1
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Chen R, Xu B, Cheng H, Fang Q, Ma M, Qian L, Wan S, Xu S, Li Y, Zhang L, Xiang S. Enhanced interfacial effect via acid theory with boosted photocatalytic performance of nitenpyram removal. CHEMOSPHERE 2024; 356:141948. [PMID: 38604521 DOI: 10.1016/j.chemosphere.2024.141948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/01/2024] [Revised: 03/25/2024] [Accepted: 04/06/2024] [Indexed: 04/13/2024]
Abstract
Surface reaction is a prominent aspect that affects the efficiency of photocatalysis. In this work, acid theory was employed to facilitate the reaction dynamics and enhance the interfacial effect between photocatalysts and target molecules. The photocatalytic removal efficiency of NTP was 66 % for bare CdS in 50 min with apparent rate constants of 0.023 compare to 96 % with apparent rate constants of 0.065 for 5% Ce-CdS. The introduced Ce atom as bifunctional active site reduces the energy barrier of O2 adsorption, strengthens the interfacial effect and accelerates the electrons transfer, which could facilitate surface reaction process and boost the photocatalytic performance.
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Affiliation(s)
- Ran Chen
- Key Laboratory of Environmental Detection and Pollution Prevention, College of Life & Environmental Sciences, Huangshan University, Huangshan, 245041, PR, China.
| | - Bo Xu
- Key Laboratory of Environmental Detection and Pollution Prevention, College of Life & Environmental Sciences, Huangshan University, Huangshan, 245041, PR, China
| | - Heping Cheng
- School of Information Engineering, Huangshan University, Huangshan, 245041, China; State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, PR, China
| | - Qianqian Fang
- Key Laboratory of Environmental Detection and Pollution Prevention, College of Life & Environmental Sciences, Huangshan University, Huangshan, 245041, PR, China
| | - Minghai Ma
- Key Laboratory of Environmental Detection and Pollution Prevention, College of Life & Environmental Sciences, Huangshan University, Huangshan, 245041, PR, China
| | - Liping Qian
- Key Laboratory of Environmental Detection and Pollution Prevention, College of Life & Environmental Sciences, Huangshan University, Huangshan, 245041, PR, China
| | - Shunli Wan
- Key Laboratory of Environmental Detection and Pollution Prevention, College of Life & Environmental Sciences, Huangshan University, Huangshan, 245041, PR, China
| | - Shengyou Xu
- Key Laboratory of Environmental Detection and Pollution Prevention, College of Life & Environmental Sciences, Huangshan University, Huangshan, 245041, PR, China
| | - Yan Li
- Key Laboratory of Environmental Detection and Pollution Prevention, College of Life & Environmental Sciences, Huangshan University, Huangshan, 245041, PR, China
| | - Lei Zhang
- School of Environmental Science and Engineering, Yancheng Institute of Technology, Yancheng, 224051, PR, China.
| | - Shikai Xiang
- National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang, 621999, PR, China.
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2
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Stockerl WJ, Gschwind RM. Photo enhancement reveals ( E, Z) and ( Z, Z) configurations as additional intermediates in iminium ion catalysis. Chem Commun (Camb) 2023; 59:1325-1328. [PMID: 36644931 DOI: 10.1039/d2cc05976b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Imidazolidinone-based α,β-unsaturated iminium ions are the reactive species within countless synthetic protocols in asymmetric organocatalysis. However, (E,Z) and (Z,Z) imidazolidinone iminium ions, i.e. (Z)-CC configurations, have been elusive so far. Herein we describe how in situ photoisomerization enables the observation and assignment of high energetic (Z)-configured intermediates below the detection limit of NMR spectroscopy for (E,Z) and (Z,Z) iminium perchlorate complexes derived from MacMillan's 1st generation catalyst and cinnamaldehyde. Traces of (E,Z) could even be detected under synthetic conditions at 25 °C in MeCN. Using back isomerization studies and diffusion ordered spectroscopy, conditions were found to stabilize the (E,Z) and (Z,Z) isomers for several hours via ion pair aggregation. Thus, at least (E,Z) should be considered for future investigations in asymmetric iminium ion catalysis.
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Affiliation(s)
- Willibald J Stockerl
- Institute of Organic Chemistry, University of Regensburg, 93040, Regensburg, Germany.
| | - Ruth M Gschwind
- Institute of Organic Chemistry, University of Regensburg, 93040, Regensburg, Germany.
