Bis(1,5-cyclooctadiene)rhodium Tetrafluoroborate-(R)-2,2-Bis(diphenylphosphino)-1,1-binaphthyl1


[35138-22-8]  · C16H24BF4Rh  · Bis(1,5-cyclooctadiene)rhodium Tetrafluoroborate-(R)-2,2-Bis(diphenylphosphino)-1,1-binaphthyl  · (MW 406.07) ((R)-BINAP)

[76189-55-4]  · C44H32P2  · Bis(1,5-cyclooctadiene)rhodium Tetrafluoroborate-(R)-2,2-Bis(diphenylphosphino)-1,1-binaphthyl  · (MW 622.68)

(catalyst for asymmetric hydrogenation,2 isomerization,3 hydroboration,4 and intramolecular hydrosilation5 of alkenes)

Physical Data: [Rh(cod)2]BF4: mp 206-8 °C; (R)-BINAP: mp 240-241 °C; [a]25D + 229° (c = 0.32, benzene).

Form Supplied in: [Rh(cod)2]BF4: orange-red crystals; (R)-BINAP: colorless crystals.

Analysis of Reagent Purity: (R)-BINAP: 31P NMR (4:1 C6D6-CD3OD): d -12.8 (s); mp and optical rotation shown above are also useful for analysis of the purity.

Purification: [Rh(cod)2]BF4: recrystallization from CH2Cl2 and ether; (R)-BINAP: recrystallization from a mixture of toluene and EtOH.

Handling, Storage, and Precautions: [Rh(cod)2]BF4: hygroscopic; corrosive.

Asymmetric Hydrogenation.

The diene-free cationic rhodium complex of (R)-BINAP catalyzes the enantioselective hydrogenation of dehydroamino acids. a-(Benzoylamino)acrylic acid is hydrogenated at rt to afford (S)-N-benzoylphenylalanine in 100% ee (eq 1).2 To obtain maximal stereoselectivity the reaction should be carried out under a low concentration of substrate (100% in 0.013 M vs. 62% in 0.15 M) and low initial hydrogen pressure (100% at 1 atm, but 71% at 50 atm).

Optically active homoallylic alcohols are hydrogenated with differentiation of the diastereofaces (eq 2).6 Use of the matched ligand, i.e. (R)-BINAP, gives a product of 96% de, while the mismatched (S)-ligand affords low selectivity.

Allylic Hydrogen Migration.

Cationic RhI diphosphine complexes are very active catalysts for allylic hydrogen migration of tertiary and secondary allylamines to give the corresponding (E)-enamines and imines, respectively. Highly enantioselective isomerization is accomplished by use of (R)-BINAP as a diphosphine ligand.3 Diethylnerylamine, which has (Z) geometry, gives (R)-(E)-diethylcitronellenamine in 95% ee in the presence of 1 mol % of [Rh{(R)-BINAP}(cod)]ClO4, while the isomeric diethylgeranylamine gives (S)-(E)-diethylcitronellenamine in 96% ee (eq 3). Thus the method presented above offers a desired enantiomer by proper choice of alkene geometry and chirality of BINAP.

Cationic Rh-(R)-BINAP complexes also catalyze the allylic hydrogen migration of racemic 4-hydroxy-2-cyclopentenone to 1,3-cyclopentanedione with 5:1 enantiomeric discrimination. The racemate is kinetically resolved to (R)-4-hydroxy-2-cyclopentenone of 91% ee at 72% conversion at 0 °C (eq 4).7

Asymmetric Hydroboration.

Rhodium complexes are known to catalyze hydroboration of alkenes with unreactive borane derivatives, e.g. catecholborane and oxaborolidine.8 This reaction proceeds enantioselectively by use of BINAP as a ligand for neutral9-11 or cationic4,12 rhodium complexes. Reaction of styrene with catecholborane followed by oxidation affords (R)-1-phenylethanol in 96% ee in the presence of (R)-BINAP and [Rh(cod)2]BF4 (eq 5).4

Asymmetric Intramolecular Hydrosilation.

Intramolecular hydrosilation of allylic alcohols followed by oxidation is a convenient method for the stereoselective preparation of 1,3-diols.13 An enantioselective version is achieved by use of diene-free BINAP-Rh+ (eq 6).5 Both silyl ethers derived from cinnamyl alcohol and its cis isomer give (R)-1-phenylpropane-1,3-diol in high ee regardless of alkene geometry.

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; 2,2-Bis(diphenylphosphino)-1,1-binaphthyl; Chlorotris(triphenylphosphine)rhodium(I).

1. (a) Takaya, H.; Noyori, R. COS 1991, 8, Chapter 3.2. (b) Smith, K.; Pelter, A. COS 1991, 8, Chapter 3.10. (c) Hiyama, T.; Kusumoto, T. COS 1991, 8, Chapter 3.12. (d) Noyori, R.; Kitamura, M. In Modern Synthetic Methods, Sheffold, R., Ed.; Springer: Berlin, 1989; Vol. 5, p. 115. (e) Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Vol. 8.
2. (a) Miyashita, A.; Yasuda, A.; Takaya, H.; Toriumi, K.; Ito, T.; Souchi, T.; Noyori, R. JACS 1980, 102, 7932. (b) Miyashita, A.; Takaya, H.; Souchi, T.; Noyori, R. T 1984, 40, 1245.
3. Tani, K.; Yamagata, T.; Akutagawa., S.; Kumobayashi, H.; Taketomi, T.; Takaya, H.; Miyashita, A.; Noyori, R.; Otsuka, S. JACS 1984, 106, 5208.
4. (a) Hayashi, T.; Matsumoto, Y.; Ito, Y. JACS 1989, 111, 3426. (b) Hayashi, T.; Matsumoto, Y.; Ito, Y. TA 1991, 2, 601.
5. Bergens, S. H.; Noheda, P.; Whelan, J.; Bosnich, B. JACS 1992, 114, 2121.
6. Evans, D. A.; Morrissey, M. M.; Dow, R. L. TL 1985, 26, 6005.
7. Kitamura, M.; Manabe, K.; Noyori, R.; Takaya, H. TL 1987, 28, 4719.
8. Männig, D.; Nöth, H. AG(E) 1985, 24, 878.
9. Burgess, K.; Ohlmeyer, M. J. JOC 1988, 53, 5178.
10. Sato, M.; Miyaura, N.; Suzuki, A. TL 1990, 31, 231.
11. Zhang, J.; Lou, B.; Guo, G.; Dai, L. JOC 1991, 56, 1670.
12. Brown, J. M.; Lloyd-Jones, G. C. TA 1990, 1, 869.
13. (a) Tamao, K.; Nakajima, T.; Sumiya, R.; Arai, H.; Higuchi, N.; Ito, Y. JACS 1986, 108, 6090. (b) Tamao, K.; Tohma, T.; Inui, N.; Nakayama, O.; Ito, Y. TL 1990, 31, 7333.

Yoshihiko Ito & Michinori Suginome

Kyoto University, Japan

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