(dme)MCl₃(NNPh₂) (dme = dimethoxyethane; M = Nb, Ta): A Versatile Synthon for [TaNNPh₂] Hydrazido(2-) Complexes

Complexes (dme)TaCl3(NNPh2) (1) and (dme)NbCl3(NNPh2) (2) (dme =1,2-dimethoxyethane) were synthesized from MCl5 and diphenylhydrazine via a Lewis-acid assisted dehydrohalogenation reaction. Monomeric 1 has been characterized by X-ray, IR, UV−vis, 1H NMR, and 13C NMR spectroscopy and contains a κ1-bound hydrazido(2-) moiety. Unlike the corresponding imido derivatives, 1 is dark blue because of an LMCT that has been lowered in energy as a result of an Nα−Nβ antibonding interaction that raises the highest occupied molecular orbital (HOMO). Reaction of 1 with a variety of neutral, mono- and dianionic ligands generates the corresponding ligated complexes retaining the κ1-bound [Ta−NNPh2] moiety.