Selective and mild oxidation of sulfides to sulfoxides with H2O2 catalyzed by copper(II) asymmetrical tetradentate Schiff base complex

Selective oxidation of sulfides to sulfoxides without any over-oxidation to sulfones is a challenging research interest in synthetic organic chemistry, partly because of theimportance of sulfoxides as intermediates in biologically active compounds [1]. Among all methods described so far, the oxidation of sulfides by various metal catalysts is one of the most attractive routes. Schiff base transition metal complexes, due to their easy synthesis and thermal stability, are used as catalysts in various organic reactions such as oxidation, epoxidation and polymerization of alkenes [2]. Recently, much effort has been paid to symmetrical Schiff base ligand due to the bonding of central metal ions with asymmetrical ligand in natural systems [3]. In this work, the copper(II) asymmetrical Schiff base complex (1) was synthesized according to published method [3]. The prepared complex 1 was successfully used as a homogeneous catalyst for selective oxidation of sulfides to sulfoxides at room temperature (Fig. 1). Good to high yield of products, use of hydrogen peroxide as a green oxidant and no by-product formation can be mentioned as advantages of this method for oxidation of sulfides