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3
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Gramüller J, Franta M, Gschwind RM. Tilting the Balance: London Dispersion Systematically Enhances Enantioselectivities in Brønsted Acid Catalyzed Transfer Hydrogenation of Imines. J Am Chem Soc 2022; 144:19861-19871. [PMID: 36260790 DOI: 10.1021/jacs.2c07563] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
London dispersion (LD) is attracting more and more attention in catalysis since LD is ubiquitously present and cumulative. Since dispersion is hard to grasp, recent research has concentrated mainly on the effect of LD in individual catalytic complexes or on the impact of dispersion energy donors (DEDs) on balance systems. The systematic transfer of LD effects onto confined and more complex systems in catalysis is still in its infancy, and no general approach for using DED residues in catalysis has emerged so far. Thus, on the example of asymmetric Brønsted acid catalyzed transfer hydrogenation of imines, we translated the findings of previously isolated balance systems onto confined catalytic intermediates, resulting in a systematic enhancement of stereoselectivity when employing DED-substituted substrates. As the imine substrate is present as Z- and E-isomers, which can, respectively, be converted to R- and S-product enantiomers, implementing tert-butyl groups as DED residues led to an additional stabilization of the Z-imine by up to 4.5 kJ/mol. NMR studies revealed that this effect is transferred onto catalyst/imine and catalyst/imine/nucleophile intermediates and that the underlying reaction mechanism is not affected. A clear correlation between ee and LD stabilization was demonstrated for 3 substrates and 10 catalysts, allowing to convert moderate-good to good-excellent enantioselectivities. Our findings conceptualize a general approach on how to beneficially employ DED residues in catalysis: they clearly showcase that bulky alkyl residues such as tert-butyl groups must be considered regarding not only their repulsive steric bulk but also their attractive properties even in catalytic complexes.
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Affiliation(s)
- Johannes Gramüller
- Institute of Organic Chemistry, University of Regensburg, 93040 Regensburg, Germany
| | - Maximilian Franta
- Institute of Organic Chemistry, University of Regensburg, 93040 Regensburg, Germany
| | - Ruth M Gschwind
- Institute of Organic Chemistry, University of Regensburg, 93040 Regensburg, Germany
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4
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Substrate Photoswitching for Rate Enhancement of an Organocatalytic Cyclization Reaction. European J Org Chem 2022. [DOI: 10.1002/ejoc.202200048] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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5
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Žabka M, Gschwind RM. Ternary complexes of chiral disulfonimides in transfer-hydrogenation of imines: the relevance of late intermediates in ion pair catalysis. Chem Sci 2021; 12:15263-15272. [PMID: 34976346 PMCID: PMC8635212 DOI: 10.1039/d1sc03724b] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Accepted: 10/22/2021] [Indexed: 01/29/2023] Open
Abstract
In ion pairing catalysis, the structures of late intermediates and transition states are key to understanding and further development of the field. Typically, a plethora of transition states is explored computationally. However, especially for ion pairs the access to energetics via computational chemistry is difficult and experimental data is rare. Here, we present for the first time extensive NMR spectroscopic insights about the ternary complex of a catalyst, substrate, and reagent in ion pair catalysis exemplified by chiral Brønsted acid-catalyzed transfer hydrogenation. Quantum chemistry calculations were validated by a large amount of NMR data for the structural and energetic assessment of binary and ternary complexes. In the ternary complexes, the expected catalyst/imine H-bond switches to an unexpected O-H-N structure, not yet observed in the multiple hydrogen-bond donor-acceptor situation such as disulfonimides (DSIs). This arrangement facilitates the hydride transfer from the Hantzsch ester in the transition states. In these reactions with very high isomerization barriers preventing fast pre-equilibration, the reaction barriers from the ternary complex to the transition states determine the enantioselectivity, which deviates from the relative transition state energies. Overall, the weak hydrogen bonding, the hydrogen bond switching and the special geometrical adaptation of substrates in disulfonimide catalyst complexes explain the robustness towards more challenging substrates and show that DSIs have the potential to combine high flexibility and high stereoselectivity.
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Affiliation(s)
- Matej Žabka
- Institute of Organic Chemistry, University of Regensburg D-93053 Regensburg Germany
| | - Ruth M Gschwind
- Institute of Organic Chemistry, University of Regensburg D-93053 Regensburg Germany
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6
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Shoja A, Zhai J, Reid JP. Comprehensive Stereochemical Models for Selectivity Prediction in Diverse Chiral Phosphate-Catalyzed Reaction Space. ACS Catal 2021. [DOI: 10.1021/acscatal.1c03520] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Ali Shoja
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
| | - Jianyu Zhai
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
| | - Jolene P. Reid
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
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7
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Antenucci A, Dughera S, Renzi P. Green Chemistry Meets Asymmetric Organocatalysis: A Critical Overview on Catalysts Synthesis. CHEMSUSCHEM 2021; 14:2785-2853. [PMID: 33984187 PMCID: PMC8362219 DOI: 10.1002/cssc.202100573] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 04/30/2021] [Indexed: 05/30/2023]
Abstract
Can green chemistry be the right reading key to let organocatalyst design take a step forward towards sustainable catalysis? What if the intriguing chemistry promoted by more engineered organocatalysts was carried on by using renewable and naturally occurring molecular scaffolds, or at least synthetic catalysts more respectful towards the principles of green chemistry? Within the frame of these questions, this Review will tackle the most commonly occurring organic chiral catalysts from the perspective of their synthesis rather than their employment in chemical methodologies or processes. A classification of the catalyst scaffolds based on their E factor will be provided, and the global E factor (EG factor) will be proposed as a new green chemistry metric to consider, also, the synthetic route to the catalyst within a given organocatalytic process.
