(1,5-Cyclooctadiene)[(3R,4R)-3,4-bis(diphenylphosphino)-1-methylpyrrolidine]rhodium Tetrafluoroborate1

[100366-06-1]  · C37H41BF4NP2Rh  · (1,5-Cyclooctadiene)[(3R,4R)-3,4-bis(diphenylphosphino)-1-methylpyrrolidine]rhodium Tetrafluoroborate  · (MW 737.39)

(catalyst for asymmetric hydrogenation of a-acylaminoacrylic acid derivatives2)

Solubility: insol ether; sol CH2Cl2, MeOH

Analysis of Reagent Purity: 31P NMR (CD2Cl2): d 33.17 (d, 2JRh,P = 148.2 Hz).

Preparative Methods: the ligand (3R,4R)-3,4-bis(diphenylphosphino)-1-methylpyrrolidine (1a) is prepared from L-tartaric acid via (3R,4R)-3,4-bis(diphenylphosphino)-1-benzylpyrrolidine (1b) as shown in eq 1. The title cationic rhodium complex is made by mixing bis(1,5-cyclopentadiene)rhodium tetrafluoroborate and (1a) in CH2Cl2 under nitrogen.

Asymmetric Hydrogenation Catalyst.

Since catalytic asymmetric hydrogenation of a-acylaminoacrylic acid derivatives is an important process to afford a-amino acid derivatives, many rhodium complexes possessing optically active phosphine ligands have been developed in last two decades.3-7 [Rh{(R)-(1a)}(cod)]BF4 (2a) is one of the most efficient catalysts for this purpose with respect to activity and enantioselectivity. Besides (2a), several derivatives, which have various substituents on the nitrogen atom of the pyrrolidine ring, will be mentioned below.

a-(Acetylamino)cinnamic acid derivatives (3) are hydrogenated in the presence of (2), which are derived from natural L-tartaric acid, to afford natural (S)-N-acetylphenylalanine derivatives with high enantioselectivity (eq 1).8 Some examples are shown in Table 1. Less than 0.01 mol % of catalyst is needed to complete the reaction under mild conditions with high enantioselectivity. The substituents on the nitrogen atom of (2) have no marked influence on the catalytic activity or the selectivity. This reaction is also insensitive to the variation of substituents on the phenyl ring of (3).

Water-soluble (1,5-cyclooctadiene)[(3R,4R)-3,4-bis(diphenylphosphino)-1,1-dimethylpyrrolidinium]rhodium bis(tetrafluoroborate) (4) catalyzes the hydrogenation of the sodium salt of a-(acetylamino)cinnamic acid to afford the (S)-acetylphenylalanine sodium salt in 90% ee at 22 °C.9

A silica-supported rhodium complex of (3R,4R)-3,4-bis(diphenylphosphino)pyrrolidine (5) is also an effective catalyst.10 This heterogeneous catalyst mediates asymmetric hydrogenation of (3a) as well as its methyl ester in comparable selectivities to the homogeneous one shown above.

Related Reagents.

Bis(bicyclo[2.2.1]hepta-2,5-diene)rhodium Perchlorate; Bis(bicyclo[2.2.1]hepta-2,5-diene)rhodium Perchlorate-(R)-1-(S)-1,2-Bis(diphenylphosphino)ferrocenylethanol; Bis(1,5-cyclooctadiene)rhodium Tetrafluoroborate-(R)-2,2-Bis(diphenylphosphino)-1,1-binaphthyl.

1. (a) Takaya, H.; Noyori, R. COS 1991, 8, Chapter 3.2. (b) Noyori, R.; Kitamura, M. In Modern Synthetic Methods; Sheffold, R. Ed.; Springer: Berlin, 1989; Vol. 5, p 115.
2. Nagel, U.; Kinzel, E. CB 1986, 119, 1731.
3. Knowles, W. S.; Sabacky, M. J. CC 1968, 1445.
4. Horner, L.; Siegel, H.; Büthe, H. AG(E) 1968, 7, 942.
5. Kagan, H. B.; Dang, T. P. JACS 1972, 94, 6429.
6. Miyashita, A.; Takaya, H.; Souchi, T.; Noyori, R. T 1984, 40, 1245.
7. Burk, M. J. JACS 1991, 113, 8518.
8. Nagel, U. AG(E) 1984, 23, 435; AG 1984, 96, 425.
9. Nagel, U.; Kinzel, E.; Andrade, J.; Prescher, G. CB 1986, 119, 3326.
10. Nagel, U.; Kinzel, E. CC 1986, 1098.

Yoshihiko Ito & Michinori Suginome

Kyoto University, Japan

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