DENSITY-FUNCTIONAL CALCULATIONS ON AGOSTIC ETHYL-TI(IV) COMPLEXES

First principles, density functional theory embodied in the DMol progr am has been applied to agostic ethyl-Ti-complexes, including the dmpe complex, [Ti(-CH2CH3)Cl-3(dmpe)], where dmpe=(Me(2)PCH(2))(2) and its model complex, [Ti(-CH2CH3)Cl-3(PH3)(2)]. The ethyl moiety of the comp lexes can adopt two limiting conformations, staggered and eclipsed. In the model complex, [Ti(-CH2CH3)Cl-3(PH3)(2)], both conformers are fou nd to form agostic structures upon geometry optimization subject to Cs symmetry constraint, with the agostic eclipsed structure being the lo wer in energy. Full geometry optimization of the dmpe complex, [Ti(-CH 2CH3)Cl-3(dmpe)], yields an agostic structure with geometrical feature s similar to those measured by single crystal X-ray analysis. It is sh own that the HOMO orbital contributes substantially to the agostic bon ding.