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

• A one pot method to synthesize 4-sulfonatobenzylphosphines from ethyl 4-(bromomethyl)benzenesulfonate is reported.
• The zwitterionic phosphonium sulfonate preligands have been structurally characterized.
• Ligands provide effective catalysts for aqueous-phase Suzuki and Sonogashira couplings of aryl bromides.

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.

A novel one-pot alkylation/deprotection approach to the synthesis of zwitterionic benzylphosphonium sulfonate ligands is reported. The resulting ligands provide effective catalysts for the Suzuki and Sonogashira coupling of aryl bromides in water or water/organic solvent systems.Figure optionsDownload as PowerPoint slide