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(NtBu)2(NHtBu)2 with the di-basic carborane acid nido-7,8-C2B9H13 generates the tungsten(VI) carborane complex, [W(NtBu)(NHtBu)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(NtBu)(NHtBu)(2,6-Me2C6H3O)(C2B9H11)] 2, and water gives the μ-oxo complex {[W(NtBu)(NHtBu)(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(NtBu)(NHtBu)Cl(C2B9H11)] 4. Insertion of acetonitrile into the tungsten amido bond, followed by proton transfer gives {W(NtBu)2[N(H)C(Me)NHtBu](C2B9H11)} 5, the N-tert-butyl acetamidine adduct of the unknown M(1σ2π)3 complex [W(NtBu)2(C2B9H11)]. A structural study by X-ray diffraction reveals that compound 5 contains one short linear (W–N 1.750(3) A; W–N–C 173.8(3)°) and one longer bent (1.795(3) A, 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.