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Affiliation(s)
- Achille Antenucci
- Department of ChemistryUniversity of TurinVia Pietro Giuria, 710125TurinItaly
- NIS Interdeprtmental CentreINSTM Reference CentreUniversity of TurinVia Gioacchino Quarello 15/A10135TurinItaly
| | - Stefano Dughera
- Department of ChemistryUniversity of TurinVia Pietro Giuria, 710125TurinItaly
| | - Polyssena Renzi
- Department of ChemistryUniversity of TurinVia Pietro Giuria, 710125TurinItaly
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8
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Dreier C, Prädel L, Ehrhard AA, Wagner M, Hunger J. Association Equilibria of Organo-Phosphoric Acids with Imines from a Combined Dielectric and Nuclear Magnetic Resonance Spectroscopy Approach. Anal Chem 2021; 93:3914-3921. [PMID: 33600142 PMCID: PMC7931174 DOI: 10.1021/acs.analchem.0c04669] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Accepted: 02/08/2021] [Indexed: 11/29/2022]
Abstract
Aggregates formed between organo-phosphoric acids and imine bases in aprotic solvents are the reactive intermediates in Brønsted acid organo-catalysis. Due to the strong hydrogen-bonding interaction of the acids in solution, multiple homo- and heteroaggregates are formed with profound effects on catalytic activity. Yet, due to the similar binding motifs-hydrogen-bonds-it is challenging to experimentally quantify the abundance of these aggregates in solution. Here we demonstrate that a combination of nuclear magnetic resonance (NMR) and dielectric relaxation spectroscopy (DRS) allows for accurate speciation of these aggregates in solution. We show that only by using the observables of both experiments heteroaggregates can be discriminated with simultaneously taking homoaggregation into account. Comparison of the association of diphenyl phosphoric acid and quinaldine or phenylquinaline in chloroform, dichloromethane, or tetrahydrofuran suggests that the basicity of the base largely determines the association of one acid and one base molecule to form an ion-pair. We find the ion-pair formation constants to be highest in chloroform, slightly lower in dichloromethane and lowest in tetrahydrofuran, which indicates that the hydrogen-bonding ability of the solvent also alters ion-pairing equilibria. We find evidence for the formation of multimers, consisting of one imine base and multiple diphenyl phosphoric acid molecules for both bases in all three solvents. This subsequent association of an acid to an ion-pair is however little affected by the nature of the base or the solvent. As such our findings provide routes to enhance the overall fraction of these multimers in solution, which have been reported to open new catalytic pathways.
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Affiliation(s)
- Christian Dreier
- Max
Planck Institute for Polymer Research, Department for Molecular Spectroscopy, Ackermannweg 10, 55128 Mainz, Germany
| | - Leon Prädel
- Max
Planck Institute for Polymer Research, Department for Molecular Spectroscopy, Ackermannweg 10, 55128 Mainz, Germany
| | - Amelie A. Ehrhard
- Max
Planck Institute for Polymer Research, Department for Molecular Spectroscopy, Ackermannweg 10, 55128 Mainz, Germany
| | - Manfred Wagner
- Max
Planck Institute for Polymer Research, Department for Molecular Spectroscopy, Ackermannweg 10, 55128 Mainz, Germany
| | - Johannes Hunger
- Max
Planck Institute for Polymer Research, Department for Molecular Spectroscopy, Ackermannweg 10, 55128 Mainz, Germany
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9
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Skubi KL, Swords WB, Hofstetter H, Yoon TP. LED-NMR Monitoring of an Enantioselective Catalytic [2+2] Photocycloaddition. CHEMPHOTOCHEM 2020; 4:685-690. [PMID: 34532566 PMCID: PMC8443221 DOI: 10.1002/cptc.202000094] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Indexed: 01/08/2023]
Abstract
We report that an NMR spectrometer equipped with a high-power LED light source can be used to study a fast enantioselective photocatalytic [2+2] cycloaddition. While traditional ex situ applications of NMR provide considerable information on reaction mechanisms, they are often ineffective for observing fast reactions. Recently, motivated by renewed interest in organic photochemistry, several approaches have been reported for in situ monitoring of photochemical reactions. These previously disclosed methods, however, have rarely been applied to rapid (<5 min) photochemical reactions. Furthermore, these approaches have not previously been used to interrogate the mechanisms of photocatalytic energy-transfer reactions. In the present work, we describe our experimental setup and demonstrate its utility by determining a phenomenological rate law for a model photocatalytic energy-transfer cycloaddition reaction.
