N-heterocyclic carbene and phosphine complexes of osmium and ruthenium carbonyls

1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene-silver(I)chloride ([IMes]AgCl), a carbene transfer agent, was employed in the reaction with various osmium clusters. Reaction of ([IMes]AgCl) with [Os3(µ-H)2(CO)10] gave [Os3(µ-H)(µ-Cl)(CO)9(IMes)] (1), an osmium N-heterocyclic carbene complex. The reaction of ([IMes]AgCl) with the cluster [Os3(CO)10(CH3CN)2] yielded two products, [Os3(µ-Cl)(CO)10(µ-Ag(IMes)] (2) and [(IMes-H)][Os3(µ-Cl)(CO)10](µ4-Ag)[Os3(µ-Cl)(CO)10] (3). Compound (2) is a heterobimetallic carbene complex resulting from the complete incorporation of ([IMes]AgCl). Transmetalation of the IMes fragment resulted in the formation of [Os4(µ-H)4(CO)11(n•IMes)] (4) (n denotes normal carbene bonding) and [Os4(µ-H)4(CO)10(IMes)2] (5). Compound (5) was found to be sensitive to silica gel column chromatography in the presence of dichloromethane decomposing to [Os4(µ-H)3(µ-Cl)(CO)11(IMes)] (6) which possessed a butterfly metal skeleton. The ruthenium analogue of (4), [Ru4(µ-H)4(CO)11(IMes)] (7), was prepared and found to be thermally unstable. Thermolysis of (4) in benzene yielded four products. The abnormal carbene complex [Os4(µ-H)4(CO)11(a•IMes)] (9) (a denotes abnormal carbene bonding), an isomer of (4), and {Os4(μ-H)(CO)10[(η-C)N(Mes)C2H2NC6H2 (CH3)2(η2-C)(η-C)C4H4(η2-C)]} (10), an unusual complex resulting from the activation of benzene, were isolated in modest yields. Two higher-nuclearity clusters, {Os5(µ5-C)(CO)14[η-C-η-NC2H2(Mes)]} (8) and [Os6(µ-H)4(µ5-C)(CO)15(IMes)] (11), both of which contain carbide ligands, were also isolated. {Os4(μ-H)(CO)10[(η-C)N(Mes)C2H2NC6H2(CH3)2(η2-C)(η-C)CHC(CH3)C2 H2(η2-C)]} (12), an analogue of (10), resulted from the thermolysis of (4) in toluene. Systematic synthesis of pentanuclear osmium hydride clusters was achieved by reaction of [Os4(µ-H)4(CO)12] with [Os(CO)4(PMe3)] giving three products, [Os5(µ-H)2(CO)15(PMe3)] (13), [Os5(µ-H)4(CO)14(PMe3)] (14) and [Os5(µ-H)2(CO)14(PMe3)] (15). (13) and (14) contain edge-bridged metal skeletons. Heating of (13) or (14) resulted in the formation of [Os5(µ-H)2(CO)14(PMe3)] (16), with a trigonal bipyramidal skeletal structure similar to (15) but differing in the location of the phosphine. Trinuclear mixed-metal clusters of the form [Ru2Os(CO)11(PR3)] (PR3 = PMe3, PEt3, P(OMe)3, PPh3, PMe¬2Ph, P(OCH2)3CMe), (17) to (22), have been systematically synthesized. The structure of the PMe3 derivative (17) had a staggered carbonyl conformation attributed to the electron-donating properties of the phosphorus ligand. Carbonyl exchange in the clusters was studied by 13CO labelling, if needed, and by variable-temperature 13C NMR spectroscopy.