A Novel Class of Hexanuclear Titanoxanes: Synthesis, Structure and Electronic Configuration

Reduction of cyclopentadienyloxochloro complexes such as [R-cpTiCl(mu(2)-O)](4) (R = H (1), Me (2) or SiMe(3) (3)) with a variety of reducing agents (Zn, Na, Mg or LiN3) in tetrahydroforum gave the hexanuclear titanoxanes [(R-cp)(6)Ti6O6Cl(2)] (R = H (4), Me (5) or SiMe(3) (6)) with a good yield. Complexes 4-6 are soluble in organic solvents, are diamagnetic and contain four electrons more than are required for the existence of the hexanuclear skeleton. Complex 4 was equally satisfactorily obtained by reducing [R-cpTiCl(2)(mu(2)-O)] (R = H) (7) will Bu(3)SnH. Reduction of 1 and 2 with Al powder gave [R-cp(6)Ti(6)O(4)Cl(4)] (R = 1-1 (8) or Me (9)). They contain two unpaired electrons. Reaction of H2O with 4 and 5 gave the diamagnetic titanoxane [R-cp(6)Ti(6)O(8)] (R = H (11) or Me (12)). Complexes 4-6, 8, 9, 11 and 12 all contain an octahedron of titanium atoms faced by triply bridging oxygen and chlorine in the reported ratio. Molecular orbital calculations showed that a band of 12 non-bonding orbitals may accommodate electrons in excess of those needed for the existence of the Ti-6 skeleton and so the systems can be used in their intact form for storing and releasing electrons. The structures of complexes 4, 6, 9 and 12 were determined by single-crystal X-ray diffraction studies.