ansa-metallocene derivatives : XIV. Electrochemical reactions of unbridged and of tetramethylethanediyl-bridged chromocene carbonyl complexes

(C5H5)2Cr(CO), formed from chromocene and CO gas in THF solution at 0°C, loses its CO ligand upon one-electron oxidation. No CO loss is observed, on the other hand, when the ansa-chromocene carbonyl complex (CH3)4C2(C5H4)2Cr(CO) is oxidised to its monocation. Formation of a dication (CH3)4C2(C5H4)2Cr(CO)2+, for which there is no unbridged analogue, is irreversible owing to its fast conversion to a solvent adduct; its reduction under CO, however, quantitatively regenerates the neutral carbonyl complex. One-electron reduction of either of the carbonyl complexes, (C5H5)2Cr(CO) or (CH3)4C2(C5H4)2Cr(CO), induces a fast, irreversible decay of the chromocene framework