Water-soluble organometallic catalysts from carbohydrates. 2. A strategy for the preparation of catalysts with pendant quaternary ammonium groups using D-salicin

A series of water-soluble chelating bis-phosphinite ligands have been prepa red from D-salicin (2-(hydroxymethyl)phenyl beta -D-glucopyranoside The 4- and 6-hydroxyl groups of salicin were protected as a cyclic ketal. Mitsunob u reaction with phthalimide at the benzylic position-was used to install th e aminomethyl side-chain in the C-1-aromatic substituent; Formation:of the bis-2,3-O-diarylphosphinite was accomplished by reaction of the resulting d iol with chlorodiarylphosphine. Quaternization with Meerwein's salt (Me3OBF4-) followed by reaction with Rh+(COD)(2) BF4- gave precatalysts with lim ited aqueous solubility. Deprotection of the ketal group with acidic resin in methanal gave water-soluble cationic Rh complexes that-are competent to carry out highly efficient hydrogenation of acetamidoacrylic acid derivativ es in organic, aqueous, or biphasic media. However, enantioselectivities of these reactions in neat aqueous or biphasic media are generally lower than those observed in organic medium.