Preparation and Reactions of Molybdenum and Tungsten Hydride Complexes Containing the Tetraphosphane Ligand meso-o-C6H4(PPhCH2CH2PPh2)(2)

The reaction of [Mo(kappa(2)-dppe)(kappa(4)-P4)] (1a) {dppe = PPh2CH2CH2PPh2, P4 = meso-o-C6H4(PPhCH2CH2PPh2)(2)} with 1 atm of H-2 at room temperature selectively gave [MoH2(kappa(2)-dppe)(kappa(3)-P4)] (3a). The W analogue of 1a reacted with 1 atm of H-2 at 80 degrees C to form a mixture of [WH2(kappa(2)-dppe)(kappa(3)-P4)] and [WH4(kappa(4)-P4)] (5b), the latter of which could be cleanly prepared by the reduction of [WBr2(kappa(4)-P4)] with NaBH4 in ethanol at 50 degrees C. The molecular structure of complex 5b differed from that of the related complex [WH4( dppe)(2)] and showed much higher reactivity. Insertion into the W-H bonds took place in the reaction of 5b with CS2 at 50 degrees C to give the methylenedithiolate complex [W(kappa(2)-S2CH2)(kappa(4)-P4)] (6) as the sole product, and the hydride ligands in 5b were replaced by isocyanides at 80 degrees C to form [W(CNR)(2)(kappa(4)-P4)] {R = tBu (7), 2,6-Me2C6H3 (8)} in moderate yields. The detailed structures were determined by X-ray crystallography for 3a, 5b, 6, and 7, while the fluxional behavior of 3a in solution was clarified by variable-temperature NMR (VT NMR) spectroscopic studies.