Ligand substitution in the osmium carbonyl cluster Os₂(CO)₈(µ₃-SbPh)Os(CO)₃(Cl)₂: Towards derivatives of the osmostibine metalloligand

Derivatisation of the osmium carbonyl cluster Os₂(CO)₈(µ₃-SbPh)Os(CO)₃(Cl)₂, 1, the precursor to the metalloligand Os₂(CO)₈(µ-SbPh), 2, was explored as a route to derivatives of the latter. The reaction of 1 with PPh₃ in different stoichiometries and under trimethylamine N-oxide activation in CH₃CN led to mono-, di-, tri- and tetra-substitution by PPh₃ and CH₃CN. The first substitution occurred at the Os(CO)₃Cl₂ “spike” and although subsequent substitution favoured CH₃CN at the osmostibine moiety, the latter was not readily displaced by PPh₃. Substitution at the “spike” also shut down release of the substituted osmostibine. The CH₃CN-substituted osmostibine could, however, be generated in situ through the bis-acetonitrile derivative of 1 by conversion of the Os(CO)₂(NCCH₃)Cl₂ “spike” back into its removable Os(CO)₃Cl₂ form through reaction with CO gas, and was then trapped with W(CO)₅(NCCH₃).