Bis(bicyclo[2.2.1]hepta-2,5-diene)rhodium Perchlorate1

[60576-58-1]  · C14H16ClO4Rh  · Bis(bicyclo[2.2.1]hepta-2,5-diene)rhodium Perchlorate  · (MW 386.64)

(precursor for various cationic rhodium complexes,2 which are used as catalysts for hydrogenation,3 allylic hydrogen migration,4 hydrosilation,5 and hydroacylation6)

Alternate Name: [Rh(nbd)2]ClO4.

Solubility: sol CH2Cl2; insol THF, hexane.

Form Supplied in: rust-brown crystals containing 1 mol THF solvent of crystallization.

Preparative Methods: to a mixture of bicyclo[2.2.1]hepta-2,5-diene (nbd, 0.14 g, 1.5 mmol) and Bis(bicyclo[2.2.1]hepta-2,5-diene)dichlorodirhodium (0.35 g, 0.75 mmol) in CH2Cl2 (15 mL) at room temperature is added Silver(I) Perchlorate (0.315 g, 1.5 mmol) under nitrogen. After stirring for 1 h, precipitated AgCl is filtered off to give a CH2Cl2 solution of [Rh(nbd)2]ClO4. This solution can be directly used for the next reaction,7 or diluted by THF (15 mL) followed by evaporation of CH2Cl2 under vacuum to separate orange needles of [Rh(nbd)2]ClO4, which are collected and washed with cold THF and then dried in vacuo to afford rust-brown crystals (0.5 g).8 For another preparation from [RhCl(C2H4)2], see Fairlie and Bosnich.6

Handling, Storage, and Precautions: explosive when heated.

Preparation of Cationic Rhodium Complexes.

Cationic rhodium complexes are useful homogeneous catalysts in organic synthesis. In particular, many selective reactions have been accomplished by use of cationic rhodium complexes with various ligands, i.e. phosphines, pyridine derivatives, and bidentate phosphines. These complexes are expeditiously prepared from [Rh(diene)2]+X- by ligand exchange, where only one diene is replaced by two monodentate ligands or a single bidentate ligand (eq 1).9 The complexes thus obtained are used as catalysts, or further treated with molecular hydrogen to afford diene-free complexes, which can also be employed as catalysts (eq 2).2

Hydrogenation Catalysts.

The cationic rhodium complexes effectively catalyze hydrogenation of carbon-carbon9 as well as carbon-oxygen10 multiple bonds. Bidentate phosphine ligands are most frequently used, and certain chiral ligands induce high enantioselectivities.

Asymmetric hydrogenation of dehydroamino acids to optically active a-amino acids has been studied most extensively. The high optical yields (>90% ee) are attained with BINAP,3 CHIRAPHOS,8 CAPP,11 SKEWPHOS,12 etc. as ligands in hydrogenation of a-(acylamino)cinnamic acid derivatives (eq 3). Itaconic acid is also hydrogenated in the presence of a (S,S)-CAPP-Rh complex to afford (R)-methylsuccinic acid in 95% ee.11

Hydrogenation of ketones is effectively catalyzed by cationic rhodium complexes with phosphine ligands having alkyl substituents on the phosphorus atom, while arylphosphine-rhodium complexes show only a low catalytic activity.10,13 Another kind of remarkable catalyst is the cationic rhodium complex with (R)-(S)-BPPFOH, which catalyzes hydrogenation of 3,4-dihydroxyphenyl (N-methylamino)methyl ketone hydrochloride in 95% ee to afford the corresponding 2-amino alcohol, e.g. epinephrine (eq 4).14

Isomerization of Allylamines to Enamines.

Allylic hydrogen migration is catalyzed by cationic rhodium complexes. With optically active bidentate phosphines, i.e. BINAP, achiral allylamines isomerize to optically active enamines in high enantiomeric excess (eq 5).4

Hydrosilation.

