Mechanism in homogeneous catalysis; NMR as a prime mover

Brown, John M.

doi:10.1016/j.jorganchem.2004.07.018

Cited by 14 publications

(3 citation statements)

References 81 publications

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“…In general, conventional Ir diphosphine complexes turnover slowly or not at all when enantioselective hydrogenation of standard substrates is attempted, and essentially all the practical and useful recent synthetic contri- butions stem from the use of phosphinamine, phosphinocarbene or aminocarbene chelates. The state of current knowledge on intermediates in rhodium-complex-catalyzed enantioselective hydrogenation is summarized in Figure 31.14, specifying the route for production of the favored enantiomer [62]. Consider the sequence of NMR-characterized species shown in Figure 31.13.…”

Section: Current Status Of Rhodium Hydrogenationsmentioning

confidence: 99%

Mechanism of Enantioselective Hydrogenation

Brown¹

2006

The Handbook of Homogeneous Hydrogenation

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John M. Brown IntroductionThe discovery of the first practical catalyst for homogeneous hydrogenation by Wilkinson, Osborn, Jardine and Young in 1965 [1] occurred at around the same time that others, especially Mislow and Horner [2], were demonstrating that chiral trivalent phosphorus compounds were capable of existing as stable, noninterconverting enantiomers. With suitable adaptation of Wilkinson's catalyst, a prostereogenic alkene could be hydrogenated with preferential formation of one enantiomer of the reduced product. The possibility of such enantioselective hydrogenation was recognized by both Horner [3] and Knowles [4], but it was Knowles who won the race to demonstrate the first example in 1968. This led rapidly to a period of seminal discoveries: the application of chelate biphosphine ligands came from Kagan [5], and the development of a full-scale enantioselective hydrogenation of a dehydroamino acid to provide a rhodium-complex-based catalytic synthesis of l-Dopa by Knowles' team at Monsanto [6]. For many years this provided a substantial part of the supply of the main drug active in the control of Parkinson's disease. Kagan was also the first to demonstrate, in his synthesis and application of DIOP (derived very simply from RR-or SS-tartaric acid), that the difficult synthesis of enantiomerically pure phosphines was unnecessary for effective enantioselective hydrogenation, since a suitable chelate backbone could provide the necessary level of stereochemical control. For many years the development of enantioselective hydrogenation converged on the preparation of enantiomerically pure chelate diphosphines and the application of their rhodium complexes to the hydrogenation of dehydroamino acids, enamides and closely related reactants [7]. Although both ruthenium [8] and iridium catalysts [9] for homogeneous hydrogenation were known at an early stage, the development of effective enantioselective hydrogenation in these two spheres occurred much later. For ruthenium enantioselective hydrogenation, the spectacular efficiency of BINAP catalysts [10] developed by Noyori's group was first demonstrated for alkenes, and then in rather greater depth for ketones [11]. The high efficiency of iridium complexes in hydrogenation had been demonstrated 1073The Handbook of Homogeneous Hydrogenation. Edited by J. G. de Vries and C. J. Elsevier

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Section: Current Status Of Rhodium Hydrogenationsmentioning

confidence: 99%

Mechanism of Enantioselective Hydrogenation

Brown¹

2006

The Handbook of Homogeneous Hydrogenation

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“…[ 7–9 ] To date, a large number of chiral catalysts with very high catalytic activity for enantioselective catalysis has been published in the literature. [ 10–15 ] However, the industrial applications of these privileged stereodirecting chiral catalysts are often hindered by their high costs, the inability to recover them after their use, and the removal of these toxic metals from the organic product. Many different approaches have been tried to facilitate easy recovery and recycling of highly selective chiral catalysts.…”

Section: Introductionmentioning

confidence: 99%

Readily accessible mesoporous silica nanoparticles supported chiral urea‐amine bifunctional catalysts for enantioselective reactions

