The Reactivity of Halides of High-Valent Group 5 and 6 Elements with Organic Compounds: from Coordination Chemistry to Activation Reactions

Niobium and tantalum pentahalides, molybdenum pentachloride and tungsten hexachloride are easily-available solid compounds, whose coordination chemistry was scarcely elucidated in the past. We have been involved in a systematic exploration of the reactivity of such halides with stoichiometric amounts of oxygen- and/or nitrogen-containing organic species. This approach provides the way to a variety of inorganic structural motifs [1]. Furthermore, the coordination to the metal centre may represent the preliminary step of transformation of the organic substrate, which usually takes place selectively and under mild conditions [2]. In a number of cases, the process results in the formation of stable metal-anion salts containing otherwise reactive organic cations [3]. The metal-halide bond energy value and the availability to the metal centre of a one-electron reduced oxidation state are the two key factors which drive the activation reactions, and provide uniqueness with respect to the parallel chemistry exhibited by high-valent main group element halides. Examples will be given with reference to arenes, natural α-aminoacids, alkyl-ureas, amines, etc.