Anionic and Mononuclear Phosphinidene and Imide Complexes of Niobium

The
reactivity of a terminal methylidene complex of niobium, [(ArO)2NbCH2(CH3)­(CH2PPh3)] (1), with the primary phosphine PhPH2 results in formation of the anionic phosphinidene complex [H3CPPh3]­[(ArO)2NbPPh­(CH3)2] (2), where both the methylidene and ylide
ligands of the precursor experience protonation. Multinuclear NMR
spectroscopy and X-ray diffraction studies indicate formation of a
bent phosphinidene ligand. Similar reactivity is also observed with
primary amines, specifically AdNH2 (Ad = 1-adamantyl) and
MesNH2 (Mes = 2,4,6-trimethylphenyl), resulting in formation
of the corresponding imide complexes [H3CPPh3]­[(ArO)2NbNR­(CH3)2] (R =
Mes, (3), Ad, (4)). Whereas 2 has a bent phosphinidene
ligand and pseudo trigonal bipyramidal structure, the solid-state
structure determination of complex 4 reveals a linear
imide ligand and square-pyramidal geometry, where the imide enjoys
significant Nb–NR multiple-bond character.