Asymmetric hydroformylation of styrene catalyzed by platinum complexes of chiral diphosphites with atropisomeric terminal moieties

To study the nature of steric and electronic effects of diphosphites, a novel diphosphite was synthesized and tested with regard of its catalytic performance in the hydroformylation of styrene catalyzed by platinum complexes. The novel ligand 3 was prepared by the reaction of enantiomerically pure pentane-2,4-diol with (S)-2-chloro-5,5',6,6',7,7',8,8'-octahydro-dinaphtho[2,1-d:1',2'-f][1,3,2]dioxaphosphepine based on H-8-BINOL (H-8-BINOL = 5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol). For a comparative study, the BINOL (1,1'-bi-2-naphthol) based analogue 4 of 3 has also been synthesized. The highest chemoselectivity to aldehyde (71%) and regioselectivity to branched aldehyde (85%) with an enantiomer excess (ee) of 86% was obtained with the platinum(II)-SnCl2 catalytic system associated with (2S,4S)-bis(S)-3.