[224618-29-5]  · C11H26P2  · (220.27)

(a chiral ligand for transition metal-catalyzed asymmetric reactions)

Alternate Name: MiniPHOS.

Physical Data: colorless oil.

Solubility: soluble most organic solvents.

Preparative Methods: phosphorus trichloride is allowed to react sequentially with alkylmagnesium chloride, methylmagnesium bromide, and BH3-THF complex in THF to give alkyldimethylphosphine-borane. The phosphine-borane so obtained is enantioselectively deprotonated by s-BuLi in the presence of (-)-sparteine in Et2O at -78 to -50°C, followed by treatment with alkyldichlorophosphine, methylmagnesium bromide, and BH3-THF complex to give a MiniPHOS-borane complex as a diastereomixture. After removal of the meso-isomer by silica gel chromatography, the enantiomerically pure product is obtained by recrystallization from methanol or ethanol. The boranato group is removed by reaction with trifluoromethanesulfonic acid in toluene, followed by treatment with aqueous KOH to give the desired diphosphine 1 (eq 1).

Purification: filtered through Al2O3 with Et2O elution under N2 or Ar atmosphere.

Handling, Storage, and Precautions: stench. Undergoes oxidation to the phosphine oxide on standing in air. Usually prepared before use by deboranation of the air stable phosphine-borane.

Rhodium-Catalyzed Asymmetric Hydrogenation of Olefins.

MiniPHOS (1) can be used in rhodium-catalyzed asymmetric hydrogenation of olefinic compounds.1 The complexation with rhodium is carried out by treatment of 1 with [Rh(nbd)2]BF4in THF (eq 2). The hydrogenation of a-(acylamino)acrylic derivatives proceeds at room temperature and an initial H2 pressure of 1 or 6 atm in the presence of the 0.2 mol% MiniPHOS-Rh complex 2. The reactions are complete within 24-48 h to afford almost enantiomerically pure a-amino acids (eq 3). Itaconic acids,2 enamides,3 and dehydro-b-amino acids4 can also be hydrogenated with excellent enantioselectivity (eq 4-6).

Rhodium-Catalyzed Asymmetric Hydrosilylation of Ketones

Complex 2 is a good catalyst for catalytic asymmetric hydrosilylation of ketones (eq 7).1 The reactions are carried out by using 1-naphthylphenylsilane at -40°C in THF in the presence of 2 (1 mol%) for 3-4 days. Several types of ketones are hydrosilylated to afford optically active alcohols after acidic work-up.

Related Reagents.


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9. (a) Scott, J. W.; Keith, D. D.; Nix Jr, G.; Parrish, D. R.; Remington, S.; Roth, G. P.; Townsend, J. M.; Valentine Jr, D.; Yang, R., J. Org. Chem. 1981, 46, 5086. (b) Knowles, W. S., Acc. Chem. Res. 1983, 16, 106.
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12. Pye, P. J.; Rossen, K.; Reamer, R. A.; Tsou, N. N.; Volante, R. P.; Reider, P. J., J. Am. Chem. Soc. 1997, 119, 6207.

Hiroshi Danjo & Tsuneo Imamoto

Chiba University, Chiba, Japan

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.