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Affiliation(s)
- Kazimer L Skubi
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI (USA)
- Department of Chemistry, Skidmore College, 815 North Broadway, Saratoga Springs, NY (USA)
| | - Wesley B Swords
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI (USA)
| | - Heike Hofstetter
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI (USA)
| | - Tehshik P Yoon
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI (USA)
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10
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Niedek D, Erb FR, Topp C, Seitz A, Wende RC, Eckhardt AK, Kind J, Herold D, Thiele CM, Schreiner PR. In Situ Switching of Site-Selectivity with Light in the Acetylation of Sugars with Azopeptide Catalysts. J Org Chem 2020; 85:1835-1846. [PMID: 31763833 DOI: 10.1021/acs.joc.9b01913] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
We present a novel concept for the in situ control of site-selectivity of catalytic acetylations of partially protected sugars using light as external stimulus and oligopeptide catalysts equipped with an azobenzene moiety. The isomerizable azobenzene-peptide backbone defines the size and shape of the catalytic pocket, while the π-methyl-l-histidine (Pmh) moiety transfers the electrophile. Photoisomerization of the E- to the Z-azobenzene catalyst (monitored via NMR) with an LED (λ = 365 nm) drastically changes the chemical environment around the catalytically active Pmh moiety, so that the light-induced change in the catalyst shape alters site-selectivity. As a proof of principle, we employed (4,6-O-benzylidene)methyl-α-d-pyranosides, which provide a change in regioselectivity from 2:1 (E) to 1:5 (Z) for the monoacetylated products at room temperature. The validity of this new catalyst-design concept is further demonstrated with the regioselective acetylation of the natural product quercetin. In situ irradiation NMR spectroscopy was used to quantify photostationary states under continuous irradiation with UV light.
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Affiliation(s)
- Dominik Niedek
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - Frederik R Erb
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - Christopher Topp
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - Alexander Seitz
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - Raffael C Wende
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - André K Eckhardt
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
| | - Jonas Kind
- Clemens-Schöpf-Institut für Organische Chemie und Biochemie , Technische Universität Darmstadt , Alarich-Weiss-Str. 16 , 64287 Darmstadt , Germany
| | - Dominik Herold
- Clemens-Schöpf-Institut für Organische Chemie und Biochemie , Technische Universität Darmstadt , Alarich-Weiss-Str. 16 , 64287 Darmstadt , Germany
| | - Christina M Thiele
- Clemens-Schöpf-Institut für Organische Chemie und Biochemie , Technische Universität Darmstadt , Alarich-Weiss-Str. 16 , 64287 Darmstadt , Germany
| | - Peter R Schreiner
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17 , 35392 Giessen , Germany
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11
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Onneken C, Bussmann K, Gilmour R. Inversion externer asymmetrischer Induktion durch selektive Energietransfer‐Katalyse: Strategie zu β‐chiralen Phosphonat‐Antipoden. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201911651] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- Carina Onneken
- Organisch Chemisches Institut Westfälische Wilhelms-Universität Münster Corrensstraße 40 48149 Münster Deutschland
| | - Kathrin Bussmann
- Organisch Chemisches Institut Westfälische Wilhelms-Universität Münster Corrensstraße 40 48149 Münster Deutschland
| | - Ryan Gilmour
- Organisch Chemisches Institut Westfälische Wilhelms-Universität Münster Corrensstraße 40 48149 Münster Deutschland
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12
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Onneken C, Bussmann K, Gilmour R. Inverting External Asymmetric Induction via Selective Energy Transfer Catalysis: A Strategy to β-Chiral Phosphonate Antipodes. Angew Chem Int Ed Engl 2019; 59:330-334. [PMID: 31617957 PMCID: PMC6972697 DOI: 10.1002/anie.201911651] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Indexed: 11/21/2022]
Abstract
Enantiodivergent, catalytic reduction of activated alkenes relays stereochemical information encoded in the antipodal chiral catalysts to the pro‐chiral substrate. Although powerful, the strategy remains vulnerable to costs and availability of sourcing both catalyst enantiomers. Herein, a stereodivergent hydrogenation of α,β‐unsaturated phosphonates is disclosed using a single enantiomer of the catalyst. This enables generation of the R‐ or S‐configured β‐chiral phosphonate with equal and opposite selectivity. Enantiodivergence is regulated at the substrate level through the development of a facile E → Z isomerisation. This has been enabled for the first time by selective energy transfer catalysis using anthracene as an inexpensive organic photosensitiser. Synthetically valuable in its own right, this process enables subsequent RhI‐mediated stereospecific hydrogenation to generate both enantiomers of the product using only the S‐catalyst (up to 99:1 and 3:97 e.r.). This strategy out‐competes the selectivities observed with the E‐substrate and the R‐catalyst.
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Affiliation(s)
- Carina Onneken
- Organisch Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149, Münster, Germany
| | - Kathrin Bussmann
- Organisch Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149, Münster, Germany
| | - Ryan Gilmour
- Organisch Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149, Münster, Germany
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13
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Rothermel K, Žabka M, Hioe J, Gschwind RM. Disulfonimides versus Phosphoric Acids in Brønsted Acid Catalysis: The Effect of Weak Hydrogen Bonds and Multiple Acceptors on Complex Structures and Reactivity. J Org Chem 2019; 84:13221-13231. [PMID: 31550152 PMCID: PMC6863592 DOI: 10.1021/acs.joc.9b01811] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Indexed: 12/20/2022]
Abstract
In Brønsted acid catalysis, hydrogen bonds play a crucial role for reactivity and selectivity. However, the contribution of weak hydrogen bonds or multiple acceptors has been unclear so far since it is extremely difficult to collect experimental evidence for weak hydrogen bonds. Here, our hydrogen bond and structural access to Brønsted acid/imine complexes was used to analyze BINOL-derived chiral disulfonimide (DSI)/imine complexes. 1H and 15N chemical shifts as well as 1JNH coupling constants revealed for DSI/imine complexes ion pairs with very weak hydrogen bonds. The high acidity of the DSIs leads to a significant weakening of the hydrogen bond as structural anchor. In addition, the five hydrogen bond acceptors of DSI allow an enormous mobility of the imine in the binary DSI complexes. Theoretical calculations predict the hydrogen bonds to oxygen to be energetically less favored; however, their considerable population is corroborated experimentally by NOE and exchange data. Furthermore, an N-alkylimine, which shows excellent reactivity and selectivity in reactions with DSI, reveals an enlarged structural space in complexes with the chiral phosphoric acid TRIP as potential explanation of its reduced reactivity and selectivity. Thus, considering factors such as flexibility and possible hydrogen bond sites is essential for catalyst development in Brønsted acid catalysis.