Gök

Aykut

Gök

2020

Applied Organom Chemis

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The main objective of this study is to develop readily accessible and recyclable solid catalysts for enantioselective reactions. To achieve this, magnetic MCM‐41 and non‐magnetic SBA‐15 mesoporous supports were prepared, then mesoporous silica supported chiral urea‐amine bifunctional catalysts were synthesized by grafting of chiral urea‐amine ligand onto SBA‐15 and magnetic MCM‐41. The magnetic and non‐magnetic supports and so‐prepared solid catalysts were characterized by using different methods such as N2 sorption measurements, Fourier transform infrared spectroscopy (FT‐IR), field emission scanning electron microscope‐energy dispersive X‐ray analysis (FESEM‐EDX), X‐ray diffraction (XRD), and thermogravimetric analysis (TGA). Results showed that (1R, 2R) or (1S, 2S)‐1,2‐diphenylethane‐1,2‐diamine was successively immobilized onto magnetic MCM‐41 and SBA‐15 pores. The heterogeneous chiral solid catalysts and their homogenous counterparts exhibited high activities both enantioselective transfer hydrogenation reaction (up to 99% conversion and 65% ee) and enantioselective Michael reaction (up to 98% conversion and 26% ee). Moreover, the SBA‐15 supported solid catalysts were separated from the reaction mixture by simple filtration, whereas the magnetic MCM‐41 supported solid catalysts were separated by simple magnetic decantation and reused in three consecutive catalytic experiments.

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“…Spectroscopy-based detection techniques are often employed for catalyst screening. However, these methods rely on the presence of chromophores and fluorophores in either substrate or product for detection of catalytic activity. − Consequently, in order to expand the application range, alternative detection methodologies are being developed for catalyst screening. − In this perspective, mass spectrometry (MS) offers exceptional specificity and selectivity for the sensitive detection of (multiple) selected target molecules in complex matrixes . The applicability of mass spectrometric detection and its impact on high-throughput screening was reviewed by Niessen, who concluded that the widespread use and increasing number of publications in the field of high-throughput screening is an indicator for the progress that has been made in terms of both applications and instrumentation .…”

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Online Screening of Homogeneous Catalyst Performance using Reaction Detection Mass Spectrometry

et al. 2008

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An integrated online screening system was developed to rapidly screen homogeneous catalysts for activity toward a selected synthesis. The continuous-flow system comprises standard HPLC pumps for the delivery of substrates, an HPLC autosampler for the injection of homogeneous catalysts, a thermostated reactor to mediate synthesis, and a single-stage quadrupole mass spectrometer (MS) equipped with atmospheric pressure chemical ionization for the determination of product formation. MS detection offers sensitivity, specificity, and speed when applied to the analysis of dynamic processes in the condensed phase. By applying the present methodology for the study of substrate conversion mediated by homogeneous catalysts, the concentration of substrates and reaction product could be monitored while information about the catalysts could also be obtained. In an initial screening application, the performance of a selected number of Lewis acids in the multicomponent synthesis of a highly substituted 2-imidazoline was determined. Limit of detection and limit of quantitation were determined by injecting different concentrations of 2-imidazoline standards and proved to be 1.6 and 5.2 nM, respectively. The results obtained with the new screening method were in good agreement with a traditional bench-scale experiment. Moreover, the system was capable of determining catalyst performance with very low catalyst and solvent consumption while the ruggedness of the system was exhibited with a 24-h continuous analysis of 280 successive catalyst injections with a peak area variation within 7% relative standard deviation.

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Mechanism in homogeneous catalysis; NMR as a prime mover

Cited by 14 publications

References 81 publications

Mechanism of Enantioselective Hydrogenation

Mechanism of Enantioselective Hydrogenation

Readily accessible mesoporous silica nanoparticles supported chiral urea‐amine bifunctional catalysts for enantioselective reactions

Online Screening of Homogeneous Catalyst Performance using Reaction Detection Mass Spectrometry

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