Nucleophilic addition via metal-metal bond cleavage in an osmium-antimony cluster

The room-temperature reaction of a number of two-electron nucleophiles with the osmium-antimony cluster [Os₃(μ-H)(CO)₁₀(μ-SbPh₂)] 1 gave adducts [Os₃H(CO)₁₀(μ-SbPh₂)L] 2 (L = PPh₃ a, AsPh₃ b, SbPh₃ c or CO d), in which the antimony-bridged Os-Os bond has been cleaved in order to accommodate the incoming ligand. X-Ray crystallographic studies on 2b and 2c confirmed that the ligands L occupied an equatorial site of the Os₃Sb framework, while NMR studies indicated that the clusters 2a-2c existed as isomeric mixtures, which probably differ in the arrangements of the ligand L relative to the antimony vertex. The reaction leading to the formation of 2b, which was carried out at elevated temperature, also led to decarbonylation to a substituted analogue of 1 in which the ligand L was on the unbridged osmium.