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Affiliation(s)
| | | | - Johnny Hioe
- Institute of Organic Chemistry, University of Regensburg, D-93053 Regensburg, Germany
| | - Ruth M. Gschwind
- Institute of Organic Chemistry, University of Regensburg, D-93053 Regensburg, Germany
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14
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Lokesh N, Hioe J, Gramüller J, Gschwind RM. Relaxation Dispersion NMR to Reveal Fast Dynamics in Brønsted Acid Catalysis: Influence of Sterics and H-Bond Strength on Conformations and Substrate Hopping. J Am Chem Soc 2019; 141:16398-16407. [PMID: 31545037 PMCID: PMC6863621 DOI: 10.1021/jacs.9b07841] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Indexed: 12/25/2022]
Abstract
NMR provides both structural and dynamic information, which is key to connecting intermediates and to understanding reaction pathways. However, fast exchanging catalytic intermediates are often inaccessible by conventional NMR due its limited time resolution. Here, we show the combined application of the 1H off-resonance R1ρ NMR method and low temperature (185-175 K) to resolve intermediates exchanging on a μs time scale (ns at room temperature). The potential of the approach is demonstrated on chiral phosphoric acid (CPA) catalysts in their complexes with imines. The otherwise inaccessible exchange kinetics of the E-I ⇌ E-II imine conformations and thermodynamic E-I:E-II imine ratios inside the catalyst pocket are experimentally determined and corroborated by calculations. The E-I ⇌ E-II exchange rate constants (kex185 K) for different catalyst-substrate binary complexes varied between 2500 and 19 000 s-1 (τex = 500-50 μs). Theoretical analysis of these exchange rate constants revealed the involvement of an intermediary tilted conformation E-III, which structurally resembles the hydride transfer transition state. The main E-I and E-II exchange pathway is a hydrogen bond strength dependent tilting-switching-tilting mechanism via a bifurcated hydrogen bond as a transition state. The reduction in the sterics of the catalyst showed an accelerated switching process by at least an order of magnitude and enabled an additional rotational pathway. Hence, the exchange process is mainly a function of the intrinsic properties of the 3,3'-substituents of the catalyst. Overall, we believe that the present study opens a new dimension in catalysis via experimental access to structures, populations, and kinetics of catalyst-substrate complexes on the μs time scale by the 1H off-resonance R1ρ method.
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Affiliation(s)
- N. Lokesh
- Institute of Organic Chemistry, University of Regensburg, D-93053 Regensburg, Germany
| | - Johnny Hioe
- Institute of Organic Chemistry, University of Regensburg, D-93053 Regensburg, Germany
| | - Johannes Gramüller
- Institute of Organic Chemistry, University of Regensburg, D-93053 Regensburg, Germany
| | - Ruth M. Gschwind
- Institute of Organic Chemistry, University of Regensburg, D-93053 Regensburg, Germany
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15
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Nitschke P, Lokesh N, Gschwind RM. Combination of illumination and high resolution NMR spectroscopy: Key features and practical aspects, photochemical applications, and new concepts. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2019; 114-115:86-134. [PMID: 31779887 DOI: 10.1016/j.pnmrs.2019.06.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Revised: 06/04/2019] [Accepted: 06/04/2019] [Indexed: 06/10/2023]
Abstract
In the last decade, photochemical and photocatalytic applications have developed into one of the dominant research fields in chemistry. However, mechanistic investigations to sustain this enormous progress are still relatively sparse and in high demand by the photochemistry community. UV/Vis spectroscopy and EPR spectroscopy have been the main spectroscopic tools to study the mechanisms of photoreactions due to their higher time resolution and sensitivity. On the other hand, application of NMR in photosystems has been mainly restricted to photo-CIDNP, since the initial photoexcitation was thought to be the single key to understand photoinduced reactions. In 2015 the Gschwind group showcased the possibility that different reaction pathways could occur from the same photoexcited state depending on the reaction conditions by using in situ LED illumination NMR. This was the starting point to push the active participation of NMR in photosystems to its full potential, including reaction profiling, structure determination of intermediates, downstream mechanistic studies, dark pathways, intermediate sequencing with CEST etc. Following this, multiple studies using in situ illumination NMR have been reported focusing on mechanistic investigations in photocatalysis, photoswitches, and polymerizations. The recent increased popularity of this technique can be attributed to the simplicity of the experimental setup and the availability of low cost, high power LEDs. Here, we review the development of experimental design, applications and new concepts of illuminated NMR. In the first part, we describe the development of different designs of NMR illumination apparatus, illuminating from the bottom/side/top/inside, and discuss their pros and cons for specific applications. Furthermore, we address LASERs and LEDs as different light sources as well as special cases such as UVNMR(-illumination), FlowNMR, NMR on a Chip etc. To complete the discussion on experimental apparatus, the advantages and disadvantages of in situ LED illumination NMR versus ex situ illumination NMR are described. The second part of this review discusses different facets of applications of inside illumination experiments. It highlights newly revealed mechanistic and structural information and ideas in the fields of photocatalyis, photoswitches and photopolymerization. Finally, we present new concepts and methods based on the combination of NMR and illumination such as sensitivity enhancement, chemical pump probes, experimental access to transition state combinations and NMR actinometry. Overall this review presents NMR spectroscopy as a complementary tool to UV/Vis spectroscopy in mechanistic and structural investigations of photochemical processes. The review is presented in a way that is intended to assist the photochemistry and photocatalysis community in adopting and understanding this astonishingly powerful in situ LED illumination NMR method for their investigations on a daily basis.
