No abstract

No abstract

H2 and 1,2-W2(iBu)2(OiPr)4 react in hydrocarbon solvents to give the cluster W6(H)5(CiPr)(OiPr)12 (1) in 40% crystalline yield. W2(H)2(OiPr)4(dmpe)2 (2) and W4(H)4(OiPr)8(dmpm)3 (3) have been isolated in the presence of the chelating diphosphines Me2PCH2CH2PMe2 (dmpe) and Me2PCH2PMe2 (dmpm). Reactions involving the use of various isotopes reveal the importance of both α- and β-CH activation of the iBu ligand. An X-ray determination and NMR data reveal that 1 contains an octahedral W6 unit, W−W = 2.58 to 2.85 Å, supported by four bridging hydride ligands, seven bridging alkoxides, and one bridging isobutylidyne ligand in addition to five terminal OiPr and one terminal hydride:  W6(H)(μ-H)4(μ-CiPr)(μ-OiPr)7(OiPr)5. Only one isomer is observed crystallographically, and the NMR data are indicative of its presence in solution. The cluster 1 is inert with respect to intramolecular ligand site exchange, which has allowed the detection of preferential hydrogenolysis and hydrogenation involving the terminal W−H ligand while alcoholysis occurs preferentially at the terminal W−OiPr site adjacent to three μ-H ligands. In the solid state, compound 2 has four terminal OiPr ligands on one W atom and two dmpe ligands on the other:  (iPrO)4W(μ-H)2W(dmpe)2, W−W = 2.49 Å. The locations of the two μ-H ligands are inferred from the X-ray determination and their proposed locations are consistent with the hydride-locating program XHYDEX. In solution, 2 is fluxional and low-temperature 1H and 31P{1H} NMR spectra are consistent with the presence of two isomers, one of which is the same as that seen in the solid state while the other has the more symmetrical disposition of ligands (dmpe)(iPrO)2W(μ-H)2W(OiPr)2(dmpe). Compound 3 contains a chain of four tungsten atoms with terminal W−W distances of ∼2.5 Å and a central W to W distance of 3.6 Å, bridged by three dmpm ligands. The solid-state molecular structure is proposed as (iPrO)3W(μ-H)(μ-OiPr)W(μ-dmpm)3(μ-H)W(μ-H)2W(OiPr)4. The solution NMR data reveal that 3 is fluxional but that at low temperatures a structure akin to that formulated above is present. These results are discussed in terms of the developing chemistry of hydrido alkoxides of the early transition elements.

No abstract