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

Abstract Ten complexes [(η 6 -(arene)OsCl(C 5 H 4 N-2-CH=N-C 6 H 5 X)]PF 6 (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 [(η 6 -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 1 H and 13 C 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 NaIO 4 as terminal oxidant in a H 2 O/t-BuOH biphasic system. All of the compounds were very effective catalysts for this reaction and gave the corresponding aldehyde in high yields.