Tris(N-pyrrolyl)phosphine complexes of osmium(II) and osmium(0)

Reaction between OsHCl(CO)(PPh3)3 and the powerful π-accepting ligand tris(N-pyrrolyl)phosphine, P(NC4H4)3, results in replacement of the PPh3 ligand trans to hydride giving OsHCl(CO)[P(NC4H4)3](PPh3)2 (1). The analogue of 1 with Cl replaced by p-tolyl, OsH(p-tolyl)(CO)[P(NC4H4)3](PPh3)2 (3), is accessible by thermal decarboxylation of Os(p-tolyl)(η2-O2CH)(CO)(PPh3)2 (2) in the presence of P(NC4H4)3. Complex 3, despite having cis-hydride and p-tolyl ligands, is resistant to reductive elimination of toluene. Osmium(0) complexes containing P(NC4H4)3 are conveniently prepared by replacement of one PPh3 ligand from Os(CO)(CE)(PPh3)3 (E=O, S) to give Os(CO)(CE)[P(NC4H4)3](PPh3)2 (4, E=O; 5, E=S). Structure determination of 4 confirms a trigonal bipyramidal geometry with the PPh3 ligands in the axial positions and the π-accepting P(NC4H4)3 ligand in the expected equatorial site.