Electrochemical reduction of [(Ir(eta(5)-C5Me5))(3)(mu(3)-S)(2)](BPh4)(2) ([Ir3S2](BPh4)(2)) in CO2-saturated CH3CN at -1.30 V (vs Ag/AgCl) produced C2O42- and [(Ir(eta(5)-C5Me5))(2)(Ir(eta(4)-C5Me5)CH2CN)(mu(3)-S)(2)](+) ([Ir3S2CH2CN](+)). The crystal structure of [Ir3S2CH2CN](BPh4) by X-ray analysis revealed that a linear CH2CN group is linked al the exo-position of a C5Me5 ligand, and the C5Me5CH2CN ligand coordinates to an Ir atom with an eta(4)-mode. The cyclic voltammogram of [Ir3S2CH2CN](+) in CH3CN under CO2 exhibited a strong catalytic current due to the reduction of CO2, while that of [Ir3S2](2+) did not show an interaction with CO2 in the same solvent. The reduced form of [Ir3S2CH2CN](+) works as the active species in the reduction of CO2. The IR spectra of [Ir3S2CH2CN](+) in CD3CN showed a reversible adduct formation with CO2 and also evidenced the oxalate generation through the reduced form of the CO2 adduct under the controlled potential electrolysis of the solution at -1.55 V. A coupling reaction of two CO2 molecules bonded on adjacent mu(3)-S and Ir in [Ir3S2CH2CN](0) is proposed for the first catalytic generation of C2O42- without accompanying CO evolution.