Convenient synthesis of fluoride-alkoxides of Nb(V) and Ta(V): a spectroscopic, crystallographic and computational study

The synthesis and the spectroscopic characterization of fluoride-alkoxides of niobium and tantalum in the highest oxidation state are reported. Suspensions of MF 5 (M = Nb, Ta) in a chlorinated solvent reacted with up to three equivalents of ROSiMe 3 (R = Me, Et, Ph) to afford polynuclear derivatives and variable amounts of FSiMe 3. Thus MF 4(OR) (R = Et, Ph) and MF 3(OR) 2 were obtained by selective 1:1 and 1:2 reactions almost exclusively as single isomeric products; otherwise mixtures of MF 4(OMe) species were afforded from the equimolar reactions of MF 5 with MeOSiMe 3. The 1:3 reaction of TaF 5 with MeOSiMe 3 led to different forms of TaF 2(OMe) 3. The synthesis of TaF(OPh) 4 was forced by high temperature conditions or the use of a large excess of PhOSiMe 3. DFT studies were carried out in order to predict, in the distinct cases, the most stable structures of the metal products. The molecular structures of [NbF 2(OPh) 2(μ-F)] 3 and [TaF(OPh) 3(μ-OPh)] 2 were ascertained by X-ray diffraction. © 2012 The Royal Society of Chemistry.