REDOX CHEMISTRY AND SUBSTITUTION-REACTIONS OF THE MU-CYANOALKYLIDENE COMPLEXES [FE-2(CO)(2)(CP)(2)(MU-CO)(MU-C(CN)(X))](N+) (N=O, X=CN, H, ME, SME, OME, OET, OPH, OCH2CH=CH2, PET(2), OR NC5H10, N=1, X=PME(2)PH)

Electrochemistry of the mu-cyanoalkylidene complexes [Fe-2(CO)(2)(cp)(2)(mu-CO){mu-C(CN)(X)}](n+) (n = 0, X = CN, H, Me, SMe, OMe, OEt, OPh, OCH2CH=CH2, PEt(2), piperidinyl; n = 1, X = PMe(2)Ph) in nonaqueous solutions shows a one-electron reduction to the corresponding paramagnetic monoanions, which have been characterized by EPR spectroscopy. The presence of the positive charge in [Fe-2(CO)(2)(cp)(2)(mu-CO){mu-C(CN)(PMe(2)Ph)}](+) makes the one-electron addition significantly easier than to the neutral complexes. None of the 19-electron anions are fully stable and all undergo slow decomposition reactions, the rates of which are a function of the X substituent. Access to the radical anion intermediates [Fe-2(CO)(2)(cp)(2)(mu-CO){mu-C(CN)(X)}](-) does not trigger Electron Transfer Chain catalytic substitution reactions of CO by phosphines, but allows these reactions to be successfully carried out by different methods, such as chemical reduction, CO photolysis and use of Me(3)NO. The CO-substituted derivatives [Fe-2(cp)(2)(CO)(PMe(2)Ph)(mu-CO){mu-C(CN)(X)}] (X = CN, H, SMe) and [Fe-2(cp)(2)(mu-CO)(mu-dppm){mu-C(CN)(X)}](n) (X = H, CN; dppm = Ph(2)PCH(2)PPh(2)) were obtained. The one-electron reduction of the monophosphine-substituted complexes is fully irreversible and occurs at potentials 0.3-0.4 V more negative than those of the corresponding precursors. The different methods for promoting CO displacement in the mu-alkylidene complexes have been compared; the photolytic method affords the highest yields.