Reactions of [W2(OCH2tBu)8] (MM) with diazobenzene and trimethylsilyldiazomethane. Preparation and structures of W2(OCH2tBu)8(NPh) and W2(OCH2tBu)8(N2C(H)SiMe3)

Abstract

Hydrocarbon solutions of W₂(OCH₂^tBu)₈ (MM) react with azobenzene at room temperature to give the phenylimido-bridged compound W₂(μ-NPh)(μ-OCH₂^tBu)₂(OCH₂^tBu)₆ which has a confacial biooctahedral geometry with a W–W single bond length of 2.5613(2) Å and W–N = 1.987(3) Å (ave). Similarly, W₂(OCH₂^tBu)₈ (MM) and trimethylsilyldiazomethane react to give the 1 ∶ 1 adduct W₂(μ-N₂C(H)SiMe₃)(μ-OCH₂^tBu)₂(OCH₂^tBu)₆ which has a W–W distance of 2.5626(2) Å and W–N = 1.985(1) Å (ave). The μ-N₂CHSiMe₃ ligand can be described as a hydrazonido(2−) ligand. The N–N distance is 1.366(4) Å and the N–N–C angle is 120.1(3)°. The NNC plane of the bridging ligand is perpendicular to the W–W bond axis. The bonding in these molecules is discussed in the light of electronic structure calculations employing density functional theory. The present findings are contrasted with related reactions involving MM multiply bonded compounds and with low valent early transition metal complexes that are similarly known to activate N–N bonds.