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comprehensive catalytic hydrogenation overview
(Rated as: excellent)
The Reductive Amination of Aldehydes and Ketones and the Hydrogenation of Nitriles: Mechanistic Aspects and Selectivity Control
(S. Gomez, J.A. Peters, T. Maschmeyer; Advanced Synthesis And Catalysis Vol. 344 Issue 10 (1037-1057))
This review deals with two of the most commonly used methods for the preparation of amines: the reductive amination of aldehydes and ketones and the hydrogenation of nitriles. There is a great similarity between these two methods, since both have the imine as intermediate. However, due to the high reactivity of this intermediate, primary, secondary and/or tertiary amines are obtained (often simultaneously). The relation of the selectivity to different substrate structures and reaction conditions is briefly summarized, the main focus being on the catalyst as it is the most significant factor that governs the selectivity. Different mechanisms are discussed with the view to correlate the structure the catalyst and, more particularly, the nature of the metal and the support with selectivity. The crucial point is the presumed location of the condensation and hydrogenation steps.
Table of Contents:
2 Reaction Mechanisms and By-Products
2.1 Reductive Amination of Aldehydes and Ketones
2.2 Hydrogenation of Nitriles
3 Effect of the Substrate Structure
3.1 Steric effects
3.2 Electronic Effects
4 Effect of the Reaction Conditions
4.1 Effect of Binding Primary Amines with Acids, Ammonium Salts and Acetic Anhydride
4.2 Effect of the Addition of NH3
4.3 Effect of the Addition of H2O
4.4 Effect of the Addition of Hydroxides and Carbonates
5 Effect of the Catalyst
5.1 Location of the reaction steps
5.2 Effect of the Support
5.3 Effect of the Metal
keywords: aldehydes; amination; heterogeneous catalysis; hydrogenation; ketones; nitriles
(feel free to move this thread to the Chemistry or Novel Discourse forums; I wasn't sure where to post it as I am quite new here)
enantioselective CTH reductive amination
(Rated as: good read)
Highly Enantioselective Hydrogen-transfer Reductive Amination: Catalytic Asymmetric Synthesis of Primary Amines
(Renat Kadyrov, Thomas A. Riermeier; AngewandteChemie 115, 44 (5630-5632))
Development of a highly stereoselective Ruthenium complex catalyst ([((R)-TOL-BINAP)RuCl2]) for Leuckart-Wallach like transfer hydrogenation of acetophenone and other aromatic ketones, using ammonium formate as hydrogen/ammonia donor.
I am aware that such exotic catalysts aren't really very available - but this one is interesting anyway (>90% enantioselectivity, with amine yield - after hydrolysis of the formyl derivative - being also around 90%), isn't it?
reductive amination using rhodium catalyst
(Rated as: good read)
On the Reductive Amination of aldehydes and ketones catalysed by homogenous Rh(I) catalysts
(V.I. Tararov, R. Kadyrov, T.H. Riermeier, A Boerner; Chem.Commun. 2000 (p1867-1868))
The homogeneously catalyzed reductive amination of aldehydes and ketones under smooth conditions is reported, showing for the first time, that Rh(I) catalysts based on chelating diphosphines and diphosphinites can be advantageously employed for this reaction, even for the production of chiral amino acid derivatives.
One-stage (or direct) reductive amination of aldehydes and ketones with amines affording higher alkylated amines is an interesting target in modern organic chemistry with great synthetic potential for application in academia and industry. Hitherto several chemical reducing agents, in particular borohydrides, have been shown to be valuable for this reaction giving rise to the alkylated amines in good yield. 1 However, from the ecological point of view and taking into account the demand for atom economy, more promising is the use of molecular hydrogen as a reducing agent. Indeed it was shown that reductive amination with hydrogen can be mediated by heterogeneous platinum, palladium, nickel or ruthenium metal catalysts. 2 Several amines have been prepared by this methodology even on an industrial scale.(...)
|C=C hydrogenation using Pd on carbon nanotubes
Carbon nanofiber supported palladium catalyst for liquid-phase reactions. An active and selective catalyst for hydrogenation of CC bonds
(C. Pham-Huu, N. Keller, L. J. Charbonniere, R. Ziessel, M. J. Ledoux; Chem. Commun. 2000, 19 (1871 - 1872))
Carbon nanofibers with a mean diameter of about 50 nm were successfully used as support for a palladium catalyst in the liquid phase selective hydrogenation of the C=C bond in an alpha,beta-unsaturated molecule: a less critical problem of mass-transfer limitation led to the obtention of a highly active and chemo-selective catalyst compared to a commercial high surface area activated charcoal supported palladium catalyst.
Since their discovery at the beginning of the last decade, 1 carbon nanotubes and nanofibers seemed to be promising candidates for use as catalyst supports for heterogeneous catalytic reactions. Such materials were expected to be efficient in liquid phase media due to their high external surfaces which can allow a significant decrease in critical mass transfer limitations, also leading to an increase in the rate and the selectivity of the reactions.
The aim of the present communication is to report the preparation of a highly dispersed palladium catalyst supported on carbon nanofibers, which is active and chemo-selective in the liquid phase hydrogenation of the CC bond of cinnamaldehyde, at atmospheric pressure. The reaction rate and the product distribution are compared with those obtained on a commercially available activated charcoal supported palladium catalyst under the same reaction conditions.
Again, nanofiber-supported palladium isn't very available; but they selectively hydrogenate the double bond in cinnamaldehyde with it, for example...
|red. amination with Rh(1)-diphosphane catalyst
A Scrutiny on the Reductive Amination of Carbonyl Compounds Catalyzed by Homogeneous Rh(I) Diphosphane Complexes
Vitali I. Tararov, Renat Kadyrov, Thomas H. Riermeier, Armin Börner
Advanced Synthesis and Catalysis 2002 (344), 2 (200-208)
amination • homogeneous catalysis • phosphane • reduction • rhodium
The reductive amination of a series of aldehydes with secondary amines and H2 in the presence of a homogeneous Rh-diphosphane catalyst was studied in order to establish a general mechanism of this reaction and to identify conditions for the improvement of the amine/alcohol ratio in the product. Several possible intermediates as constituents of changing equilibria like half-aminals, N,O-acetals and aminals were observed in the reaction mixture by means of 1H NMR spectroscopy. In individual trials, these compounds could be successfully hydrogenated under the conditions applied for reductive amination (50 bar H2 pressure, MeOH). Some evidence is accumulated that half-aminals and N,O-acetals might be key intermediates of the reductive amination. Moreover, it was found that the formation of the undesired product alcohol is likely based on the reduction of the starting carbonyl compound. However, due to numerous equilibria consisting of several intermediates, general conclusions are hard to be drawn. Proof will be given that, in several cases, the efficiency of the reductive amination of aliphatic aldehydes can be significantly improved by prehydrogenation of the cationic [Rh(dppb)(COD)]+ complex.
*** Now with Lego-conform layout! ***
(I hope it is correct this way?)