Chelate ring folding in titanocene complexes with bidentate sulfur- and oxygen-containing ligands: A theoretical study

The characteristic folding of the chelate ring in mono- and binuclear titanocene complexes with dithiolene-like ligands is studied by means of density functional theory (DFT). The structures resulting from geometry optimization (42.3degrees folding for Cp2TiS2C2H2) reflect the experimental situation well (46.1degrees for this complex) and are in accordance with the specific orbital interactions known to be responsible for the stabilizing effect of the folding. The significantly different folding obtained for the complexes with sulfur and oxygen donor atoms is the subject of a qualitative molecular orbital analysis. The calculations show that the tendency to fold appears for only one of the two possible formal bonding situations of the systems under study, the one with a Ti(IV) center and a dianionic ligand in the mononuclear cases and a tetraanionic ligand in the binuclear ones. The conclusion is derived that the tendency to fold is principally determined by the formal bonding situation, but the amount of folding is dependent on the specific donor atoms, sulfur or oxygen.