Thiophene-Based Bidentate Phosphine Ligands for Aqueous Chemistry: Synthesis, Rhodium Complexation, and Electrochemical Properties

Aqueous-phase coordination chemistry can enable greener synthetic methods, but complex design remains constrained by the narrow scope of ligands that operate effectively in water. Herein, we report a modular synthetic pathway to access a new family of air- and water-stable thiophene-based bidentate phosphine ligands bearing hydroxyl and amino substituents. Their solubility, complexation behavior, and electrochemical properties were evaluated through the synthesis and characterization of the corresponding rhodium complexes. The hydroxyl-functionalized complex is insoluble in water, whereas the amine analogue displays pH-dependent solubility. Methylation of the amine derivative affords an ammonium ligand, and the resultant rhodium complex is soluble across a broad range of pH conditions. Electrochemical studies reveal that the amino and hydroxyl complexes undergo reversible two-electron reductions in acetonitrile, in contrast to the ammonium complex, which exhibits an irreversible feature. The synthetic methods described expand the toolkit for water-compatible coordination chemistry and provide a foundation for future applications in aqueous-phase catalysis.