Hydride Transfer by Hydrido Transition‐Metal Complexes. Ionic Hydrogenation of Aldehydes and Ketones, and Structural Characterization of an Alcohol Complex

Song, Jeong-Sup; Szalda, David J.; Bullock, R. Morris; Lawrie, Christophe J. C.; Rodkin, Mikhail A.; Norton, Jack R.

doi:10.1002/anie.199212331

Cited by 76 publications

(56 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[22] When the acidity was held constant by a buffer, the reaction was shown to be second-order overall, first order in aldehyde, and first order in metal hydride. The proposed mechanism that is consistent with all the observations is a pre-equilibrium proton transfer to the substrate, followed by rate-determining hydride transfer, as shown in Scheme 5.…”

Section: Stoichometric Ionic Hydrogenations With An External Acid As mentioning

confidence: 99%

“…Our expectation was correct in predicting the thermodynamic product, but an unexpected kinetic product was discovered (Scheme 4). [22] The reaction of acetone with [W(Cp)(CO) 3 and HOTf gave a complex with an isopropyl alcohol ligand. The alcohol ligand was generated in the hydrogenation reaction without leaving the metal.…”

Section: Stoichometric Ionic Hydrogenations With An External Acid As mentioning

confidence: 99%

See 1 more Smart Citation

Catalytic Ionic Hydrogenations

Bullock

2004

Chemistry A European J

Self Cite

287

206

View full text Add to dashboard Cite

Catalytic ionic hydrogenation of ketones occurs by proton transfer to a ketone from a cationic metal dihydride, followed by hydride transfer from a neutral metal hydride. This contrasts with traditional catalysts for ketone hydrogenation that require binding of the ketone to the metal and subsequent insertion of the ketone into a M-H bond. Ionic hydrogenation catalysts based on the inexpensive metals molybdenum and tungsten have been developed based on mechanistic understanding of the individual steps required in the catalytic reaction.

show abstract

Section: Stoichometric Ionic Hydrogenations With An External Acid As mentioning

confidence: 99%

Section: Stoichometric Ionic Hydrogenations With An External Acid As mentioning

confidence: 99%

Catalytic Ionic Hydrogenations

Bullock

2004

Chemistry A European J

Self Cite

287

206

View full text Add to dashboard Cite

show abstract

“…Extensive studies on stoichiometric hydrogenations of ketones have been carried out using HOTf as an acid, and metal carbonyl hydrides such as [Cp(CO) 3 WH] as the hydride donor [41,42]. The addition of HOTf to a solution containing acetone and the tungsten hydride [Cp(CO) 3 WH] at 22 8C results in hydrogenation of the C=O bond to the alcohol, with the kinetically stabilized product having an alcohol ligand bound to the metal (Scheme 7.7) [41,42].…”

mentioning

confidence: 99%

Ionic Hydrogenations

Bullock¹

2006

The Handbook of Homogeneous Hydrogenation

Self Cite

View full text Add to dashboard Cite

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....

show abstract

“…The C = O bond of ketones can also be hydrogenated through reactions with HOTf and metal hydrides [42] . Reaction of acetone with HOTf and Cp(CO) 3 WH gives stoichiometric hydrogenation of the C = O bond, initially giving a product with the alcohol bound to the metal as a kinetically stabilized complex (3.13) .…”

Section: Ionic Hydrogenation Of Ketones Using Metal Hydrides and Addementioning

confidence: 99%

Hydride Transfer by Hydrido Transition‐Metal Complexes. Ionic Hydrogenation of Aldehydes and Ketones, and Structural Characterization of an Alcohol Complex

Cited by 76 publications

References 20 publications

Catalytic Ionic Hydrogenations

Catalytic Ionic Hydrogenations

Ionic Hydrogenations

Molybdenum and Tungsten Catalysts for Hydrogenation, Hydrosilylation and Hydrolysis

Contact Info

Product

Resources

About