Effect of PDI ligand binding pattern on the electrocatalytic activity of two Ru(II) complexes for CO2 reduction

The electrochemical properties of two complexes, [RuII(η3‐(N,N,N)‐OMePDI)Cl2(PPh3)]0 (1) and [RuII(η2‐(C,N)‐OMePDI‐H)Cl (PPh3)2]0 (2), were studied. In octahedral complex 1, bis(imino)pyridine (PDI) is a tridentate η3‐N,N,N‐coordinated ligand, whereas in trigonal‐bipyramidal complex 2, the deprotonated PDI ligand adopts the unusual bidentate binding mode η2‐C,N to coordinate to the central Ru(II) ion. Bulk electrolysis in two electrolyte solutions of acetonitrile (MeCN) and tetrahydrofuran (THF) suggests that complexes 1 and 2 have very different electrocatalytic CO2 reduction activities. In MeCN solution, complex 1 can selectively electrocatalytic CO2 reduction to CO with a Faradaic efficiency of about 50% and a turnover frequency (TOF) of 4.4 s−1, whereas complex 2 can perform electrocatalytic of CO2 reduction with a Faraday efficiency of ~22% and a TOF of 0.3 S−1. The electrocatalytic CO2 reduction selectivity and activity of the two complexes are poor when the solvent is changed to THF. Combined with the results of the density functional theory calculation, we propose that the binding pattern of the redox‐active ligand OMePDI has a significant effect on the electrocatalytic activity for the two Ru(II)PDI complexes. The effect of PDI binding pattern on the electrocatalytic activity of CO2 reduction mediated by Ru(II)PDI 1 and 2 has been investigated. Compared with complex 2, PDI ligand in complex 1 with the aromatized tridentate ŋ3‐N,N,N‐coordinatedmode can store multiple electrons in its large delocalized Π systems, cooperating with the central Ru(II) ion for electrocatalytic reduction CO2 to CO with a high selectivity, a Faraday efficiency of about 50% and TOF of 4.4 s‐1 in MeCN solution.