Reaction of (bisimido)niobium(V) complexes with organic azides: [3 + 2] cycloaddition and reversible cleavage of ß-diketiminato ligands involving nitrene transfer.

We describe the unusual reactivity of a highly labile diethyl ether adduct of an asymmetric niobium(V) bis(imide) 2.OEt2 containing the monoazabutadiene (MAD) ligand. This species undergoes clean nitrene transfer on treatment with tert-butyl- or di-isopropylphenyl azide resulting in the unprecedented reformation of nacnac ligands bound to the metal center. Corresponding reactions with trimethylsilyl- or tert-butyl azide allowed the isolation of two rare intermediates prior to N2 loss; mechanistic studies support the involvement of two different niobium species.