Phosphanorbornadienephosphonates as a new type of water-soluble phosphines for biphasic catalysis

The reaction of (phenylethynyl)phosphonates or- phosphonamides with 1-phenyl-3,4-dimethylphosphole at 140 degrees C affords the corresponding alpha-P(O)-substituted 1-phosphanorbornadienes (1-3). The corresponding PO3Na2 salt (5) displays some solubility in water (20 g/L) but is a poor ligand both for the rhodium-catalyzed hydrogenation and hydroformylation of olefinic bonds. The reaction of an unsubstituted ethynylphosphonamide with the same phosphole yields a 3:1 mixture of alpha- and beta-P(O)-substituted 1-phosphanorbornadienes 7 and 8. The beta-PO3Na2 salt (10) is a good ligand for the hydrogenation of (Z)-alpha-(N-acetamido)cinnamic acid and displays a high solubility in water (230 g/L). The chelation of rhodium by the alpha-P(O)-substituted 1-phosphanorbornadienes probably explains the loss of hydrogenation efficiency for [RhL(2)](+) when L = 5.