Reaction Pathways for fac-Os(CO)3(MeCN)Me2 with Mono- and Bidentate Ligands

Abstract

The reactions of fac-Os(CO)3(L)Me2 (1a, L = MeCN; 1b, L = THF) with monodentate and bidentate ligands have been studied for the first time. Treatment of 1a or 1b with PPh3 gives fac-Os(CO)3(PPh3)Me2 (2), which may be further reacted with Me3NO in acetonitrile to give the unexpected isomer cis-Os(CO)2(PPh3)(MeCN)Me2 (3). Subsequent reaction of 3 with PPh3 gives cis,trans-Os(CO)2(PPh3)2Me2 (4), with a further isomerization accompanying the ligand substitution. Oxidative decarbonylation of 4 with Me3NO was found not to be possible. Treatment of 1a or 1b with bidentate ligands gives different reaction products, depending on the choice of ligand, the reaction conditions, and the stoichiometry. Reactions with small-bite-angle bidentate ligands (L-L) gave the compounds cis-Os(CO)2(L-L)(COMe)Me (5a, L-L = dppm; 5b, L-L = dppe; 5c, L-L = 2,2‘-bipy). These mixed methyl acetyl complexes are formed by displacement of the labile ligand and subsequent chelation, accompanied by methyl migration onto carbonyl. Reaction of 1a with 1 equiv of dppp, however, resulted in a series of reactions which led to the formation of the decarbonylated product cis-Os(CO)2(dppp)Me2 (7). However, reaction of 1a with 0.5 equiv of dppp gave the bimetallic dppp-bridged complex [fac-Os(CO)3Me2]2(μ-dppp) (8). In addition to characterization of all the new compounds by analytical and spectroscopic techniques, the molecular structures of 5a and 8 have been determined by X-ray diffraction.