Electronic Tuning of Copper(II) Imidazole‐Benzimidazole Complexes for Efficient and Selective Oxygen Reduction Reaction

Abstract A series of nature‐inspired copper(II) complexes with electronically tunable imidazole‐benzimidazole (ImBenz) ligands, including Cu( ImBenz‐H )Cl 2 , Cu( ImBenz‐NO 2 )Cl 2 , and Cu( ImBenz‐OCH 3 )Cl 2 , was designed to probe the cooperative influence of redox‐active ligands and metal centers on oxygen reduction reaction (ORR) activity. Single‐crystal X‐ray diffraction results for all three complexes confirm a distorted square planar geometry (τ 4 = 0.11–0.20). Electrochemical studies and rotating ring‐disk electrode (RRDE) experiments in neutral aqueous electrolyte revealed that Cu( ImBenz‐NO 2 )Cl 2 bearing an electron‐withdrawing group on the benzimidazole ring exhibited high selectivity for the 4‐electron reduction of O 2 to H 2 O, with the number of electrons transferred ( n ) of 3.8, yielding ∼14% H 2 O 2 . Cu( ImBenz‐H )Cl 2 favored the 2‐electron reduction of O 2 to H 2 O 2 , producing the highest H 2 O 2 yield (∼37%). In contrast, Cu( ImBenz‐OCH 3 )Cl 2 showed the mixed 2‐ and 4‐electron ORR pathways. Foot‐of‐the‐wave analysis (FOWA) revealed turnover frequencies of 10 2 s −1 for the catalysts with catalytic rates and product selectivity strongly influenced by the redox‐active ligand structure. These results demonstrate that the systematic electronic modification of the ligand with Cu(II) metal center is a powerful strategy for tuning ORR activity and selectivity, underscoring the potential of earth‐abundant copper complexes for future clean energy applications.