Preparation of monomethyl-niobium(V) and -tantalum(V) halides and of some of their complexes

Abstract

Monoalkylated compounds MeNbCl₄, MeTaCl₄, and MeNbBr₄ have been synthesized by treating the corresponding metal(V) halides with either HgMe₂ or SnMe₄. With the chlorides the reactions were rapid and simple: only the monoalkyl derivatives were formed and isolated in quantitative yields, along with either HgCl₂ or ClSnMe₃. No further substitution was observed in the presence of an excess of either of the alkylating agents. The reaction of HgMe₂ with NbBr₅ was much slower and MeHgBr was formed. The reaction of SnMe₄ with NbBr₅ does not go to completion. The new compounds have been characterized by elemental analysis, cryoscopic molecular-weight determinations, n.m.r. and i.r. spectroscopy, mass spectrometry, and by the identification of a range of adducts, several of which were isolated, i.e.[MeNbCl₄],L (L = PPh₃, Ph₂PCH₂CH₂PPh₂, or γ-picoline) and [MeNbBr₄], L (L = Ph₂PCH₂CH₂PPh₂ or 2,2′-bipyridine).