Local Proton Source in Electrocatalytic CO2 Reduction with Mn(bpy–R)(CO)3Br Complexes

Abstract The electrochemical behavior of fac ‐Mn(pdbpy)(CO) 3 Br (pdbpy=4‐phenyl‐6‐(phenyl‐2,6‐diol)‐2,2′‐bipyridine) ( 1 ) in acetonitrile under Ar, and its catalytic performances for CO 2 reduction with added water, 2,2,2‐trifluoroethanol (TFE), and phenol are discussed in detail. Preparative‐scale electrolysis experiments, carried out at −1.5 V versus the standard calomel electrode (SCE) in CO 2 ‐saturated acetonitrile, reveal that the process selectivity is extremely sensitive to the acid strength, producing CO and formate in different faradaic yields. A detailed spectroelectrochemical (IR and UV/Vis) study under Ar and CO 2 atmospheres shows that 1 undergoes fast solvolysis; however, dimer formation in acetonitrile is suppressed, resulting in an atypical reduction mechanism in comparison with other reported Mn I catalysts. Spectroscopic evidence of Mn hydride formation supports the existence of different electrocatalytic CO 2 reduction pathways. Furthermore, a comparative investigation performed on the new fac ‐Mn(ptbpy)(CO) 3 Br (ptbpy=4‐phenyl‐6‐(phenyl‐3,4,5‐triol)‐2,2′‐bipyridine) catalyst ( 2 ), bearing a bipyridyl derivative with OH groups in different positions to those in 1 , provides complementary information about the role that the local proton source plays during the electrochemical reduction of CO 2 .