Bond activation by electron transfer in indenyl ruthenium(II) cpmplexes. The electrochemical reduction of [Ru(eta5-C9H7)ClL2] and [Ru(eta5-C9H7)L2]+

The reduction of half-sandwich indenyl complexes of general formula [Ru(eta(5)-C9H7)Cl(L)(2)] (L = PPh3, 1; L-2 = 1,5-cyclooctadiene, 2) and [Ru(eta(5)-C9H7)(L)(2)](+) has been carried out in order to investigate the effects of electron transfer on the structural and chemical properties of the complexes. The reduction of these complexes proceeds by irreversible bielectronic processes. In the case of the metal halide complexes, the first electron transfer generates a 19-electron radical anion, which undergoes Ru-Cl bond cleavage to form a 17-electron Ru-eta(5)-C9H7)(L)(2) radical, which is in turn reduced at a less negative potential. Therefore the overall process proceeds according to a ECE mechanism, characterized by two electron transfers separated by a chemical reaction. The cationic [Ru(eta(5)-C9H7)(L)(2)](+) complexes were generated in situ by chloride abstraction, upon reacting complex 1 or 2 with AgBF4 or AgPF6; both [Ru(eta(5)-C9H7)(PPh3)(2)](+) (1a(+)) and [Ru(eta(5)-C9H7)COD](+) (2a(+)) undergo a monoelectronic reductive process forming the radical intermediates, which rapidly dimerize. The [Ru(eta(5)C(9)H(7))COD]. radical is sufficiently stable to be detected by cyclic voltammetry and partially generates the 18-electron anion [Ru(eta(5)-C9H7)COD](-).