Synthesis of Water-soluble Phosphines Having Polyether Substituents and Their Application to Transition Metal-catalyzed Water Gas Shift Reaction

Abstract

For the purpose of eliminating the disadvantages of hydrophobic transition metal catalysts, the water-soluble phosphines, P[CHR(CH₂CH₂O)_nCH₃]₃(R=H, CH₃ n=1, 2, 3, ), having chemically stable side chains were synthesized. Their hydrophilicities were correlated with the number of the oxygen atom in the molecules on the basis of the measurements of the solubility in water and the distribution equilibrium between aqueous and organic phases. The usefulness of the phosphines as ligands for metal-catalyzed reactions in aqueous solution was studied in the water gas shift reaction under strong basic conditions as a model. The catalyst of W(CO)₆-L(L=water-soluble phosphine) showed high activity in aqueous solution, and the active species were proved to be water-soluble complexes, cis- and trans-W(CO)₄L₂. A catalyst system, [RhCl(cod)]₂-L, was effecient not only in aqueous solution but also under aqueous-organic two-phase conditions. The catalytic activity in the latter case was correlated with the distribution constant of the phosphine ligands. These facts suggest that the catalysis is attributed to the phosphine complex in aqueous phase. The rhodium-catalyzed hydroformylation of olefins with CO and H₂O could also be achieved under two-phase conditions. This reaction system had the advantage of simplifying the process of separating the catalyst from the organic products.