SYNTHESES, STRUCTURES AND ELECTROCHEMICAL CHARACTERIZATION OF MIXED CYCLOPENTADIENYL DITHIOLENE COMPLEXES OF TI(IV)

Cp2Ti(dithiolene) complexes are prepared by reacting Cp2TiCl2 with var ious dithiolenes, such as dmit2- (1,3-dithiole-2-thione-4,5-dithiolate ) or dddt2- (5,6-dihydro-1,4-dithiine-2,3-dithiolate), and their X-ray crystal structures are reported. Cp2Ti(dmit) crystallizes in the mono clinic system, SG C2/c with a = 23.651(5), b = 10.168(2), c = 16.025(6 ) angstrom, beta = 129.51(2)-degrees, Z = 8. Cp2Ti(dddt) crystallizes in the monoclinic system, SG P2(1)/c with a = 12.597(2), b = 10.945(3) , c = 21.300(2) angstrom, beta = 94.38(1)-degrees, Z = 4, with two ind ependent molecules in the unit cell. In both compounds the TiS2C2 ring is folded along the S-S axis, by 47.4(3)-degrees in Cp2Ti(dmit) and b y 49.2(1) and 51.2(1)-degrees in CP2Ti(dddt). The dynamics of the liga nd folding were characterized by variable temperature H-1 NMR studies, which show a relationship between the coalescence temperature, the ac tivation energy DELTAG double dagger and the actual folding angle. Tre atment of Cp2TiCl2 with two dmit2- equivalents affords the CpTi(dmit)2 - anion, isolated as its n-Bu4N+ salt. It crystallizes in the triclini c system, space group P - 1 with a = 10.003(3), b = 10.329(4), c = 19. 154(3) angstrom, alpha, = 81.36(2), beta = 75.67(2), gamma = 67.73(2)- degrees, Z = 2. A rationale for the observed puckering of the dithiole ne ligands in both types of complexes is given by extended Huckel calc ulations. For every compound investigated by cyclic voltammetry, a rev ersible reduction wave attributable to the Ti(IV)-Ti(III) process was observed while the oxidation leads to an irreversible ligand-centered process.