Effect of added donor ligands on the selective oxygenation of organic sulfides by oxo(salen)chromium(V) complexes

Abstract

Abstract Oxo(salen)chromium(V) complexes, [(salen)Cr V O] + , oxidize organic sulfides selectively to sulfoxides in high yield. This oxygenation reaction is catalyzed by ligand oxides (LO's), pyridine N -oxide, 4-picoline N -oxide, 4-phenyl pyridine N -oxide and triphenylphosphine oxide. The rate is accelerated by 10–20 times with an increase in yield of sulfoxide in less reaction time. This catalytic activity is highly sensitive to the nature of the substituent in the phenyl ring of ArSMe and in the 3- and 5-position of the salen ligand. The reaction constant ( ρ ) value obtained with the ligand oxide catalyzed reaction is low compared to the value in the absence of LO. The strong binding and catalytic activity of ligand oxides on the oxo(salen)chromium(V) ion oxygenation is explained in terms of binding constants and a mechanism involving the electrophilic attack of [(salen)Cr V O] + –LO adduct on the sulfur centre of phenyl methyl sulfide.