Asymmetric catalysis, chiral sulfonated phosphines

Water-soluble mono- and diphosphines represent the major class of phosphines used in aqueous-phase homogeneous catalysis. However, some new types of water-soluble phosphines have been developed, including phosphines containing sugar substructures [31] or phosphonate chains [32], and chiral sulfonated phosphines for the asymmetric hydrogenation of dehydropeptides [33] and phosphines with amino acid moieties [59]. 

A number of chiral bisphosphines related to DiPAMP(l) were prepared and evaluated in asymmetric catalysis. Many variants were closely equivalent but none were superior to the parent compound. In addition, some monophosphines containing sulfone substituents were quite effective. These had the particular advantage of being usable in water solution. Several new DIOP derivatives were tried in the hydroformylation of vinyl acetate but only modest enantiomeric excesses were achieved. A 72% enantiomeric excess was achieved on dehydrovaline under relatively forcing conditions using DiCAMP(3). This result was remarkable since these phosphine ligands generally work very poorly, if at all, on tetrasubstituted olefins. 

Di)phosphines containing chiral backbones equipped with diphenylphosphino-substituents are the most successful and best-investigated chiral ligands in asymmetric homogeneous catalysis. Thus, a variety of chiral water-soluble ligands were prepared by direct sulfonation of these phosphorus ligands under conditions similar to those for the synthesis of achiral sulfonated phosphines. 

Stelzer and co-workers reported a number of chiral water-soluble secondary phosphines [14], prepared by nucleophilic phosphination of primary phosphines with fluorinated aryl sulfonates in the superbasic medium DMSO/KOH. Further reaction with alkyl halides gives bidentate tertiary phosphines with P-chirality, but only racemic versions have been reported so far. Hanson et al. introduced so-called surface-active phosphines into asymmetric aqueous-phase catalysis. One of the main problems inherent to two-phase catalysis is the often very low miscibility of the substrates in the aqueous phase. Insertion of long alkyl chains between phosphorus atoms and phenyl groups in sulfonated phosphine ligands has been proven to increase reaction rates in the Rh-catalyzed hydroformylation of 1-octene [15], This concept was extended to a number of chiral ligands, i.e., the monoden-... 

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