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Paul M, Peckelsen K, Thomulka T, Martens J, Berden G, Oomens J, Neudörfl JM, Breugst M, Meijer AJHM, Schäfer M, Berkessel A. Breslow Intermediates (Amino Enols) and Their Keto Tautomers: First Gas-Phase Characterization by IR Ion Spectroscopy. Chemistry 2021; 27:2662-2669. [PMID: 32893891 PMCID: PMC7898712 DOI: 10.1002/chem.202003454] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Revised: 09/01/2020] [Indexed: 12/11/2022]
Abstract
Breslow intermediates (BIs) are the crucial nucleophilic amino enol intermediates formed from electrophilic aldehydes in the course of N-heterocyclic carbene (NHC)-catalyzed umpolung reactions. Both in organocatalytic and enzymatic umpolung, the question whether the Breslow intermediate exists as the nucleophilic enol or in the form of its electrophilic keto tautomer is of utmost importance for its reactivity and function. Herein, the preparation of charge-tagged Breslow intermediates/keto tautomers derived from three different types of NHCs (imidazolidin-2-ylidenes, 1,2,4-triazolin-5-ylidenes, thiazolin-2-ylidenes) and aldehydes is reported. An ammonium charge tag is introduced through the aldehyde unit or the NHC. ESI-MS IR ion spectroscopy allowed the unambiguous conclusion that in the gas phase, the imidazolidin-2-ylidene-derived BI indeed exists as a diamino enol, while both 1,2,4-triazolin-5-ylidenes and thiazolin-2-ylidenes give the keto tautomer. This result coincides with the tautomeric states observed for the BIs in solution (NMR) and in the crystalline state (XRD), and is in line with our earlier calculations on the energetics of BI keto-enol equilibria.
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Affiliation(s)
- Mathias Paul
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Katrin Peckelsen
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Thomas Thomulka
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Jonathan Martens
- Institute for Molecules and Materials, FELIX Laboratory, Radboud University, Toernooiveld 7, 6525, ED, Nijmegen, The Netherlands
| | - Giel Berden
- Institute for Molecules and Materials, FELIX Laboratory, Radboud University, Toernooiveld 7, 6525, ED, Nijmegen, The Netherlands
| | - Jos Oomens
- Institute for Molecules and Materials, FELIX Laboratory, Radboud University, Toernooiveld 7, 6525, ED, Nijmegen, The Netherlands.,Van' t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands
| | - Jörg-M Neudörfl
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Martin Breugst
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | | | - Mathias Schäfer
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
| | - Albrecht Berkessel
- Department of Chemistry, Cologne University, Greinstrasse 4, 50939, Cologne, Germany
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Paul M, Peckelsen K, Thomulka T, Martens J, Berden G, Oomens J, Neudörfl J, Breugst M, Meijer AJHM, Schäfer M, Berkessel A. Cover Feature: Breslow Intermediates (Amino Enols) and Their Keto Tautomers: First Gas‐Phase Characterization by IR Ion Spectroscopy (Chem. Eur. J. 8/2021). Chemistry 2021. [DOI: 10.1002/chem.202004678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Mathias Paul
- Department of Chemistry Cologne University Greinstrasse 4 50939 Cologne Germany
| | - Katrin Peckelsen
- Department of Chemistry Cologne University Greinstrasse 4 50939 Cologne Germany
| | - Thomas Thomulka
- Department of Chemistry Cologne University Greinstrasse 4 50939 Cologne Germany
| | - Jonathan Martens
- Institute for Molecules and Materials FELIX Laboratory Radboud University Toernooiveld 7 6525 ED Nijmegen The Netherlands
| | - Giel Berden
- Institute for Molecules and Materials FELIX Laboratory Radboud University Toernooiveld 7 6525 ED Nijmegen The Netherlands
| | - Jos Oomens
- Institute for Molecules and Materials FELIX Laboratory Radboud University Toernooiveld 7 6525 ED Nijmegen The Netherlands
- Van' t Hoff Institute for Molecular Sciences University of Amsterdam Science Park 904 1098 XH Amsterdam The Netherlands
| | - Jörg‐M. Neudörfl
- Department of Chemistry Cologne University Greinstrasse 4 50939 Cologne Germany
| | - Martin Breugst
- Department of Chemistry Cologne University Greinstrasse 4 50939 Cologne Germany
| | | | - Mathias Schäfer
- Department of Chemistry Cologne University Greinstrasse 4 50939 Cologne Germany
| | - Albrecht Berkessel
- Department of Chemistry Cologne University Greinstrasse 4 50939 Cologne Germany
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Paul M, Peckelsen K, Thomulka T, Neudörfl J, Martens J, Berden G, Oomens J, Berkessel A, Meijer AJHM, Schäfer M. Hydrogen tunneling avoided: enol-formation from a charge-tagged phenyl pyruvic acid derivative evidenced by tandem-MS, IR ion spectroscopy and theory. Phys Chem Chem Phys 2019; 21:16591-16600. [PMID: 31317140 DOI: 10.1039/c9cp02316j] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
A charge-tagged phenyl pyruvic acid derivative was investigated by tandem-MS, infrared (IR) ion spectroscopy and theory. The tailor-made precursor ions efficiently lose CO2 in collision induced dissociation (CID) experiments, offering access to study the secondary decay reactions of the product ions. IR ion spectroscopy provides evidence for the formation of an enol acid precursor ion structure in the gas phase and indicates the presence of enol products formed after CO2 loss. Extensive DFT computations however, suggest intermediate generation of hydroxycarbene products, which in turn rearrange in a secondary process to the enol ions detected by IR ion spectroscopy. Quantum mechanical tunneling of the hydroxycarbene can be excluded since no evidence for aldehyde product ion formation could be found. This finding is in contrast to the behavior of methylhydroxycarbene, which cleanly penetrates the energy barrier to form exclusively acetaldehyde at cryogenic temperatures in an argon matrix via quantum mechanical hydrogen tunneling. The results presented here are attributed to the highly excited energy levels of the product ions formed by CID in combination with different barrier heights of the competing reaction channels, which allow exclusive access over one energy barrier leading to the formation of the enol tautomer ions observed.
