Carbohydrate phosphinites as chiral ligands for asymmetric synthesis catalyzed by complexes : V. New rhodium(I)-chelates prepared by precipitation from the equilibrium between neutral and cationic complexes and hydrolysis of their bonded ligands

Some byproducts of the preparation of cationic rhodium(I)bis(phosphinite)-chelates 3 from rhodium(I)-[(Z,Z)-cycloocta-1,5-diene]-acetylacetonate, 4,6-O-alkylidene-glucopyranoside-2,3-O-bisphosphinite 1, such as ligand and acid HA can be isolated. Neutral bis(phosphinite)complexes 2 having acetylacetonate as chelating anion and being inactive to hydrogenation, are separated from the equilibrium with cationic complexes 3 by precipitation using polar solvents. The acids, HA, as catalysts for solvolysis give the new cationic chelates 4 in a prolonged reaction. The chelates 4 exhibit excellent catalytic properties in asymmetric hydrogenation and possess free hydroxy groups in the 4,6 positions of the carbohydrate ligand.