Tunable electrochemical oxidation of bisphosphines: a general strategy for selective synthesis of bidentate phosphine mono- and dioxides

Abstract

Bidentate phosphine monooxides (BPMOs), characterized by their semi-tunable coordination behavior, are privileged scaffolds in catalysis, yet their synthetic accessibility remains a significant challenge due to the difficulty in achieving selective mono-oxidation of bisphosphines. Herein, we report a novel, tunable electrochemical strategy for the selective synthesis of BPMOs and bisphosphine dioxides (BPDOs) without the need for metal catalysts or stoichiometric oxidants. By simply modulating the applied current in a nickel electrode system using tetramethylammonium iodide as a redox mediator and DMF as both the solvent and oxygen source, we achieve remarkable control over the oxidation pathway. Lower currents (e.g., 6 mA) favor the selective formation of BPMOs, while higher currents (e.g., 10 mA) promote the synthesis of BPDOs. This protocol demonstrates broad substrate scope across various bisphosphine skeletons with different linker lengths and can be successfully scaled up to gram-scale. Notably, this method exhibits good faradaic efficiency (up to 62.8% and 63.7% for gram-scale mono- and di-oxidation, respectively), highlighting its energy efficiency. Mechanistic studies, including control experiments and cyclic voltammetry, confirm DMF as the oxygen source and elucidate the role of the iodide mediator. This electrochemical method offers an operationally simple, cost-effective, and environmentally benign platform for the green synthesis of these valuable ligands.