REACTIONS OF DINUCLEAR AND POLYNUCLEAR COMPLEXES .13. SYNTHESIS, STRUCTURE AND FLUXIONAL BEHAVIOR OF HYDRIDO-BRIDGED THIOLATO-BRIDGED OR SELENATO-BRIDGED COMPLEXES [MO(2)CP(2)(MU-H)(MU-ER)(CO)(4)] (E=S, R=ME, (T)BU, BZ, OR PH E=SE, R=PH)

Oxidative addition of thiols or selenoles across the Mo-2 centre of [M o(2)Cp(2)(CO)(4)] gives complexes with bridging thiolate or selenate a nd hydride ligands [Mo(2)Cp(2)(mu-H)(mu-ER)(CO)(4)] (E = S, R = Me (4) , (t)Bu (5), Bz (6), Ph (7); E = Se, R = Ph (8)). The complex 4 is als o formed on reaction of [Mo(2)Cp(2)(mu-SMe)(2)(CO)(4)] with vanadocene [VCp(2)] with the possible involvement of a thioaldehyde, hydride der ivative of the vanadocene. Crystals of 4 are monoclinic, space group C 2/c, with a = 17.225 (1), b = 8.418 (1) c = 22.960 (2) Angstrom, beta= 90.346 (5)degrees, R = 0.023 for 4213 observed reflections. In the sol id state, molecules of 4 contain a planar MO(2)(mu-H)(mu-S) core and t he Cp ligands are cis with respect to the Mo-Mo bond, the two CpMo(CO) (2) units being related by an approximate plane of symmetry which cont ains the bridging H and S donor atoms and which is normal to the Mo-Mo bond. The fluxional nature of complexes 4-8 in solution is shown from variable-temperature H-1 and C-13 NMR spectra to arise from cis-trans isomerisation.