Reduction of (tBuN)NbCl3(py)2 in a Salt-Free Manner for Generating Nb(IV) Dinuclear Complexes and Their Reactivity toward Benzo[c]cinnoline

The organosilicon reducing reagent 2,3,5,6-tetramethyl-1,4-bis­(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (1a) was used for the one-electron, salt-free reduction of (tBuN)­NbCl3(py)2 (2), resulting in the formation of a neutral, triply chloride-bridged dinuclear niobium­(IV) complex, [(tBuN)­ClNb­(py)]­(μ-Cl)3[(tBuN)­Nb­(py)2] (3) in moderately high yield. Heating 3 in toluene at 80 °C caused a unique intramolecular rearrangement of 3 to another neutral dinuclear complex, [Cl2Nb­(py)]­(μ-Cl)­(μ-NtBu)2[ClNb­(py)2] (4), in which two niobium­(IV) atoms were bridged by one chloride atom and two imido ligands. Reaction of complex 3 with benzo­[c]­cinnoline produced a benzo­[c]­cinnoline-bridged dinuclear niobium­(V) complex 7 by an overall two-electron reduction of benzo­[c]­cinnoline through a disproportionation of 3 into a mixture of a niobium­(V) complex 2 and a niobium­(III) complex, the latter of which efficiently reduced benzo­[c]­cinnoline.