Activation of Oxygenated Organics by Coordination to Niobium(V) and Tantalum(V) Halides

The coordination chemistry of group 5 metal pentahalides, MX5 (M = Nb, Ta, X = F, Cl, Br, I), with oxygen donor ligands was scarcely developed in the past. Our recent investigations on the reactivity of MX5 with oxygenated organics have evidenced the possibility that activation of the organic substrate occurs under mild conditions, resulting in new C–C 1 or C–O 2 bond formation. Interestingly, MX5 react with 1,2-dimethoxyethane (dme) affording MOX3(dme), CH3X and 1,4-dioxane; some intermediates have been isolated and characterized in the case of the reaction involving NbCl5, see scheme.3 The reaction has been generalized to a series of 1,2-dialkoxyalkanes, providing a new route for a fast and efficient synthesis of methyl-substituted dioxanes. The chemistry of MX5 with several O-organic species will be discussed with reference to the roles played by the halide and the stoichiometry.