Diastereomeric diphosphites (L∩L ) 3-8) have been synthesized from enantiomerically pure pentane-2,4-diol and axially chiral 3,3′-bis(trialkylsilyl)-2,2′-bisphenol phosphorochloridites and 3,3′-bis(trialkylsilyl)-2,2′-bisnaphthol phosphorochloridites. These diphosphites have been used to test the influence of chiral cooperativity in the rhodium-catalyzed asymmetric hydroformylation of styrene. Systematic variation in chirality at both the chiral ligand bridge and the axially chiral biphenyl and binaphthyl substituents revealed a remarkable effect on the selectivity of the hydroformylation catalysts. For the atropisomeric bisnaphthol-based diphosphites, cooperative effects were observed in the asymmetric hydroformylation of styrene. High enantioselectivities (87%) and regioselectivities up to 95% for 2-phenylpropanal were found under mild reaction conditions (15-50°C, 20 bar of syn gas CO-H 2 [1:1]) for the ligand derived from (2R,4R)-pentane-2,4-diol and (S)-bisnaphthol. The same high enantiomeric excess was observed for the free-rotating bisphenol-substituted ligands. The highest selectivity was obtained with trimethylsilyl substituents at the ortho position. The solution structures of the active catalysts [HRhL∩L-(CO) 2 complexes (L∩L ) 3-8)], have been studied by 31 P and 1 H NMR spectroscopy at variable temperature (313-213 K). Spectroscopic data, in combination with the obtained results in catalysis, suggest that diphosphite ligands (L∩L) containing the conformationally flexible axially chiral biphenyl moieties predominantly exist as single atropisomers in the HRhL∩L-(CO) 2 complexes. Comparison of the bisphenol and bisnaphthol substituents suggests that the high enantiomeric excesses obtained with the former are caused by the preferential formation of the most selective diastereomer.

Chiral diphosphite ligands (PP) prepared from {(2,2'-biphenyl-l,l'-diyl), (4,4',6,6'-tetra-t-butyl-2,2'-biphenyl-l,l'-diyl), 4,4'-di-t-butyl-6,6'-dimethoxy-2,2'-biphenyl-l,l'-diyl) and di(2-t-butyl, 6-methylphenyl)}

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Palladium(0)-Mediated Coupling of Bromophosphaalkenes with Grignard Reagents.-New isomerically pure (E)-phosphaalkenes are obtained from the reaction of monobromophosphaalkenes (I) and (IV) with Grignard reagents by Pd (0)-catalyzed Stille-type reaction. The result with the ( Z)-isomer (IV) is unexpected. In all cases isomerization occurs to give the (E)-product. -(VAN DER SLUIS, M.; KLOOTWIJK, A.; WIT, J. B. M.; BICKELHAUPT, F.; VELDMAN, N.; SPEK, A. L.; JOLLY. P. W.; J.