Influence of degree of sulfonation of BDPP upon enantioselectivity in rhodium-BDPP catalyzed hydrogenation reactions in a two phase system
✍ Scribed by Cornelis Lensink; Evelien Rijnberg; Johannes G. de Vries
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 672 KB
- Volume
- 116
- Category
- Article
- ISSN
- 1381-1169
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✦ Synopsis
Asymmetric hydrogenation experiments were carried out with catalysts prepared in situ from [Rh(COD)CI], and 2 eq. of a sulfonated (2S,4S)-bis-2,4-(diphenylphosphino)pentane carrying O-4 sulfonate groups, in a two phase aqueous organic system. The effect of degree of sulfonation on enantioselectivity was determined in the hydrogenation of one imine and three olefin substrates. In the hydrogenation of the substrates N-benzylacetophenoneimine (2) and dimethyl itaconate (8) the monosulfonated ligand lb was by far superior; hydrogenation using this ligand proceeded with 94% and 28% ee, respectively, whereas use of bis-or trissulfonated ligand gave practically racemic product. In the hydrogenation of N-acetamidocinnamic acid (4) or methyl ester (6) enantioselectivity decreased with degree of sulfonation. The mono sulfonation effect is not due to steric or electronic reasons, nor is an anion effect involved.