SINGLET OXYGEN AND THE PRODUCTION OF SULFUR OXYGENATES OF NICKEL(II) AND PALLADIUM(II) THIOLATES

The metal dithiolate s(2-mercaptoethyl)-1,5-diazacyclooctane]nickel(II ) (Ni-1), a sterically hindered analogue (Ni-1), and the palladium an alogue Pd-l react with (1) Delta O-2 to yield a variety of stable and isolable metallosulfones (MS(O-2)R) and metallosulfoxides (MS(O)R). Si nglet oxygen was generated both photochemically with the sensitizer Ro se Bengal and thermally by decomposition of the 1,4-endoperoxide of 1, 4-dimethylnaphthalene. Increased rates and oxygenation yields are obse rved upon excitation of O-2 from its ground state, (3) Sigma, to the e xcited state, (1) Delta. The reactions are both solvent and concentrat ion dependent, with sulfones generally favored in acetonitrile and sul foxides favored in methanol. There is also a ligand and metal effect. The proposed mechanistic pathways involving a persulfoxide precursor t o single sulfur site O-2 addition (producing metallosulfones) and adja cent sulfur site O-2 addition (producing metallosulfoxides) are consis tent with product distribution, comparison to the much studied oxygena tion of organic sulfides, and previous isotopic labeling experiments.