Nitrogen dioxide, NO2, is a major industrial pollutant and can also be obtained by dehydration of nitric acid. NO2 is strong oxidant, and its high reactivity stems mainly from its paramagnetic character. Some porphyrin metal-NOx systems show moderate capabilities as oxidants, mostly stochiometric (non-catalytic) reactions.1,2 Polyoxometalates, on the other hand, have been widely used as "green" catalytic oxidants.3,4 Thus, we wished to modify Wells-Dawson transition metal substituted polyoxometalates with nitrogen dioxide, in order to find a new system for homogeneous catalytic oxidations.
In this study, we have found that such compounds are capable of oxidizing sulfides to the corresponding sulfoxides, and active C-H bonds leading, for example, to the oxidation of xanthene to xanthone. Additionally, it rapidly oxidizes water to yield hydrogen peroxide and also reacts in an ozonolysis-like reaction with stilbene derivatives to yield aldehydes. In these reactions, the POM-M-NO2 (M = Mn, Fe, Co, Ni, Cu) is always converted to the POM-M-NO. In addition to reactivity studies we present the characterization of the compounds and the mechanism of their reaction using multiple spectroscopic methods.
1. Kurtikyan, T. S.; Hovhannisyan , A. A.; Iretskii, A. V.; Ford, P. C. Inorg. Chem., 2009, 48, 11236–11241.
2. Heinecke, J. ; Ford. P. C. J. Am. Chem. Soc., 2010, 132, 9240–9243.
3. Neumann, R. Inorg. Chem., 2010, 49, 3594–3601.
4. N, Mizuno; K. Kamata. Coord. Chem. Rev., 2011, 255, 2358-2370.