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 (MgCl) (TiCl) complexes. Altogether ca. 1000 complexes with ranging from 1 to 19 and from 1 to 13 were studied. In line with the previous literature, the results consistently show that adsorption of TiCl onto MgCl preferably leads to octahedral six-coordination for both Mg and Ti atoms. This can be achieved by mononuclear binding of TiCl and binuclear binding of TiCl on (110) and (104) surfaces of MgCl, respectively. The preferred octahedral six-coordination is also achieved by binding of TiCl 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 TiCl on MgCl.