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.