Reaction of (Bisimido)niobium(V) Complexes with Organic Azides: [3 + 2] Cycloaddition and Reversible Cleavage of β‑Diketiminato Ligands Involving Nitrene Transfer

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