Catalytic Transfer Hydrogenation of Ketones with KHCr(CO)5/HCO2H/Et3N Systems

Brunet, Jean‐Jacques; Chauvin, Rémi; Leglaye, Pascale

doi:10.1002/(sici)1099-0682(199904)1999:4<713::aid-ejic713>3.0.co;2-h

Cited by 11 publications

(15 citation statements)

References 22 publications

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“…These hypotheses have been used to design a system for the catalytic reduction of ketones in the presence of a hydrogen-transfer agent [KHCr(CO) 5 /HCO 2 H/Et 3 N] (vide infra, Part 5). [49] …”

Section: Reaction With Aldehydes and Ketonesmentioning

confidence: 98%

“…[48] These conclusions are relevant to the recent observation that, in contrast to the [PPN] ϩ salt, the potassium salt [K] ϩ [HCr(CO) 5 ] Ϫ does react with cyclohexanone in the absence of acid. [49] The stoichiometric reaction of [K] ϩ [HCr(CO) 5 ] Ϫ with cyclohexanone at room temperature in THF leads, after hydrolysis, to cyclohexanol (50% yield, 24 h) [Equation (26)]. (26) However, the yield could not be increased by using longer reaction times (120 h).…”

Section: Reaction With Aldehydes and Ketonesmentioning

confidence: 99%

“…In this reaction, KHCr(CO) 5 proved to be much more reactive than KHFe(CO) 4 or KHCr 2 (CO) 10 . [49] ( 31) Methyl acrylate was also found to be rapidly reduced, yielding methyl propionate within 10 min (90% yield). However, in several cases the α,β-unsaturated ketones and esters were only partially reduced to the saturated ketones and high molecular weight products were generated.…”

Section: Reactivity Towards C‫؍‬c Double Bondsmentioning

confidence: 99%

“…(49)]. [80] ( 49) In these reactions, terminal hydrides [HM(CO) 5 ] Ϫ are also involved as key intermediates in the generation of formato complexes [HCO 2 M(CO) 5 ] Ϫ . In Scheme 7, the proposed catalytic cycle is represented in the case of the tungsten complex.…”

Section: Catalytic Synthesis Of Alkyl Formates From Carbon Dioxidementioning

confidence: 99%

“…[51] The stoichiometric reaction of [Et 4 N] ϩ -[HCr(CO) 5 ] Ϫ with acetophenone (no solvent) was monitored by GC and IR analysis. The results were interpreted in terms of Equation (55), where both H atoms involved in the reduction originate from [HCr(CO) 5 ] Ϫ , a proposal that has been criticized, [81] but also seems to be valid for the [49] ( 55) On the basis of these results, it has been proposed that the intermediate is an alkoxocarbonylchromate. [51] Evidence supporting this hypothesis is provided by the stereochemical outcome of the hydrogenation of 4-tert-butylcyclohexanone (Table 4).…”

Section: Catalytic Hydrogenations Of Aldehydes and Ketonesmentioning

confidence: 99%

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Pentacarbonylhydridochromates M+[HCr(CO)5]−: Reactivity in Organic Synthesis and Homogeneous Catalysis

Brunet

2000

Eur. J. Inorg. Chem.

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Section: Reaction With Aldehydes and Ketonesmentioning

confidence: 98%

Section: Reaction With Aldehydes and Ketonesmentioning

confidence: 99%

Section: Reactivity Towards C‫؍‬c Double Bondsmentioning

confidence: 99%

Section: Catalytic Synthesis Of Alkyl Formates From Carbon Dioxidementioning

confidence: 99%

Section: Catalytic Hydrogenations Of Aldehydes and Ketonesmentioning

confidence: 99%

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Pentacarbonylhydridochromates M+[HCr(CO)5]−: Reactivity in Organic Synthesis and Homogeneous Catalysis

Brunet

2000

Eur. J. Inorg. Chem.

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Ionic Hydrogenations

Bullock¹

2006

The Handbook of Homogeneous Hydrogenation

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7 Ionic Hydrogenations 7 Ionic Hydrogenations 154 Scheme 7.1sis documents the early progress in this field; a book gives further details [2]. As shown in Eq. (2), proton transfer to the alkene generates a carbenium ion, and hydride transfer from the hydrosilane generates the product. 2Ionic hydrogenations of C=C bonds generally work well only in cases where a tertiary or aryl-substituted carbenium ion can be formed through protonation of the C=C bond. Alkenes that give a tertiary carbenium ion upon protonation include 1,1-disubstituted, tri-substituted and tetra-substituted alkenes, and each of these are usually hydrogenated by ionic hydrogenation methods in high yields.The success of stoichiometric ionic hydrogenations is due to achieving a fine balance that favors the intended reactivity rather than any of several possible alternative reactions. The acid must be strong enough to protonate the unsaturated substrate, yet the reaction of the acid and the hydride should avoid producing H 2 too quickly under the reaction conditions. The commonly used pair of CF 3 CO 2 H and HSiEt 3 meets all these criteria.The very strong acid, CF 3 SO 3 H (triflic acid, abbreviated as HOTf) can be used in conjunction with HSiEt 3 for the hydrogenation of certain alkenes [3]. These reactions proceed cleanly in 5 minutes at -50 8C. This discovery was surprising, since a review of the use of CF 3 CO 2 H and HSiEt 3 had stated that "F F F stronger acids cannot be used in conjunction with silanes because they react" [1]. Indeed, rapid evolution of H 2 does occur when HOTf is added to HSiEt 3 in the absence of an alkene. The order of addition is important in the use of HOTf/HSiEt 3 for hydrogenation of C=C bonds, to ensure that acid-induced formation of H 2 is minimized. The addition of HOTf to a solution containing the alkene and the hydrosilane results in rapid and clean hydrogenation, but the reaction is still subject to the limitation of forming a tertiary carbenium ion.Another potential mechanistic complication is capture of the intermediate carbenium ion by the conjugate base of the acid. When CF 3 CO 2 H is used as the acid, this would lead to trifluoroacetate esters. Kursanov et al. showed that, under the reaction conditions for ionic hydrogenations, trifluoroacetate esters can be converted to the hydrocarbon product (Eq. (3)). 7.2 Stoichiometric Ionic Hydrogenations 155 7 Ionic Hydrogenations 7.2 Stoichiometric Ionic Hydrogenations 161 Scheme 7.3 Thermodynamic cycle for determination of the hydricity using heterolytic cleavage of hydrogen. 38 7.3.6 Catalytic Hydrogenation of Iminium Cations by Ru ComplexesNorton and coworkers found that catalytic enantioselective hydrogenation of the C=N bond of iminium cations can be accomplished using a series of Ru complexes with chiral diphosphine ligands such as Chiraphos and Norphos [68]. Even tetra-alkyl-substituted iminium cations can be hydrogenated by this method. These reactions were carried out with 2 mol.% Ru catalyst and 3.4-3.8 bar H 2 at room temperature in CH 2 Cl 2 solvent (Eq....

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Transferhydrogenations

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Alberico²

2004

Transition Metals for Organic Synthesis

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Catalytic Transfer Hydrogenation of Ketones with KHCr(CO)5/HCO2H/Et3N Systems

Cited by 11 publications

References 22 publications

Pentacarbonylhydridochromates M+[HCr(CO)5]−: Reactivity in Organic Synthesis and Homogeneous Catalysis

Pentacarbonylhydridochromates M+[HCr(CO)5]−: Reactivity in Organic Synthesis and Homogeneous Catalysis

Ionic Hydrogenations

Transferhydrogenations

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