N═N Bond Cleavage by Tantalum Hydride Complexes: Mechanistic Insights and Reactivity.

The reaction of [TaCpX] (Cp = η-CMe, η-CHSiMe, η-CHMe; X = Cl, Br) with SiHPh resulted in the formation of the dinuclear hydride tantalum(IV) compounds [(TaCpX)(μ-H)], structurally identified by single-crystal X-ray analyses. These species react with azobenzene to give the mononuclear imide complex [TaCpX(NPh)] along with the release of molecular hydrogen. Analogous reactions between the [{Ta(η-CMe)X}(μ-H)] derivatives and the cyclic diazo reagent benzo[]cinnoline afford the biphenyl-bridged (phenylimido)tantalum complexes [{Ta(η-CMe)X}(μ-NCHCHN)] along with the release of molecular hydrogen. When the compounds [(TaCpX)(μ-H)] (Cp = η-CHSiMe, η-CHMe; X = Cl, Br) were employed, we were able to trap the side-on-bound diazo derivatives [(TaCpX){μ-(η,η-NCHCHN)}] (Cp = η-CHSiMe, η-CHMe; X = Cl, Br) as intermediates in the N═N bond cleavage process. DFT calculations provide insights into the N═N cleavage mechanism, in which the ditantalum(IV) fragment can promote two-electron reductions of the N═N bond at two different metal-metal bond splitting stages.