ELECTROCHEMICAL-BEHAVIOR AND REACTIVITY OF CYCLOHEXADIENYL IRON COMPLEXES

The electrochemical behaviour of the monosubstituted cyclohexadienyl c omplexes [Fe(eta(5)-2-R-cyclohexadienyl) (CO)(3)] [PF6] (R = H, Me, n- Bu, MeO, Ph, MeOC(6)H(4), CF3C6H4), [Fe(eta(5)-1-EtO-cyclohexadienyl) (CO)(3)] [PF6], the disubstituted species [Fe(eta(5)-R,R'-cyclohexadie nyl) (CO)(3)] [PF6] (R = R' = MeO or Me; R = Me, R' = MeO), and [Fe(et a(5)-R-cyclohexadienyl) (CO)(2) (PPh(3))] [PF6] (R = H, Ph), was studi ed by cyclic voltammetry and controlled potential electrolysis. They u ndergo a single electron irreversible cathodic process at a potential which is dependent on the electronic properties of both the cyclohexad ienyl substituent and the co-ligands at the metal. In particular, tric arbonyliron complexes with aromatic substituents are reduced at signif icantly higher potentials than those with aliphatic ones, whereas subs titution of a carbonyl by a triphenylphosphine ligand lowers the catho dic potential. By cathodic controlled potential electrolysis, they und ergo C-C coupling and, in some cases (unsubstituted or alkoxy-substitu ted cyclohexadienyl complexes) also Fe-Fe coupling (with loss of CO) t o form the corresponding dimeric species. The formation of these produ cts has also been detected, in a number of cases, in the time-scale of the cyclic voltammetry.