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Affiliation(s)
- Philipp Nitschke
- Organic Chemistry, University of Regensburg, 93040 Regensburg, Germany
| | | | - Ruth M Gschwind
- Organic Chemistry, University of Regensburg, 93040 Regensburg, Germany.
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16
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Lundrigan T, Welsh EN, Hynes T, Tien CH, Adams MR, Roy KR, Robertson KN, Speed AWH. Enantioselective Imine Reduction Catalyzed by Phosphenium Ions. J Am Chem Soc 2019; 141:14083-14088. [PMID: 31441650 DOI: 10.1021/jacs.9b07293] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The first use of phosphenium cations in asymmetric catalysis is reported. A diazaphosphenium triflate, prepared in two or three steps on a multigram scale from commercially available materials, catalyzes the hydroboration or hydrosilylation of cyclic imines with enantiomeric ratios of up to 97:3. Catalyst loadings are as low as 0.2 mol %. Twenty-two aryl/heteroaryl pyrrolidines and piperidines were prepared using this method. Imines containing functional groups such as thiophenes or pyridyl rings that can challenge transition-metal catalysts were reduced employing these systems.
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Affiliation(s)
- Travis Lundrigan
- Department of Chemistry , Dalhousie University , Halifax , Nova Scotia , Canada B3H 4R2
| | - Erin N Welsh
- Department of Chemistry , Dalhousie University , Halifax , Nova Scotia , Canada B3H 4R2
| | - Toren Hynes
- Department of Chemistry , Dalhousie University , Halifax , Nova Scotia , Canada B3H 4R2
| | - Chieh-Hung Tien
- Department of Chemistry , Dalhousie University , Halifax , Nova Scotia , Canada B3H 4R2
| | - Matt R Adams
- Department of Chemistry , Dalhousie University , Halifax , Nova Scotia , Canada B3H 4R2
| | - Kayelani R Roy
- Department of Chemistry , Dalhousie University , Halifax , Nova Scotia , Canada B3H 4R2
| | - Katherine N Robertson
- Department of Chemistry , Saint Mary's University , Halifax , Nova Scotia , Canada B3H 3C3
| | - Alexander W H Speed
- Department of Chemistry , Dalhousie University , Halifax , Nova Scotia , Canada B3H 4R2
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17
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Rothermel K, Melikian M, Hioe J, Greindl J, Gramüller J, Žabka M, Sorgenfrei N, Hausler T, Morana F, Gschwind RM. Internal acidity scale and reactivity evaluation of chiral phosphoric acids with different 3,3'-substituents in Brønsted acid catalysis. Chem Sci 2019; 10:10025-10034. [PMID: 32015815 PMCID: PMC6977555 DOI: 10.1039/c9sc02342a] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Accepted: 09/02/2019] [Indexed: 12/16/2022] Open
Abstract
NMR H-bond analysis reveals an offset of internal and external acidities of catalysts and allows for a detailed reactivity analysis.
The concept of hydrogen bonding for enhancing substrate binding and controlling selectivity and reactivity is central in catalysis. However, the properties of these key hydrogen bonds and their catalyst-dependent variations are extremely difficult to determine directly by experiments. Here, for the first time the hydrogen bond properties of a whole series of BINOL-derived chiral phosphoric acid (CPA) catalysts in their substrate complexes with various imines were investigated to derive the influence of different 3,3′-substituents on the acidity and reactivity. NMR 1H and 15N chemical shifts and 1JNH coupling constants of these hydrogen bonds were used to establish an internal acidity scale corroborated by calculations. Deviations from calculated external acidities reveal the importance of intermolecular interactions for this key feature of CPAs. For CPAs with similarly sized binding pockets, a correlation of reactivity and hydrogen bond strengths of the catalyst was found. A catalyst with a very small binding pocket showed significantly reduced reactivities. Therefore, NMR isomerization kinetics, population and chemical shift analyses of binary and ternary complexes as well as reaction kinetics were performed to address the steps of the transfer hydrogenation influencing the overall reaction rate. The results of CPAs with different 3,3′-substituents show a delicate balance between the isomerization and the ternary complex formation to be rate-determining. For CPAs with an identical acidic motif and similar sterics, reactivity and internal acidity correlated inversely. In cases where higher sterical demand within the binary complex hinders the binding of the second substrate, the correlation between acidity and reactivity breaks down.
