Electron transfer in organometallic clusters. 2. Ferrocene-tricobalt carbon cluster compounds with multiple redox sites

Article abstract of DOI:10.1021/om50002a001

The redox chemistry of the cluster compounds (R)FcCCo₃(CO)_9-nL_n [R = H, n = 0 and 1 for L = PPh₃, P(C₆H₁₁)₃, and P(OR)₃ and n = 2 for L = P(OR)₃; R = Ac, n = 0] and (R)Fc(CO)CCo₃(CO)₉ (R = H, Me) has been studied by electrochemical and spectroscopic techniques. Regioisomers of the derivatives AcFcCCo₃(CO)₉ and MeFc(CO)CCo₃(CO)₉ were characterized. The prototypal FcCCo₃(CO)₉ forms a reversible redox series [1+,0] ? [0,0] ? [0,1-]. The reduction center is the cluster, and a radical anion was detected by ESR methods. Salts of the [1+,0] species were isolated and the IR, M?ssbauer, and electronic spectra confirm the positive site as the Fc moiety. Replacement of one CO by a Lewis base does not change the accessible oxidation states but the formation of [0,1-] becomes irreversible; cationic salts were characterized. The [1+,1+] oxidation state becomes accessible on the coordination of an additional Lewis base. A detailed analysis of the electrochemical and spectroscopic data suggests that there is a weak interaction between the redox sites, the cluster acting as an electron-withdrawing substituent to the Cp ring which in turn acts as a π donor to the cluster. A useful model is to regard one ring acting as a fulvene moiety interacting with a Co₃(CO)₉ cluster.