Redox chemistry and substitution reactions of the μ-cyanoalkylidene complexes [Fe 2(CO) 2(cp) 2( μ-CO){ μ-C(CN) (X)}] n+ ( n = 0, X = CN, H, Me, SMe, OMe, OEt, OPh, OCH 2CH = CH 2, PEt 2, or NC 5H 10; n = 1, X = PMe 2Ph)

Abstract

Electrochemistry of the μ-cyanoalkylidene complexes [Fe 2(CO) 2(cp) 2( μ-CO){ μ-C(CN)(X)}] n+ ( n = 0, X = CN, H, Me, SMe, OMe, OEt, OPh, OCH 2CH=CH 2, PEt 2, piperidinyl; n = 1, X = PMe 2Ph) 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(μ-CO){μ-C(CN)(PMe 2Ph)}] + 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(μ-CO){μ-C(CN)(X)}] − does not trigger Electron Tra 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 3NO. The CO-substituted derivatives [Fe 2(cp) 2(CO)(PMe 2Ph)(μ-CO){μC(CN)(X) (X = CN, H, SMe) and [Fe 2(cp) 2( μ-CO)( μ-dppm){ μ-C(CN)(X)}], (X = H, CN; dppm = Ph 2PCH 2PPh 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 μ-alkylidene complexes have been compared; the photolytic method affords the highest yields.