Syntheses of some organogoldtriosmium clusters; X-ray crystal structure of [Os₃(CO)₈(PPh₃){Au(PPh₃)}(2-NHC ₅H₄N)]

The clusters [Os₃(CO)₉{Au(PPh₃)}(C₂Ph)] (1), [Os₃(CO)₁₀{Au(PPh₃)}(OH)] (2), [Os₃(CO)₁₀{Au(PPh₃)}(NHSO₂C ₆H₄Me-p)] (3), and [Os₃(CO)₈(Y){Au(PPh₃)}(2-NHC₅H ₄N)] [Y = PPh₃ (4) or CO (5)] were prepared from the appropriate neutral osmium cluster and chloro(triphenylphosphine)gold(I). [Os₃(CO)₈(PPh₃){Au(PPh₃)}(2-NHC ₅H₄N)] (4) was shown by X-ray analysis to consist of an isosceles triangle of osmium atoms substituted by an equatorial phosphine ligand and eight carbonyls. A 2-pyridylamido ligand caps one side of the Os₃ triangle and a (triphenylphosphine)aurio group bridges the longest Os-Os bond. The complex crystallises in space group P2₁/n with a = 14.567(5), b = 18.010(24), c = 18.456(7) Å, β = 92.22(3)°, and Z = 4. The structure was solved by a combination of direct methods and Fourier-difference techniques, and refined by blocked-cascade least-squares methods to R = 0.065 to 3 541 observed diffractometer data.