Oxidation of organic sulfides into sulfoxides under low-power light irradiation photocatalyzed by metallophthalocyaninate-capped 3d-metal tris-pyridineoximates

Abstract

A series of iron-, nickel(II)- and cobalt(III)-centered zirconium- and hafnium(IV)phthalocyaninate-capped tris-pyridineoximates was prepared in their yields from moderate to relatively high using the template condensation of 2-acetylpyridineoxime as a chelating ligand synthon with equimolar amount of metal(IV)phthalocyaninate (M(IV)Zr(IV), Hf(IV)) as a capping Lewis acidic agent on the corresponding 3d-metal ion as a matrix. In the case of cobalt complexes, an oxidation of the initial Co²⁺ ions occurred in a course of the template self-assembly reactions. Variation of both the capping and the including encapsulated metal ions were found to affect their photochemical properties, photostability and photocatalytic activity. Iron- and nickel(II)-centered complexes of this type are most photostable under a light irradiation. The zirconium(IV)phthalocyaninate-capped nickel(II) tris-pyridineoximate possesses an excellent photocatalytic activity in the tested sulfoxidation reactions. It selectively catalyzes oxidation of a wide range of various organic sulfides, such as aromatic, aliphatic and cyclic substrate, as well as those with substituent prone to oxidation. In the performed large-scale (10 mmol) oxidation experiments with thioanizole and dibenzylsulfoxide as the substrates, the isolated yields of their target sulfoxide derivatives became of 98–99 % with the catalytic turnover numbers up to 2·10⁴.