Metal-salen complexes as efficient catalysts for the oxygenation of heteroatom containing organic compounds-synthetic and mechanistic aspects

The metal-salen complexes (metal = Mn, Cr, Fe, Ru, Co, V and Ti) find widespread use as efficient catalysts for the selective oxygenation of organic sulfides, sulfoxides and aromatic amines. The active oxidant can be generated from the metal-salen ion using PhIO, H2O2, t-BuO2H and ClO− as the oxygen source. The catalytic activity of these complexes can be finely tuned by introducing substituents in the 3- and 5-positions of the salen ligand. As far as Cr(V) oxidation of amine is concerned, the addition of donor ligand is indispensable to get the oxygenated product. In the absence of donor ligand, oligomerization is a predominant process. Organic sulfoxides perform dual role as substrates and as donor ligand. This review summarizes recent studies on the metal-salen ion catalysed oxygenation of heteroatom containing organic compounds, in particular, those incorporating sulfur and nitrogen.