Synthesis of 4-sulfonatobenzylphosphines and their application in aqueous-phase palladium-catalyzed cross-coupling

Abstract Aqueous-biphasic catalysis offers the potential for safer and more environmentally sustainable synthetic processes. In addition, hydrophilic supporting ligands allow homogeneous catalysts to be readily separated from organic products and potentially reused. The synthesis of two new water-soluble ligand precursors, di- tert -butyl(4-sulfonatobenzyl)phosphonium and di-1-adamantyl(4-sulfonatobenzyl)phosphonium, are reported. The air-stable, zwitterionic phosphonium salts were prepared by the reaction of dialkylphosphines with ethyl 4-bromomethylbenzenesulfonate, which results in a one-pot alkylation followed by deprotection of the ethyl sulfonate. This methodology provides an operationally simpler route to sulfonated benzylphosphines than electrophilic sulfonation. The new phosphine ligands were applied to aqueous-phase Suzuki and Sonogashira couplings of aryl bromides.