Redox-Initiated Reactivity of Dinuclear β‑Diketiminatoniobium Imido Complexes

High-valent dichloride
and dimethylniobium complexes 1 and 2 bearing tert-butylimido and N,N′-bis­(2,4,6-trimethylphenyl)-β-diketiminate (BDIAr) ligands were prepared. The dimethyl complex reacted with
dihydrogen to release methane and generate the hydride-bridged diniobium­(IV)
complex 3 in high yield. One-electron oxidation of 3 with silver salts resulted in the release of dihydrogen
and conversion to a mixed-valent NbIII–NbIV complex, 4, 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 3 and 4. Finally, one-electron reduction
of 4 resulted in conversion to the highly dissymmetric
NbV–NbV dimer 5 that formed
from the reductive C–N bond cleavage of one of the BDIAr supporting ligands.