Density functional calculations on agostic ethyl-Ti (IV) complexes

Abstract

First principles, density functional theory embodied in the DMol program has been applied to agostic ethyl-Ti-complexes, including the dmpe complex, [Ti(-CH 2CH 3)C1 3(dmpe)], where dmpe=(Me 2PCH 2) 2 and its model complex, [Ti(−CH 2CH 3)Cl 3(PH 3) 2]. The ethyl moiety of the complexes can adopt two limiting conformations, staggered and eclipsed. In the model complex, [Ti(−CH 2CH 3)C1 3(PH 3) 2], both conformers are found to form agostic structures upon geometry optimization subject to Cs symmetry constraint, with the agostic eclipsed structure being the lower in energy. Full geometry optimization of the dmpe complex, [Ti(−CH 2CH 3)C1 3(dmpe)], yields an agostic structure with geometrical features similar to those measured by single crystal X-ray analysis. It is shown that the HOMO orbital contributes substantially to the agostic bonding.