Polynuclear Metal Hydrido Alkoxides. 2. Hydrogenation of 1,2-W₂(ⁱBu)₂(OⁱPr)₄. Preparation, Characterization, and Some Reactions of W₆H₅(CⁱPr)(OⁱPr)₁₂, W₂(H)₂(OⁱPr)₄(dmpe)₂, and W₄(H)₄(dmpm)₃, Where dmpe = Bis(dimethylphosphino)ethane and dmpm = Bis(dimethylphosphino)methane

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.

Consecutive fragmentations of the cubane-like zinc cluster [CH3Zn(O-i-C3H7)]4upon electron ionization

“…In marked contrast, elimination of CH 3 ZnO-i-C 3 H 7 is almost negligible for the trinuclear zinc cluster [(CH 3 ) 2 Zn 3 (O-i-C 3 H 7 ) 3 ] 1 (m/z ¼ 399 for the 64 Zn 3 isotope) whose fragmentation occurs in two different ways. The predominating route leads to loss of neutral acetone, (CH 3 ) 2 CO, concomitant with an ionic fragment to which we tentatively assign the structure of a hydrido-metal alkoxide, 32 i.e., 2). A minor, but yet notable route involves the elimination of a neutral entity with Dm ¼ À80 for 64 Zn; corresponding mass shifts are observed for ions containing other zinc isotopes.…”

Linking Multiple Bonds between Metal Atoms: Clusters, Dimers of “Dimers”, and Higher Ordered Assemblies

“…Two other clusters derived from (M⋮M) 6+ centers warrant mention. The hydrogenation of W 2 ( i Bu) 2 (O i Pr) 4 in hydrocarbon solvents leads to a most unusual cluster hydride: W 6 (H) 5 (C i Pr)(O i Pr) 12 . This compound was originally formulated as W 6 (H) 5 (O i Pr) 13 , but a more carefully crystallographic refinement and a detailed 13 C [ 1 H] study revealed the presence of the μ-C i Pr ligand.…”

Zirconium Hydride Complex Supported by a Tetradentate Carbon-Centered Tripodal Tris(aryloxide) Ligand: Synthesis, Structure, and Reactivity

“…Therefore, the design of auxiliary ligand systems provides an attractive avenue to explore hydride complexes with novel properties. For early transition metals, hydride species have played a crucial role in studying olefin hydrogenation, polymerization, and CO reduction. , While most of them contain the cyclopentadienyl ligand and its substituted derivatives, there is a highly reactive class of compounds incorporating O-donor ligands such as alkoxide, aryloxide, or siloxide ligands due to their coordinative unsaturation. Rothwell and co-workers reported that niobium and tantalum hydride species supported by bulky aryloxide ligands were implicated in catalytic hydrogenation of polycyclic aromatic hydrocarbons with good chemoselectivity and stereoselectivity .…”