Defining the Structure and Reactivity of Benzoate-Ligated Ce(IV)-Alkoxide Complexes in LMCT Photocatalysis

Cerium(IV) ligand-to-metal charge transfer (LMCT) photocatalysis has emerged as a powerful strategy for generating open-shell intermediates through photoinduced bond homolysis. However, the precise structure and reactivity of putative heteroleptic Ce(IV)-alkoxide intermediates involved in these processes remain poorly understood, limiting mechanistic insight into how the ligand environment controls LMCT reactivity. Herein, we report the identification, isolation, and characterization of a family of benzoate-ligated Ce(IV)-alkoxide complexes [(RL)4CeIV(X)][NEt4] (RL = 4-substituted 2,6-diisopropylbenzoate; R = OMe, iPr, CF3, X = OMe, Cl). Their solution dynamics, photochemical, electrochemical, and catalytic behavior were systematically investigated. Under blue-light irradiation, [(iPrL)4CeIV(OCH3)][NEt4] undergoes selective Ce–O bond homolysis to form [(iPrL)4CeIII][NEt4] and the methoxy radical, providing direct experimental insight into the reactivity of photoactive Ce(IV)-alkoxide species. The impact of benzoate ligation was further evaluated in the dehydroxymethylative alkylation of cyclohexylmethanol with electron-poor olefins. Benzoate ligation significantly enhances catalytic efficiency and selectivity by suppressing competing chloride-derived reactivity responsible for side-product formation. Kinetic studies further indicate that benzoate ligands do not primarily prevent catalyst decomposition but instead modulate the cerium coordination environment, thereby biasing the accessible LMCT reactivity manifold toward productive Ce–O bond activation. These findings provide rare molecular-level insight into benzoate-controlled cerium LMCT photocatalysis and establish coordination sphere modulation as a key strategy for controlling reactivity in LMCT systems.