NEW HYDROFORMYLATION RHODIUM CATALYSTS WITH DITHIOLATE CHIRAL LIGANDS

Asymmetric hydroformylation of styrene is performed using the bridge dithiolate chiral rhodium complexes [Rh-2(mu-(-)-DIOS) (cod)(2)](n) n = 2 (1) and n = 1 (2); ((-)-DIOS: 2,3-O-isopropylidene-1,4-dithio-L-threitol and cod: 1,5-cyclooctadiene) as catalyst precursors. The catalytic system 1 provides high conversion in the corresponding aldehydes (100% at 30 bar, 65 degrees C) with a selectivity in 2-phenylpropanal of 64%. Addition of PPh(3) to the catalytic system 1 increases the selectivity in 2-phenylpropanal to 91% in the same conditions. Although the ee's obtained using 1 were low (3-5%), the addition of a chiral phosphine, (+)-DIOP ((2S,3S)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino) butane), improves the ee in (S)-2-phenylpropanal to 17%. However the addition of (-)-DIOP gives a lower ee (3% (S)). Comparative results were obtained using 2 as catalyst precursor indicating that similar species were formed during catalytic cycle.