POLYNUCLEAR METAL HYDRIDE ALKOXIDES .2. HYDROGENATION OF 1,2-W-2(BU-I)(2)((OPR)-PR-I)(4) - PREPARATION, CHARACTERIZATION, AND SOME REACTIONS OF W6H5((CPR)-PR-I)((OPR)-PR-I)(12) - W-2(H)(2)((OPR)-PR-I)(4)(DMPE)(2), AND W-4(H)(4)(DMPM)(3), WHERE DMPE EQUALS BIS(DIMETHYLPHOSPHINO)ETHANE AND DMPM EQUALS BIS(DIMETHYLPHOSPHINO)METHANE

H-2 and 1,2-W-2(Bu-i)(2)((OPr)-Pr-i)(4) react in hydrocarbon solvents to give the cluster W-6(H)(5)((CPr)-Pr-i)((OPr)-Pr-i)(12) (1) in 40% c rystalline yield. W-2(H)(2)((OPr)-Pr-i)(4)(dmpe)(2) (2) and W-4(H)(4)( (OPr)-Pr-i)(8)(dmpm)(3) (3) have been isolated in the presence of the chelating diphosphines Me2PCH2CH2PMe2 (dmpe) and Me2PCH2PMe2 (dmpm). R eactions involving the use of various isotopes reveal the importance o f both alpha- and beta-CH activation of the Bu-i ligand. An X-ray dete rmination and NMR data reveal that 1 contains an octahedral W-6 unit, W-W = 2.58 to 2.85 Angstrom, supported by four bridging hydride ligand s, seven bridging alkoxides, and one bridging isobutylidyne ligand in addition to five terminal (OPr)-Pr-i and one terminal hydride: )(mu-(C Pr)-Pr-i)(mu-(OPr)-Pr-i)(7)((OPr)-Pr-i)(5). Only one isomer is observe d crystallographically, and the NMR data are indicative of its presenc e in solution. The cluster 1 is inert with respect to intramolecular l igand site exchange, which has allowed the detection of preferential h ydrogenolysis and hydrogenation involving the terminal W-H ligand whil e alcoholysis occurs preferentially at the terminal W-(OPr)-Pr-i site adjacent to three mu-H ligands. In the solid state, compound 2 has fou r terminal (OPr)-Pr-i ligands on one W atom and two dmpe ligands on th e other: ((PrO)-Pr-i)(4)W(mu-H)(2)W(dmpe)(2), W-W = 2.49 Angstrom. The locations of the two mu-H ligands are inferred from the X-ray determi nation and their proposed locations are consistent with the hydride-lo cating program XHYDEX. In solution, 2 is fluxional and low-temperature H-1 and P-31{H-1) NMR spectra are consistent with the presence of two isomers, one of which is the same as that seen in the solid state whi le the other has the more symmetrical disposition of ligands e)((PrO)- Pr-i)(2)W(mu-H)(2)W((OPr)-Pr-i)(2)(dmpe). Compound 3 contains a chain of four tungsten atoms with terminal W-W distances of similar to 2.5 A ngstrom and a central W to W distance of 3.6 Angstrom, bridged by thre e dmpm ligands. The solid-state molecular structure is proposed as mu- (OPr)-Pr-i)W(mu-dmpm)(3)(mu-H)W((OPr)-Pr-i)(4). The solution NMR data reveal that 3 is fluxional but that at low temperatures a structure ak in to that formulated above is present. These results are discussed in terms of the developing chemistry of hydride alkoxides of the early t ransition elements.