Ring opening versus phenyl–phosphorus bond cleavage in incorporating a phosphole into triosmium clusters

Abstract

The five-membered heterocyclic compound 3,4-dimethyl-1-phenylphosphole (Ph[graphic omitted]H) reacts with [Os₃(CO)₁₁(MeCN)] or [Os₃(CO)₁₀(MeCN)₂] to give the simple substitution products [Os₃(CO)_12–x(PhPC₄H₂Me₂)_x](x= 1 or 2) in which the phospholes are co-ordinated as tertiary phosphines through the phosphorus atoms. Thermolysis of these compounds gives decarbonylation compounds containing modified phosphole ligands. Phosphorus–carbon bonds either to the phenyl group or within the five-membered ring have been cleaved. The X-ray structure of the main product [Os₃(CO)₉(µ₃-PhPCHCMeCMeCH)]1 shows that the organic µ₃ ligand is a six-electron donor which is co-ordinated differently from the corresponding eight-electron donating ligand derived from 1-phenylphosphole in the cluster [Os₃(CO)₉(µ₃-PhPCHCHCHCH)]. There is evidence for the reversible generation of this alternative from, 3, of the methylated compound 1 by photolysis. A minor product of the thermolysis is the hydrido cluster [Os₃(µ-H)(µ-[graphic omitted]H)(µ₃-C₆H₄)(CO)₉]2 which contains a five-membered phospholyl ring and an o-phenylene (benzyne) ligand which originated from the phenyl group. The X-ray structure shows that the phospholyl ligand bridges two osmium atoms as a phosphido ligand through the phosphorus atom. The major and minor products, 1 and 2, are both derived by C–P bond cleavage, either in the phosphole ring or to the phenyl substituent respectively.