[19529-00-1]  · C72H62P4Ru  · Dihydridotetrakis(triphenylphosphine)ruthenium(II)  · (MW 1152.26)

(catalyst for hydration of nitriles,3 isomerization of alkynes,5,6 Knoevenagel reactions and conjugate additions,8 and transfer hydrogenation9)

Physical Data: light yellow dimagnetic solid, mp 180 °C.

Solubility: slightly sol benzene, toluene, THF.

Preparative Methods: prepared from Ruthenium(III) Chloride or ruthenium(III) acetylacetonate by reduction with Triethylaluminum in the presence of Triphenylphosphine in THF or benzene under nitrogen at room temperature.1 The complex can also be prepared by reaction of Dichlorotris(triphenylphosphine)ruthenium(II) with Sodium Borohydride and triphenylphosphine.2

Purification: recrystallization from benzene, toluene, or THF.

Handling, Storage, and Precautions: is air and light sensitive and should be stored under argon in the dark.

Amide Synthesis.

The hydration of nitriles with two equivalents of water in the presence of the title reagent (1) as catalyst gives the corresponding amide in good yields (eq 1).3 This reaction has been used in the transformation of d-ketonitriles to ene-lactams (eq 2). The ruthenium reagent also catalyzes reactions of amines with nitriles in aqueous medium at 160 °C to give amides in 75-95% yield (eq 3).4 This process has been extended to the preparation of polyamides.

Isomerization of Alkynes to Conjugated Dienes.

(E,E)-a,b,g,d-Dienones can be prepared stereoselectively from their corresponding a,b-unsaturated alkynyl ketones using the title reagent (1) as catalyst in a single step in good yields (eq 4).5 Other routes used to synthesize these compounds include the Horner-Wadsworth-Emmons reaction and the Knoevenagel condensation, which involve multiple steps and strong basic conditions and may provide isomeric mixtures of products. Aryl a,b-unsaturated alkynyl ketones rearrange more readily than alkyl a,b-unsaturated alkynyl ketones. Similarly, a,b-unsaturated alkynyl esters rearrange stereoselectively to the corresponding (2E,4E)-dienoic esters in the presence of (1) (eq 5).6 Inclusion of Tri-n-butylphosphine improves the yield of the reaction. This transformation has been extended to the preparation of o-alkoxy-(2E,4E)-dienoates, o-oxo-(2E,4E)-dienoates, and d-oxo-a,b,g,d-dienones.7

Aldol and Michael Reactions of Activated Nitriles.8

Nitriles react with aldehydes or ketones in the presence of (1) to give the corresponding a,b-unsaturated nitriles (eq 6). Michael addition of nitriles to a,b-unsaturated carbonyl compounds proceeds smoothly in the presence of (1) at rt under neutral conditions with high diastereoselectivity (eq 7). None of the corresponding aldol products is formed in the reaction.

Transfer Hydrogenation of Aldehydes and Ketones.9

The title reagent (1) has been used as a catalyst in the transfer of hydrogen from alcohols, such as isopropanol, cyclohexanol, and benzyl alcohol, and ethers, such as 2,5-dihydrofuran, to aldehydes and ketones in excellent yields (eq 8).

1. Yamamoto, A.; Kitazume, S.; Ikeda, S. JACS 1968, 90, 1089.
2. Young, R.; Wilkinson, G. Inorg. Synth. 1977, 17, 75.
3. Murahashi, S-I.; Sasao, S.; Saito, E.; Naota, T. JOC 1992, 57, 2521.
4. Murahashi, S.-I.; Naota, T.; Saito, E. JACS 1986, 108, 7846.
5. Ma, D.; Lin, Y.; Lu, X.; Yu, Y. TL 1988, 29, 1045.
6. Ma, D.; Lu, X. TL 1989, 30, 843.
7. Ma, D.; Lu, X. T 1990, 46, 6319.
8. Naota, T.; Taki, H.; Mizuno, M.; Murahashi, S.-I. JACS 1989, 111, 5954.
9. Imai, H.; Nishiguchi, T.; Fukuzumi, K. JOC 1976, 41, 665.

Shomir Ghosh

Parke-Davis Pharmaceutical Research, Ann Arbor, MI, USA

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