Redox-Initiated Reactivity of Dinuclear β‑Diketiminatoniobium Imido Complexes

High-valent dichloride and dimethylniobium complexes <b>1</b> and <b>2</b> bearing <i>tert</i>-butylimido and <i>N</i>,<i>N</i>′-bis­(2,4,6-trimethylphenyl)-β-diketiminate (BDI^Ar) ligands were prepared. The dimethyl complex reacted with dihydrogen to release methane and generate the hydride-bridged diniobium­(IV) complex <b>3</b> in high yield. One-electron oxidation of <b>3</b> with silver salts resulted in the release of dihydrogen and conversion to a mixed-valent Nb^III–Nb^IV complex, <b>4</b>, that displayed a frozen-solution X-band electron paramagnetic resonance signal consistent with a slight dissymmetry between the two Nb centers. Spectroscopic and computational analysis supported the presence of Nb–Nb σ-bonding interactions in both <b>3</b> and <b>4</b>. Finally, one-electron reduction of <b>4</b> resulted in conversion to the highly dissymmetric Nb^V–Nb^V dimer <b>5</b> that formed from the reductive C–N bond cleavage of one of the BDI^Ar supporting ligands