Tungsten(VI) metallacarborane imido complexes; hydrogen bonding to a bent imido ligand in {W(NtBu)2[N(H)C(Me)NHtBu](C2B9H11)}

Abstract

The amine elimination reaction of W(N^tBu)₂(NH^tBu)₂ with the di-basic carborane acid nido-7,8-C₂B₉H₁₃ generates the tungsten(VI) carborane complex, [W(N^tBu)(NH^tBu)₂(C₂B₉H₁₁)] 1, in which a C₂B₉H₁₁ ligand has replaced one imido ligand. One of the remaining amido ligands can be substituted by acidic functions, thus 2,6-dimethylphenol yields [W(N^tBu)(NH^tBu)(2,6-Me₂C₆H₃O)(C₂B₉H₁₁)] 2, and water gives the μ-oxo complex {[W(N^tBu)(NH^tBu)(C₂B₉H₁₁)]₂(μ-O)} 3 as a mixture of racemic and meso diastereomers. Complexes 1 and 2 have been characterised by single crystal X-ray diffraction, revealing that replacing an amido ligand in 1 by a weaker π-donor phenoxide in 2 results in shorter metal–amido and metal–dicarbollide distances. Substitution of one amido ligand in 1 by a chloro ligand is achieved using Me₃SiCl giving [W(N^tBu)(NH^tBu)Cl(C₂B₉H₁₁)] 4. Insertion of acetonitrile into the tungsten amido bond, followed by proton transfer gives {W(N^tBu)₂[N(H)C(Me)NH^tBu](C₂B₉H₁₁)} 5, the N-tert-butyl acetamidine adduct of the unknown M(1σ2π)₃ complex [W(N^tBu)₂(C₂B₉H₁₁)]. A structural study by X-ray diffraction reveals that compound 5 contains one short linear (W–N 1.750(3) Å; W–N–C 173.8(3)°) and one longer bent (1.795(3) Å, 151.4(3)°) imido ligand, with a hydrogen bond between the amidine and bent imido ligand, demonstrating for the first time that a sp² hybridised bent imido ligand can act as a hydrogen bond acceptor.