INFLUENCE OF THE REACTION TEMPERATURE ON THE ENANTIOSELECTION OF STYRENE HYDROFORMYLATION CATALYZED BY PTCL(SNCL3) COMPLEXES OF P-ARYL-SUBSTITUTED CHIRAL LIGANDS

The asymmetric hydroformylation of styrene catalyzed by PtCl(SnCl3) complexes of (-)(2S,4S)-2,4-bis[bis(p-(dimethylamino)phenyl)phosphino]pentane (1), (-)(2S,3S)-2,3-O-isopro-pylidene-2,3-dihydroxy-1,4-bis[bis(p-(dimethylamino)phenyl)phosphino]butane (2), and (-)-(2S,3S)-2,3-bis[bis(p-(dimethylamino)phenyl)phosphino]butane (3) is strongly temperature dependent. With 1 and 2 as the catalysts a reversal in the prevailing product configuration occurs at relatively low temperatures (53 and 72-degrees-C, respectively). 1 provides good enantioselectivities in both directions, 56.7 % ee in the R product at 100-degrees-C and 60.6 % ee in the S product at 30-degrees-C. The variation of enantioselectivity with temperature is consistent with competing reaction pathways via diastereomeric intermediates of a single chelate conformation.