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 [Os-3(mu-H)(CO)(10)(mu-SbPh2)] 1 gav e adducts [Os3H(CO)(10)(mu-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 o rder to accommodate the incoming ligand. X-Ray crystallographic studie s on 2b and 2c confirmed that the ligands L occupied an equatorial sit e of the Os3Sb framework, while NMR studies indicated that the cluster s 2a-2c existed as isomeric mixtures, which probably differ in the arr angements of the ligand L relative to the antimony vertex. The reactio n leading to the formation of 2b, which was carried out at elevated te mperature, also led to decarbonylation to a substituted analogue of 1 in which the ligand L was on the unbridged osmium.