The reactivity of niobium and tantalum pentahalides with imines

The reactivity of NbCl5, NbF5 and TaCl5 with a selection of commercial imines was investigated for the first time by using dichloromethane as reaction medium. NbCl5 reacted with Ph2CNH, in 1:2 molar ratio, affording [Ph2CNH2][NbCl5(NCPh2)], 1, in 55% yield, as result of imine self-protonation. The iminium salt [PhCHNHtBu][NbCl6], 2, was isolated in 52% yield from NbCl5 and PhCHNtBu (1:1 molar ratio), while a low yield of [tBu2CNH2][NbCl6], 3, was identified from NbCl5/tBu2CNH. The 1:1 reactions of NbF5 with Ph2CNH and PhCHNtBu were accompanied by electron interchange and led to the isolation of the salts [Ph2CNH2][NbF6], 4, and [PhCHNHtBu][NbF6], 5, respectively, in ca. 50% yields. Few crystals of [Ph2CNH2]2[Ta2Cl10O], 6, were recovered from TaCl5/Ph2CNH, the anion being probably generated by the action of adventitious water. Compounds 1–6 were characterized by elemental analysis, IR and NMR spectroscopy. The structures of 1, 4 and 6 were ascertained by X-ray diffraction studies.

The reactivity of niobium (tantalum) pentahalides with a selection of simple imines is described, including the first crystallographic characterization of a Nb(V)–azavinylidene complex.Figure optionsDownload as PowerPoint slide