Aerobic Synthesis of Zinc Organophosphate Complexes from Elemental Zinc: Enabling Phosphoric Acid Diester-Based Catalysis for O2-Mediated Baeyer-Villiger Oxidation

Abstract

We report the first aerobic synthesis of zinc organophosphate complexes, Zn[O₂P(OR)₂]₂, from inexpensive elemental zinc (Zn(0)) and structurally diverse phosphoric acid diesters (PADs) under ambient conditions. This mild and operationally simple method contrasts with conventional approaches that rely on elevated temperatures, high pressures, or costly zinc salts. The transformation accommodates a broad range of PADs, providing access to various zinc complexes in high yields with diverse steric and electronic properties. Mechanistic studies suggest that the reaction proceeds via a single-electron transfer from Zn(0) to PAD, followed by the activation of O₂ to form a reactive peroxy intermediate. The resulting Zn[O₂P(OR)₂]₂ thus obtained—and PADs regenerated through hydrolysis—function as molecular catalysts for aerobic Baeyer-Villiger oxidation of cyclobutanones, operating under near-ambient conditions without any stoichiometric peroxide oxidants. The system proceeds through a PAD-mediated catalytic cycle, exhibiting high chemoselectivity and regiodivergent behavior reminiscent of enzymatic oxidations. Notably, this represents the first example of a non-biomimetic, PAD-catalyzed Baeyer-Villiger oxidation using O₂ as the terminal oxidant. Preliminary results with chiral PADs also demonstrate the feasibility of enantioselective variants. Together, these findings establish a versatile strategy for accessing structurally tunable zinc complexes and expanding the scope of aerobic oxidation catalysis beyond traditional systems.