Oxidation of olefins catalyzed by half-sandwich osmium(II) arene complexes

Abstract

Ten complexes [(η6-(arene)OsCl(C5H4N-2-CH=N-C6H5X)]PF6 (with arene = p-cymene (1) or benzene (2); X = 4-F (a), 4-Cl (b), 4-Br (c), 4-I(d) and 4–methyl (e)) were synthesized by reacting the corresponding N,N′-bidentate ligands with the osmium arene dimers [(η6-arene)Os(μ-Cl)Cl]2 in a 2:1 ratio. Complexes 1a-e and 2c-d are new. The compounds were fully characterized via 1H and 13C NMR, IR and UV–Vis spectroscopy, and elemental analyses. The x-ray crystal structure of compound 2e is also reported. The Os(II) complex shows the expected “ piano stool” type geometry. These Os(II) compounds were investigated in the catalytic oxidation of olefins to carbonyl compounds with NaIO4 as terminal oxidant in a H2O/t-BuOH biphasic system. All of the compounds were very effective catalysts for this reaction and gave the corresponding aldehyde in high yields.