NMR characterization of four new isomers of H(mu-H)Os-3(CO)(10)(phosphine)

An investigation of the low temperature reaction of H2Os3(CO)(10) with phosphines afforded four novel isomeric derivatives of the H(mu-H) Os-3(CO)(10)(phosphine) adduct in addition to the previously reported one. Their structures have been suggested on the basis of H-1 C-13 and P-31 NMR data. They represent the kinetically favoured isomers which slowly transform into the most thermodynamically stable derivative containing the phosphine Ligand trans to an Os-Os bond and cis to the bridging hydride. in some cases it has been possible to measure the rate of disappearance of these adducts at different temperatures from which an estimation of the activation energies associated with their transformation to the final product has been obtained. The results herein reported show that the phosphine may occupy either axial and equatorial sites at the osmium bearing the bridging hydride and, in the case of the PPh3, derivative, an equatorial site at the osmium bearing the terminal hydride as well. Thus, five of the 11 theoretically possible isomers of H(mu-H)Os-3(CO)(10)(phosphine) have been detected and characterized. (C) 1998 Elsevier Science S.A. All rights reserved.