Unusual activations of oxygen molecules by early transition metal chlorides

NbCl5, MoCl5 and WCl6 are commercial non expensive compounds, which have found application in material and synthetic chemistry. Nonetheless the knowledge about the direct interaction of these transition metal halides with stoichiometric amounts of organic molecules is far from being well understood. Recently, our systematic study on the chemistry of MX5 (M = Nb, Ta; X = halide) with oxygen donors has provided evidence of interesting and unusual features.1 Here we report the distinct activation routes followed by a series of simple carbonyl-containing molecules when contacted with the cited chlorides. For instance, natural aminoacids are deoxygenated by MoCl5, whereas rare decarboxylation to iminium may occur with NbCl5 (Figure 1). Furthermore WCl6 acts as efficient chlorinating agent towards ketones and amides. In particular, the reaction with acetanilide proceeds with CN coupling and yields acylamidinium salt in mild conditions (Figure 2).