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) 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.