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Affiliation(s)
- Kerstin Rothermel
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
| | - Maxime Melikian
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
| | - Johnny Hioe
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
| | - Julian Greindl
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
| | - Johannes Gramüller
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
| | - Matej Žabka
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
| | - Nils Sorgenfrei
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
| | - Thomas Hausler
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
| | - Fabio Morana
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
| | - Ruth M Gschwind
- Institut für Organische Chemie , Universität Regensburg , Universitätsstraße 31 , D-93053 Regensburg , Germany .
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Ji Y, DiRocco DA, Kind J, Thiele CM, Gschwind RM, Reibarkh M. LED‐Illuminated NMR Spectroscopy: A Practical Tool for Mechanistic Studies of Photochemical Reactions. CHEMPHOTOCHEM 2019. [DOI: 10.1002/cptc.201900109] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Yining Ji
- Process Research & DevelopmentMerck & Co., Inc. Rahway New Jersey 07065 USA
| | - Daniel A. DiRocco
- Process Research & DevelopmentMerck & Co., Inc. Rahway New Jersey 07065 USA
| | - Jonas Kind
- Clemens-Schöpf-Institut für Organische Chemie und BiochemieTechnische Universität Darmstadt Alarich-Weiss-Str. 16 64287 Darmstadt Germany
| | - Christina M. Thiele
- Clemens-Schöpf-Institut für Organische Chemie und BiochemieTechnische Universität Darmstadt Alarich-Weiss-Str. 16 64287 Darmstadt Germany
| | - Ruth M. Gschwind
- Institute of Organic ChemistryUniversity of Regensburg Universitätsstrasse 31 93053 Regensburg Germany
| | - Mikhail Reibarkh
- Process Research & DevelopmentMerck & Co., Inc. Rahway New Jersey 07065 USA
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19
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Lehnherr D, Ji Y, Neel AJ, Cohen RD, Brunskill APJ, Yang J, Reibarkh M. Discovery of a Photoinduced Dark Catalytic Cycle Using in Situ LED-NMR Spectroscopy. J Am Chem Soc 2018; 140:13843-13853. [DOI: 10.1021/jacs.8b08596] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Dan Lehnherr
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Yining Ji
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Andrew J. Neel
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Ryan D. Cohen
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Andrew P. J. Brunskill
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Junyu Yang
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Mikhail Reibarkh
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
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20
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Ramanathan M, Wang YH, Liu YH, Peng SM, Cheng YC, Liu ST. Preparation of Ketimines from Aryldiazonium Salts, Arenes, and Nitriles via Intermolecular Arylation of N-Arylnitrilium Ions. J Org Chem 2018; 83:6133-6141. [PMID: 29732894 DOI: 10.1021/acs.joc.8b01000] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A transition-metal-free approach for the preparation of N-arylketimines has been developed from the direct reaction of aryldiazonium salts, arenes, and nitriles in a one-pot fashion with the consecutive formation of N-C and C-C bonds. This approach proceeds via an in situ generation of N-arylnitrilium intermediate, which then undergoes intermolecular arylation. This three-component strategy offers a step- and atom-efficient way to N-arylketimines from easily accessible reagents under mild reaction conditions. The characterization of stereochemistry of ketimine was achieved by X-ray crystallographic structure and theoretical calculation. Operational simplicity, shorter reaction time, excellent functional group compatibility, and scalability are the key features of this report.
