The electrochemical reactions between CO 2 and fac-Re(dpk)(CO) 3 Cl (1) are solvent dependent, controlled by the rate of diffusion of electroactive species from the electrode surface. Fast diffusion due to solvent or scan rate variations inhibits the carboxylation of the carbonylic carbon atom of the radical anion fac-Re{(C 5 H 4 N) 2 (CO) }(CO) 3 Cl (II) and leads to the generation of a coordinatively unsaturated fac-Re[(C 5 H 4 N) 2 {(CO) }](CO) 3 (VIII) that binds CO 2 at the metal center to form fac-Re[(C 5 H 4 N) 2 {(CO) }](CO) 3 (CO 2 ) (IX). Slow diffusion facilitates the carboxylation of the carbonylic carbon atom of II to form fac-Re[(C 5 H 4 N) 2 {C(O - (CO 2 )](CO) 3 (III) that undergoes a second electronic transfer followed by chemical steps leading to the formation of fac-Re[(C 5 H 4 N) 2 {C(O)(CO 2 H)}](CO) 3 (VI).