Syntheses of water-soluble N-donor ligands for aqueous catalysis using green, Michael-type addition reactions

Abstract

A new route for synthesizing sulfonate-containing N-donor ligands has been developed involving the Michael-type addition reaction of primary or secondary amines with sodium vinylsulfonate in water. Our reactions offer several advantages over traditional Michael-type addition reactions. For example, while most conjugate addition reactions are carried out in organic solvents in the presence of bases or acids (S. G. Davies, T. D. McCarthy, Synlett, 1995, 700–704; D. Rosenthal, G. Braundrup, K. H. Davies, M.E. Wall, J. Org. Chem., 1965, 30, 3689–3696), our reactions adhere to green chemistry principles and are conducted in aqueous solutions without harsh bases or acids, eliminating the need for more toxic compounds and solvents. Additionally, the new synthetic route utilizes selective conjugate addition reactions instead of unselective alkylation reactions using sodium 2-bromoethanesulfonate or similar sulfonated alkyl halides (J. March, Advanced Organic Chemistry: reactions, mechanisms and structure, Wiley, New York, 4th edn., 1992, pp. 411-413), which greatly decreases the amount of undesired side-products. Finally, the new synthetic route yields new, water-soluble ligands which may be utilized in aqueous catalysis involving water-soluble metal complexes.