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Affiliation(s)
- Mathias Paul
- University of Cologne, Department of Chemistry, Greinstrasse 4, 50939 Köln, Germany.
| | - Katrin Peckelsen
- University of Cologne, Department of Chemistry, Greinstrasse 4, 50939 Köln, Germany.
| | - Thomas Thomulka
- University of Cologne, Department of Chemistry, Greinstrasse 4, 50939 Köln, Germany.
| | - Jörg Neudörfl
- University of Cologne, Department of Chemistry, Greinstrasse 4, 50939 Köln, Germany.
| | - Jonathan Martens
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands
| | - Giel Berden
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands
| | - Jos Oomens
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands and Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Albrecht Berkessel
- University of Cologne, Department of Chemistry, Greinstrasse 4, 50939 Köln, Germany.
| | | | - Mathias Schäfer
- University of Cologne, Department of Chemistry, Greinstrasse 4, 50939 Köln, Germany.
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Schäfer M, Peckelsen K, Paul M, Martens J, Oomens J, Berden G, Berkessel A, Meijer AJHM. Hydrogen Tunneling above Room Temperature Evidenced by Infrared Ion Spectroscopy. J Am Chem Soc 2017; 139:5779-5786. [PMID: 28282985 DOI: 10.1021/jacs.6b10348] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
While hydrogen tunneling at elevated temperatures has, for instance, often been postulated in biochemical processes, spectroscopic proof is thus far limited to cryogenic conditions, under which thermal reactivity is negligible. We report spectroscopic evidence for H-tunneling in the gas phase at temperatures around 320-350 K observed in the isomerization reaction of a hydroxycarbene into an aldehyde. The charge-tagged carbene was generated in situ in a tandem mass spectrometer by decarboxylation of oxo[4-(trimethylammonio)phenyl]acetic acid upon collision induced dissociation. All ion structures involved are characterized by infrared ion spectroscopy and quantum chemical calculations. The charge-tagged phenylhydroxycarbene undergoes a 1,2-H-shift to the corresponding aldehyde with an half-life of about 10 s, evidenced by isomer-selective two-color (IR-IR) spectroscopy. In contrast, the deuterated (OD) carbene analogue showed much reduced 1,2-D-shift reactivity with an estimated half-life of at least 200 s under the experimental conditions, and provides clear evidence for hydrogen atom tunneling in the H-isotopologue. This is the first spectroscopic confirmation of hydrogen atom tunneling governing 1,2-H-shift reactions at noncryogenic temperatures, which is of broad significance for a range of (bio)chemical processes, including enzymatic transformations and organocatalysis.
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Affiliation(s)
- Mathias Schäfer
- Department of Chemistry, Organic Chemistry, University of Cologne , Greinstraße 4, 50939 Cologne, Germany
| | - Katrin Peckelsen
- Department of Chemistry, Organic Chemistry, University of Cologne , Greinstraße 4, 50939 Cologne, Germany
| | - Mathias Paul
- Department of Chemistry, Organic Chemistry, University of Cologne , Greinstraße 4, 50939 Cologne, Germany
| | - Jonathan Martens
- Radboud University , Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands
| | - Jos Oomens
- Radboud University , Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands.,Van't Hoff Institute for Molecular Sciences, University of Amsterdam , Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Giel Berden
- Radboud University , Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands
| | - Albrecht Berkessel
- Department of Chemistry, Organic Chemistry, University of Cologne , Greinstraße 4, 50939 Cologne, Germany
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Peckelsen K, Martens J, Czympiel L, Oomens J, Berden G, Gründemann D, Meijer AJHM, Schäfer M. Ergothioneine and related histidine derivatives in the gas phase: tautomer structures determined by IRMPD spectroscopy and theory. Phys Chem Chem Phys 2017; 19:23362-23372. [DOI: 10.1039/c7cp03843g] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Gas-phase analysis of ergothioneine molecular ions allows differentiating thiol from thione tautomer structures.
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Affiliation(s)
- Katrin Peckelsen
- Department für Chemie
- Institut für Organische Chemie
- Universität zu Köln
- Greinstrasse 4
- Köln
| | - Jonathan Martens
- Radboud University
- Institute for Molecules and Materials
- FELIX Laboratory
- Toernooiveld 7c
- Nijmegen
| | - Lisa Czympiel
- Department für Chemie
- Institut für Organische Chemie
- Universität zu Köln
- Greinstrasse 4
- Köln
| | - Jos Oomens
- Radboud University
- Institute for Molecules and Materials
- FELIX Laboratory
- Toernooiveld 7c
- Nijmegen
| | - Giel Berden
- Radboud University
- Institute for Molecules and Materials
- FELIX Laboratory
- Toernooiveld 7c
- Nijmegen
| | - Dirk Gründemann
- Department of Pharmacology
- University of Cologne
- Gleueler Straße 24
- Cologne
- Germany
| | | | - Mathias Schäfer
- Department für Chemie
- Institut für Organische Chemie
- Universität zu Köln
- Greinstrasse 4
- Köln
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