Accelerated Biphasic Hydroformylation by Vesicle Formation of Amphiphilic Diphosphines

Abstract

The synthesis, aggregation behavior, and catalytic activity of rhodium complexes of a series of Xantphos derivatives with surface-active pendant groups, −4-C6H4O(CH2)nC6H4(SO3Na)− (n = 0, 3, 6) is described. Electron microscopy experiments show that these ligands and their complexes form vesicles in water if the hydrophobic part of the ligand is large enough (n = 3, 6). The formed aggregates are stable at elevated temperatures (90 °C), and their presence leads to a significant enhancement of the solubility of organic substrates in aqueous solution. This enhanced solubility results directly in a higher reaction rate in the rhodium-catalyzed hydroformylation of 1-octene. Furthermore, recycling experiments show that the TOF and the high selectivity toward the more valuable linear aldehyde remains approximately the same in four consecutive runs. This indicates that the aggregates stay intact during the recycling and the active rhodium complex is retained in the water-phase quantitatively.