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Affiliation(s)
- Mani Ramanathan
- Department of Chemistry , National Taiwan University , Taipei 106 , Taiwan
| | - Yu-Hao Wang
- Department of Chemistry , National Taiwan University , Taipei 106 , Taiwan
| | - Yi-Hung Liu
- Department of Chemistry , National Taiwan University , Taipei 106 , Taiwan
| | - Shie-Ming Peng
- Department of Chemistry , National Taiwan University , Taipei 106 , Taiwan
| | - Yuan-Chung Cheng
- Department of Chemistry , National Taiwan University , Taipei 106 , Taiwan
| | - Shiuh-Tzung Liu
- Department of Chemistry , National Taiwan University , Taipei 106 , Taiwan
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21
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Simón L, Paton RS. The True Catalyst Revealed: The Intervention of Chiral Ca and Mg Phosphates in Brønsted Acid Promoted Asymmetric Mannich Reactions. J Am Chem Soc 2018; 140:5412-5420. [DOI: 10.1021/jacs.7b13678] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Luis Simón
- Facultad de Ciencias Químicas, Universidad de Salamanca, Plaza de los Caídos 1-5, Salamanca 37008, Spain
| | - Robert S. Paton
- Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
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22
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Ji Y, DiRocco DA, Hong CM, Wismer MK, Reibarkh M. Facile Quantum Yield Determination via NMR Actinometry. Org Lett 2018; 20:2156-2159. [DOI: 10.1021/acs.orglett.8b00391] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yining Ji
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065 United States
| | - Daniel A. DiRocco
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065 United States
| | - Cynthia M. Hong
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065 United States
- Chemical Sciences Division, Lawrence Berkeley National Laboratory and Department of Chemistry, University of California, Berkeley, California 94720 United States
| | - Michael K. Wismer
- Scientific Engineering and Design, Merck & Co., Inc., Rahway, New Jersey 07065 United States
| | - Mikhail Reibarkh
- Process Research & Development, Merck & Co., Inc., Rahway, New Jersey 07065 United States
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Pèrez-Miqueo J, San Nacianceno V, Urquiola FB, Freixa Z. Revisiting the iridacycle-catalyzed hydrosilylation of enolizable imines. Catal Sci Technol 2018. [DOI: 10.1039/c8cy01236a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
In situ1H NMR spectroscopy reveals a cascade mechanism for the hydrosilylation of enolizable imines catalyzed by iridium(iii) metallacycles.
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Affiliation(s)
- Jorge Pèrez-Miqueo
- Department of Applied Chemistry
- Faculty of Chemistry
- University of the Basque Country (UPV-EHU)
- San Sebastián
- Spain
| | - Virginia San Nacianceno
- Department of Applied Chemistry
- Faculty of Chemistry
- University of the Basque Country (UPV-EHU)
- San Sebastián
- Spain
| | - F. Borja Urquiola
- Department of Applied Chemistry
- Faculty of Chemistry
- University of the Basque Country (UPV-EHU)
- San Sebastián
- Spain
| | - Zoraida Freixa
- Department of Applied Chemistry
- Faculty of Chemistry
- University of the Basque Country (UPV-EHU)
- San Sebastián
- Spain
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24
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Renzi P, Hioe J, Gschwind RM. Enamine/Dienamine and Brønsted Acid Catalysis: Elusive Intermediates, Reaction Mechanisms, and Stereoinduction Modes Based on in Situ NMR Spectroscopy and Computational Studies. Acc Chem Res 2017; 50:2936-2948. [PMID: 29172479 PMCID: PMC6300316 DOI: 10.1021/acs.accounts.7b00320] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
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Over the years, the field of enantioselective organocatalysis has
seen unparalleled growth in the development of novel synthetic applications
with respect to mechanistic investigations. Reaction optimization
appeared to be rather empirical than rational. This offset between
synthetic development and mechanistic understanding was and is generally
due to the difficulties in detecting reactive intermediates and the
inability to experimentally evaluate transition states. Thus, the
first key point for mechanistic studies is detecting elusive intermediates
and characterizing them in terms of their structure, stability, formation
pathways, and kinetic properties. The second key point is evaluating
the importance of these intermediates and their properties in the
transition state. In the past 7 years, our group has addressed
the problems with
detecting elusive intermediates in organocatalysis by means of NMR
spectroscopy and eventually theoretical calculations. Two main activation
modes were extensively investigated: secondary amine catalysis and,
very recently, Brønsted acid catalysis. Using these examples,
we discuss potential methods to stabilize intermediates via intermolecular
interactions; to elucidate their structures, formation pathways and
kinetics; to change the kinetics of the reactions; and to address
their relevance in transition states. The elusive enamine in proline-catalyzed
aldol reactions is used as an example of the stabilization of intermediates
via inter- and intramolecular interactions; the determination of kinetics
on its formation pathway is discussed. Classical structural characterization
of intermediates is described using prolinol and prolinol ether enamines
and dienamines. The Z/E dilemma
for the second double bond of the dienamines shows how the kinetics
of a reaction can be changed to allow for the detection of reaction
intermediates. We recently started to investigate substrate–catalyst
complexes in the field of Brønsted acid catalysis. These studies
on imine/chiral phosphoric acid complexes show that an appropriate
combination of highly developed NMR and theoretical methods can provide
detailed insights into the complicated structures, exchange kinetics,
and H-bonding properties of chiral ion pairs. Furthermore, the merging
of these structural investigations and photoisomerization even allowed
the active transition state combinations to be determined for the
first time on the basis of experimental data only, which is the gold
standard in mechanistic investigations and was previously thought
to be exclusively the domain of theoretical calculations. Thus,
this Account summarizes our recent mechanistic work in the
field of organocatalysis and explains the potential methods for addressing
the central questions in mechanistic studies: stabilization of intermediates,
elucidation of structures and formation pathways, and addressing transition
state combinations experimentally.
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Affiliation(s)
- Polyssena Renzi
- Institut für Organische Chemie, Universität Regensburg, D-95053 Regensburg, Germany
| | - Johnny Hioe
- Institut für Organische Chemie, Universität Regensburg, D-95053 Regensburg, Germany
| | - Ruth M. Gschwind
- Institut für Organische Chemie, Universität Regensburg, D-95053 Regensburg, Germany
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