Molecular structure of 2,2'-thiobis(4-methyl-6-tert-butylphenoxy) titanium diisopropoxy. Influence of titanium-sulfur interaction on coordination geometry

The molecular structure of 2,2′-thiobis(4-methyl-6-tert-butylphenoxy) titanium diisopropoxy (1a) has been determined. The molecule exists as a dimer, in which the 1,3-dioxadititanacycle is supported by two bridging iPrO ligands. The coordination environment about each Ti center is best described as a distorted octahedron, where the S atom and one iPrO ligand occupy the axial positions, whilst two terminal phenolate and two bridging iPrO ligands occupy the equatorial sites. The eight-membered dioxatitanacycle adopts a symmetric-syn boat conformation, which allows for a significant sulfur-titanium interaction S-Ti distance 2.724(2) Å). A comparison between these structural features and those reported for the monomeric tetrahedral complexes 2b and 2d, where the sulfur atom is replaced by a methylene bridge in the bisphenoxy ligand, highlights the influence of the S-Ti interaction on coordination geometry. The structural features suggested for 1a to account for the higher catalytic activity of 1a/MAO in polymerization of α-olefins as compared with 2a/MAO are clearly demonstrated.