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Miyajima R, Ooe Y, Miura T, Ikoma T, Iwamoto H, Takizawa SY, Hasegawa E. Triarylamine-Substituted Benzimidazoliums as Electron Donor-Acceptor Dyad-Type Photocatalysts for Reductive Organic Transformations. J Am Chem Soc 2023; 145:10236-10248. [PMID: 37127911 DOI: 10.1021/jacs.3c01264] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Triarylamine-substituted benzimidazoliums (BI+-PhNAr2), new electron donor-acceptor dyad molecules, were synthesized. Their photocatalytic properties for reductive organic transformations were explored using absorption and fluorescence spectroscopy, redox potential determinations, density functional theory calculations, transient absorption spectroscopy, and reduction reactions of selected substrates. The results show that irradiation of BI+-PhNAr2 promotes photoinduced intramolecular electron transfer to form a long-lived (∼300 μs) charge shifted state (BI•-PhN•+Ar2). In the pathway for photocatalysis of reduction reactions of substrates, BI•-PhN•+Ar2 is subsequently transformed to the neutral benzimidazolyl radical (BI•-PhNAr2) by single-electron transfer from the donor 1,3-dimethyl-2-phenylbenzimidazoline (BIH-Ph) serving as a cooperative agent. Among the benzimidazoliums explored, the bromo-substituted analogue BI+-PhN(C6H4Br-p)2 in conjunction with BIH-Ph demonstrates the most consistent catalytic performance.
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Affiliation(s)
- Ryo Miyajima
- Department of Chemistry, Faculty of Science, Niigata University, 8050 Ikarashi-2, Nishi-ku, Niigata 950-2181, Japan
| | - Yuuki Ooe
- Department of Chemistry, Faculty of Science, Niigata University, 8050 Ikarashi-2, Nishi-ku, Niigata 950-2181, Japan
| | - Tomoaki Miura
- Department of Chemistry, Faculty of Science, Niigata University, 8050 Ikarashi-2, Nishi-ku, Niigata 950-2181, Japan
| | - Tadaaki Ikoma
- Department of Chemistry, Faculty of Science, Niigata University, 8050 Ikarashi-2, Nishi-ku, Niigata 950-2181, Japan
| | - Hajime Iwamoto
- Department of Chemistry, Faculty of Science, Niigata University, 8050 Ikarashi-2, Nishi-ku, Niigata 950-2181, Japan
| | - Shin-Ya Takizawa
- Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | - Eietsu Hasegawa
- Department of Chemistry, Faculty of Science, Niigata University, 8050 Ikarashi-2, Nishi-ku, Niigata 950-2181, Japan
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Tay NES, Lehnherr D, Rovis T. Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis. Chem Rev 2022; 122:2487-2649. [PMID: 34751568 PMCID: PMC10021920 DOI: 10.1021/acs.chemrev.1c00384] [Citation(s) in RCA: 143] [Impact Index Per Article: 71.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Redox processes are at the heart of synthetic methods that rely on either electrochemistry or photoredox catalysis, but how do electrochemistry and photoredox catalysis compare? Both approaches provide access to high energy intermediates (e.g., radicals) that enable bond formations not constrained by the rules of ionic or 2 electron (e) mechanisms. Instead, they enable 1e mechanisms capable of bypassing electronic or steric limitations and protecting group requirements, thus enabling synthetic chemists to disconnect molecules in new and different ways. However, while providing access to similar intermediates, electrochemistry and photoredox catalysis differ in several physical chemistry principles. Understanding those differences can be key to designing new transformations and forging new bond disconnections. This review aims to highlight these differences and similarities between electrochemistry and photoredox catalysis by comparing their underlying physical chemistry principles and describing their impact on electrochemical and photochemical methods.
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Affiliation(s)
- Nicholas E. S. Tay
- Department of Chemistry, Columbia University, New York, New York, 10027, United States
| | - Dan Lehnherr
- Process Research and Development, Merck & Co., Inc., Rahway, New Jersey 07065, United States
| | - Tomislav Rovis
- Department of Chemistry, Columbia University, New York, New York, 10027, United States
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Light-triggered elimination of CO 2 and absorption of O 2 (artificial breathing reaction) in photolysis of 2-(4-nitrophenyl)-1H-indole derivatives. Photochem Photobiol Sci 2021; 20:421-434. [PMID: 33721275 DOI: 10.1007/s43630-021-00031-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Accepted: 02/18/2021] [Indexed: 01/09/2023]
Abstract
A new chromophore, 2-(4-nitrophenyl)-1H-indole (NPI), was synthesized as a potential photolabile protecting group. Caged benzoic acids featuring the NPI chromophore were synthesized as model compounds. Benzoic acid was released in moderate yields (~ 40-60%) upon photolysis of the caged benzoic acids without any additional chemical reagents. Interestingly, an aldehyde, 1-(5-(1-formyl-1H-indol-2-yl)-2-nitrophenyl)ethyl benzoate, was isolated in ≈ 20% together with benzoic acid (≈ 40%) in photolysis of a caged benzoic acid, 2-(2-(3-(1-(benzoyloxy)ethyl)-4-nitrophenyl)-1H-indol-1-yl)acetic acid. The functional group, CH2COOH, at the indole nitrogen was transformed into the aldehyde group, CHO, under photolysis conditions in air. The similar photochemical transformation was observed in the photolysis of 2-(2-(4-nitrophenyl)-1H-indol-1-yl)acetic acid, in which the benzoate group is not attached at the nitrophenyl ring. Products analysis, transient absorption spectroscopy, and computational study suggested that intramolecular electron transfer is key for the elimination of CO2 and absorption of O2 for the formation of the aldehyde. The artificial breathing-type reaction can apply to transition metal-free oxidation of amino acids under mild conditions.
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