the previous literature, the results consistently show that adsorption of TiCl₄ onto MgCl₂ preferably leads to octahedral six-coordination for both Mg and Ti atoms. This can be achieved by mononuclear binding of TiCl₄ and binuclear binding of Ti₂Cl₈ on (110) and (104) surfaces of MgCl₂, respectively. The preferred octahedral six-coordination is also achieved by binding of TiCl₄ on defect sites, of which the most striking example is trinuclear binding mode at corners of the clusters. Overall, the results highlight the relevance of multinuclear binding of TiCl₄ on MgCl₂.