ELECTRON TRANSFER IN ORGANOMETALLIC CLUSTERS XI. REDOX CHEMISTRY OF M3(CO)12 (M = Ru, Os) AND PPh3 DERIVATIVES; MECHANISM OF CATALYSED NUCLEOPHILIC SUBSTITUTION

Article abstract of DOI:10.1016/0022-328X(87)85060-X

The generality of a two-electron reduction process involving an mechanism has been established for M3(CO)12 and M3(CO)_12-n(PPh3)_n (M = Ru, Os) clusters in all solvents.Detailed coulometric and spectral studies in CH2Cl2 provide strong evidence for the formation of an 'opened' M3(CO)12^2- species the triangulo radical anions M3(CO)12^<*> having a half-life of < 10^-6 s in CH2Cl2.However, the electrochemical response is sensitive to the presence of water and is concentration dependent.An electrochemical response for 'opened' M3(CO)12^2- is only detected at low concentrations < 5*10^-4 mol dm^-3 and under drybox condition.The electroactive species found at higher concentrations and in the presence of water M3(CO)11^2- and M6(CO)18^2- were confirmed by a study of the electrochemistry of these anions in CH2Cl2; HM3(CO)11^- is not a product.The couple ^-/2- is chemically reversible under certain conditions but oxidation of HM3(CO)11^- is chemically irreversible.Different electrochemical behaviour for Ru3(CO)12 is found when (X = OAc^-, Cl^-) salts are supporting electrolytes.In these solutions formation of the ultimate electroactive species <μ-C(O)XRu3(CO)10>^- at the electrode is stopped under CO or at low temperatures but Ru3(CO)12^- is still trapped by reversible attack by X presumably as <η¹-C(O)XRu3(CO)11>^-.It is shown that electrode-initiated electron catalysed substitution of M3(CO)12 only takes place on the electrochemical timescale when M = Ru, it is slow, inefficient and non-selective, whereas BPK-initiated nucleophilic substitution of Ru3(CO)12 is only specific and fast in ether solvents particularly THF.Metal-metal bond cleavage is the most important influence on the rate and specificity of catalytic substitution by electron or -initiation.The redox chemistry of M3(CO)12 clusters (M = Fe, Ru, Os) is a consequence of the relative rates of metal-metal bond dissociation, metal-metal bond strength and ligand dissociation and in many aspects resembles their photochemistry.