Mechanistic insights into CO 2 conversion to CO using cyano manganese complexes.

Without the use of a photosensitizer, [Mn(bpy)(CO) 3 (CN)] (MnCN) can photochemically form [Mn(bpy)(CO) 3 ] - , the active species for CO 2 reduction. While cases of the axial X-ligand dissociating upon irradiation of fac -[M(N-N)(CO) 3 X] complexes (M = Mn or Re; N-N = bipyridine (bpy) ligand; X = halogen or pseudohalogen) are well documented, the axial cyanide ligand is retained when either [Mn(bpy)(CO) 3 (CN)] or [Mn(mesbpy)(CO) 3 (CN)], MnCN(mesbpy), are irradiated anaerobically. Infrared and UV-vis spectroscopies indicate the formation of [Mn(bpy)(CO) 2 (MeCN)(CN)] (s-MnCN) as the primary product during the irradiation of MnCN. An in-depth analysis of the photochemical mechanism for the formation of [Mn(bpy)(CO) 3 ] - from MnCN is presented. MnCN(mesbpy) is too sterically hindered to undergo the same photochemical mechanism as MnCN. However, MnCN(mesbpy) is found to be electrocatalytically active for CO 2 reduction to CO. Thus providing an interesting distinction between photochemical and electrochemical charge transfer.