ABSTRACT Selective conversion from [RuL2(CO)(η1-CO2)] to [RuL2(CO)(C(O)OH)]+ or [RuL2(CO)2]2+ (L = 2,2`- bipyridine) by adjustment of proton concentrations enables almost selective CO or HCOOH formation in electrochemical reduction of CO2 by [RuL2(CO)2]2+ in protic media. However, [RuL2(CO)2]2+ has no ability to catalyze multi-electron reduction of CO2 due to spontaneous dissociation of CO from the reduced form of the complex. Replacement of a CO group in [RuL2(CO)2]2+ by a polypyridyl ligand (L`) effectively stabilizes the two electron reduced form of [RuL2(L`)(CO)]2+. Electrochemical reduction of CO2 by [RuL(trpy)(CO)]2+ (trpy = terpyridien) at -1.50 V (vs. SCE) produced not only HCOOH and CO but also HCHO, CH3OH, HOOCCHO and HOCH2COOH in CH3CN/H2O at -20°C, in which the CO2 reduction proceeds via Ru- η1 -CO2, Ru-C(O)OH, Ru-CO, Ru-CHO and Ru-CH2OH intermediates. The formation of 4- and 6-electron reduced products in the CO2 reduction results from protonation and carboxylation of the Ru-CHO and Ru-CH2OH intermediates. Furthermore, electrochemical CO2 reduction by [RuL2(qu)(CO)]+ (qu = quinoline) in the presence of (CH3)4N+ or CH3I in dry CH3CN catalytically produces CH3C(O)CH3, CH3C(O)CH2COO- and HCOO-. The latter two are the products of the carboxylation reaction of the former by [RuL2(qu)(CO2)]0. Double alkylation of [RuL2(qu)(CO)]0 with CH3I or (CH3)4N+ through [RuL2(qu)(C(O)CH3)]+ forms acetone under electrolysis conditions.
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