Molecular Rearrangements of a Low-Valent Niobium Amide:  Ligand C−H Bond Oxidative Addition and Reductive Elimination

Reaction of the dinuclear and divalent (TMEDA)2Nb2Cl5Li(TMEDA) with Ph2NK led to the formation of three different compounds. The first complex contains no amide ligands. It is a mixed-valence dinuclear and paramagnetic species with a typical face-sharing bioctahedral structure Cl2Nb2(μ-Cl)3(TMEDA)2 (1). The second complex, a trivalent and dinuclear {[(Ph2N)2Nb]2[μ-NPh(μ-η1:η2-C6H4)](μ-H)}{Li(TMEDA)2}·toluene (2) with one hydride and one cyclometalated aromatic ring, is the result of oxidative addition of the two metal centers to the C−H bond. In a subsequent reaction step, the oxidative addition is followed by reductive elimination to restore the C−H bond to form the neutral, dinuclear, and diamagnetic (Ph2N)2Nb{[μ-NPh(η6-C6H5)]2Nb}·ether (3) containing the two metals in formal oxidation states of +4 and 0. Ab initio and EHMO calculations have been carried out in an attempt to clarify the nature of the Nb−Nb interaction in the three complexes.