Harnessing Benzoyl-Urea Secondary-Sphere Hydrogen-Bonding to Enhance Oxygen Evolution Catalysis by Cobalt Corroles

Secondary-sphere control is leveraged to boost cobalt corrole oxygen-evolution catalysis. We install a pendant benzoyl-urea unit on a corrole scaffold to position a hydrogen-bond donor above the metal site. The ligand is obtained via an isolable N-benzoyl-dicyclohexylurea intermediate, converted to the FB corrole, and metalated to Co(III); a pentafluorophenyl analog lacking the urea serves as control. X-ray/time-dependent density functional theory (TD-DFT) show axial pyridine ligation lifts the pendant carbonyl toward the catalytic pocket with reduced saddling. In MeCN, CV features reversible Co (III/II) couples at -0.62 V (urea) and -0.52 V (control) versus FeCp₂ ^+/0, plus ligand-centered oxidations; spectro-electrochemistry/EPR (g _iso = 1.9986) confirm a corrole-radical [Co^III(corrole^•2-)(py)₂]⁺. Water addition unveils catalytic waves ~1.12V(urea) and 1.21 V (control), versus FeCp₂ ^+/0. Under CPE (1.78 V, vs. Ag/AgCl), the urea-bearing complex delivers 83.9% Faradaic efficiency, TOF 1.19 s^-1 (vs. 59.6%, 0.47 s^-1 for control); a KIE = 1.3 implicates PCET. DFT supports WNA at a Co-oxyl, [Co^III(corrole^•2-)(O^•-)(py)], with the pendant carbonyl H-bonding to the incoming H₂O (O···H = 1.71 Å), thereby lowering the activation barrier relative to a truncated analog. These results establish benzoyl-urea secondary-sphere engineering as a concise, general strategy to enhance charge utilization and O-O bond formation in cobalt corrole oxygen evolution reaction catalysis.