Publication 821

Chem. Eur. J., 23 (20), 4782-4793, 2017 DOI:10.1002/chem.201605546
Local Proton Source in Electrocatalytic CO2 Reduction with [Mn(bpy-R)(CO)3Br] Complexes

Department of Chemistry and NIS University of Turin Turin Italy
Univ. Paris Diderot, Sorbonne Paris Cité, UMR CNRS 7591 Laboratoire Electrochimie Moléculaire Paris 13 France

The electrochemical behavior of fac-[Mn(pdbpy)(CO)₃Br] (pdbpy=4-phenyl-6-(phenyl-2,6-diol)-2,2′-bipyridine) (1) in acetonitrile under Ar, and its catalytic performances for CO₂ 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 CO₂-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 CO₂ 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 CO₂ reduction pathways. Furthermore, a comparative investigation performed on the new fac-[Mn(ptbpy)(CO)₃Br] (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 CO₂.