Asymmetric hydrosilation of prochiral ketones is promoted by cationic rhodium complexes with AMPHOS15 as well as DIOP16 to afford the corresponding alcohols in modest to good enantioselectivities. Carbon-carbon double bonds in allylic alcohols are intramolecularly hydrosilated in a highly enantioselective manner. Subsequent H2O2 oxidation affords optically active 1,3-diols (eq 6).5

Hydroacylation.

Cationic rhodium complexes which have bidentate phosphine ligands mediate the hydroacylation of substituted 4-pentenals to cyclopentanones (eq 7).6 Cationic catalysts are superior in activity to neutral ones such as Wilkinson's catalyst.17

For a more detailed discussion of catalytic asymmetric syntheses via rhodium complexes, see those entries that deal specifically with rhodium complexes/optically active ligand combinations.

Related Reagents.

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; 2,2-Bis(diphenylphosphino)-1,1-binaphthyl; (E)-(3-Chloro-1-methyl-1-propenyl)trimethylsilane; (1,5-Cyclooctadiene)[(3R,4R)-3,4-bis(diphenylphosphino)-1-methylpyrrolidine]rhodium Tetrafluoroborate; Chlorotris(triphenylphosphine)rhodium(I).


1. (a) Harada, K.; Munegumi, T. COS 1991, 8, Chapter 1.6. (b) Takaya, H.; Noyori, R. COS 1991, 8, Chapter 3.2. (c) Smith, K.; Pelter, A. COS 1991, 8, Chapter 3.10. (d) Hiyama, T.; Kusumoto, T. COS 1991, 8, Chapter 3.12. (e) Comprehensive Organometallic Chemistry; Wilkinson, G., ed.; Pergamon: Oxford 1982; Vol. 8.
2. (a) Schrock, R. R.; Osborn, J. A. JACS 1971, 93, 2397. (b) Green, M.; Kuc, T. A. JCS(D) 1972, 832.
3. Miyashita, A.; Takaya, H.; Souchi, T.; Noyori, R. T 1984, 40, 1245.
4. Tani, K.; Yamagata, T.; Akutagawa, S.; Kumobayashi, H.; Taketomi, T.; Takaya, H.; Miyashita, A.; Noyori, R.; Otsuka, S. JACS 1984, 106, 5208.
5. Bergens, S. H.; Noheda, P.; Whelan, J.; Bosnich, B. JACS 1992, 114, 2121.
6. Fairlie, D. P.; Bosnich, B. OM 1988, 7, 936.
7. Usón, R.; Oro, L. A.; Cuchi, J. A.; Garralda, M. A. JOM 1976, 116, C35.
8. Fryzuk, M. D.; Bosnich, B. JACS 1977, 99, 6262.
9. Shapley, J. R.; Schrock, R. R.; Osborn, J. A. JACS 1969, 91, 2816.
10. Schrock, R. R.; Osborn, J. A. CC 1970, 567.
11. N-(N-Substituted carbamoyl)-4-diphenylphosphino-2-diphenylphosphinomethylpyrrolidines: Ojima, I.; Yoda, N. TL 1980, 21, 1051.
12. (S,S)- or (R,R)-2,4-bis(diphenylphosphino)pentane: MacNeil, P. A.; Roberts, N. K.; Bosnich, B. JACS 1981, 103, 2273.
13. Tani, K.; Suwa, K.; Tanigawa, E.; Yoshida, T.; Okano, T.; Otsuka, S. CL 1982, 261.
14. (R)-1-(S)-1,2-Bis(diphenylphosphino)ferrocenylethanol: Hayashi, T.; Katsumura, A.; Konishi, M.; Kumada, M. TL 1979, 425.
15. N,N-Dimethyl-1-{o-(diphenylphosphino)phenyl}ethylamine: Payne, N. C.; Stephan, D. W. IC 1982, 21, 182.
16. 2,3-O-Isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane: Hayashi, T.; Yamamoto, K.; Kasuga, K.; Omizu, H.; Kumada, M. JOM 1976, 113, 127.
17. Larock, R. C.; Oertle, K.; Potter, G. F. JACS 1980, 102, 190.

Yoshihiko Ito & Michinori Suginome

Kyoto University, Japan



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