[1828-36-1]  · C72H61P4Rh  · Hydridotetrakis(triphenylphosphine)rhodium  · (MW 1153.12)

(catalyst for hydrogenation of alkenes2 and hydrosilylation of alkynes3)

Physical Data: mp 162-163 °C.

Solubility: slightly sol benzene, toluene, THF, acetone.

Form Supplied in: yellow crystals.

Preparative Methods: from Rhodium(III) Chloride or rhodium(III) acetylacetonate by reduction with Triethylaluminum in the presence of Triphenylphosphine.1a,b

Purification: by recrystallization from toluene or benzene.

Handling, Storage, and Precautions: solid material is moderately sensitive to oxygen, but in solution it is easily decomposed by air.

Hydrogenation of Activated Alkenes by using a Hydrogen Donor.2

A number of different substituted styryl ketones have been reduced by 1-phenylethanol at 50 °C in the presence of catalytic amounts of (PPh3)4RhH (eq 1). The initial rate of reduction increases when the aromatic ring contains electron-withdrawing groups and decreases in the presence of electron-releasing substituents.

Hydrosilylation of Alkynes.3

Hydrosilylation of acetylene with trichlorosilane, triethoxysilane, methyldichlorosilane, methyldiethoxysilane, and n-hexyldichlorosilane takes place in either xylene or toluene in the presence of catalytic amounts of (PPh3)4RhH (eq 2).

Synthesis of a-Trimethylsilyl Ketones.4

a-Trimethylsilyl ketones are useful compounds in the synthesis of di- and trisubstituted alkenes5 and in aldol reactions.6 The preparation of such ketones can be carried out by any of the following reactions catalyzed by (PPh3)4RhH: isomerization of b-trimethylsilyl allyl alcohols, isomerization of b-trimethylsilyl allyl alcohols, or dehydrogenation of b-trimethylsilyl alcohols via hydrogen transfer to a,b-enones.

Isomerization of 1,3-Diene Monoepoxides to a,b-Unsaturated Carbonyl Compounds.7

(E)-a,b-Unsaturated carbonyl compounds can be selectively obtained from the Rh-catalyzed isomerization of vinyl epoxides (eq 3). The starting monoepoxides can be prepared according to eq 4.7

Other applications include removal of the allyl ether protecting group in the presence of trifluoroacetic acid,8 and the synthesis of allylsilanes.9

1. (a) Yamamoto, A.; Kitazume, S.; Ikeda, S. JACS 1968, 90, 1089. (b) Ito, T.; Kitazume, S.; Yamamoto, A.; Ikeda, S. JACS 1970, 92, 3011.
2. Beaupere, D.; Bauer, P.; Uzan, R. CJC 1979, 57, 218.
3. Watanabe, H.; Asami, M.; Nagai, Y. JOM 1980, 195, 363.
4. Sato, S.; Matsuda, I.; Izumi, Y. JOM 1988, 344, 71.
5. Hudrlik, P. F.; Peterson, D. JACS 1975, 97, 1464.
6. Inoue, T.; Sato, T.; Kuwajima, I. JOC 1984, 49, 4671.
7. Sato, S.; Matsuda, I.; Izumi, Y. JOM 1989, 359, 255.
8. Ziegler, F. E.; Brown, E. G.; Sobolov, S. B. JOC 1990, 55, 3691.
9. Matsuda, I.; Kato, T.; Sato, S.; Izumi, Y. TL 1986, 27, 5747.

Eduardo Peña-Cabrera

Emory University, Atlanta, GA, USA

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