Beyond TPPTS: New approaches to the development of efficient palladium-catalyzed aqueous-phase cross-coupling reactions

Water is an attractive solvent for metal-catalyzed reactions with both economic and environmental sustainability benefits. In addition, the use of a hydrophilic catalyst in an aqueous-biphasic solvent system provides the opportunity to easily recover, and potentially recycle, the catalyst species. The feasibility of cross-coupling reactions catalyzed by hydrophilic palladium catalysts was first demonstrated using sulfonated analogs of tripbenylpbosphane, such as tris(3-sulfonatophenyl)phosphane trisodium salt (TPPTS). Catalysts derived from TPPTS and other structurally similar hydrophilic phosphanes are generally effective only with aryl iodides and activated aryl bromides. This microreview will focus on more recently developed hydrophilic ligands with increased steric demand and electron-donating abilities that are effective in coupling reactions of aryl bromides and chlorides under mild conditions in aqueous solvents. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheira, Germany, 2006).