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Tang K, Brown MR, Risko C, Gish MK, Rumbles G, Pham PH, Luca OR, Barlow S, Marder SR. Beyond n-dopants for organic semiconductors: use of bibenzo[ d]imidazoles in UV-promoted dehalogenation reactions of organic halides. Beilstein J Org Chem 2023; 19:1912-1922. [PMID: 38116245 PMCID: PMC10729154 DOI: 10.3762/bjoc.19.142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2023] [Accepted: 11/28/2023] [Indexed: 12/21/2023] Open
Abstract
2,2'-Bis(4-dimethylaminophenyl)- and 2,2'-dicyclohexyl-1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d]imidazole ((N-DMBI)2 and (Cyc-DMBI)2) are quite strong reductants with effective potentials of ca. -2 V vs ferrocenium/ferrocene, yet are relatively stable to air due to the coupling of redox and bond-breaking processes. Here, we examine their use in accomplishing electron transfer-induced bond-cleavage reactions, specifically dehalogenations. The dimers reduce halides that have reduction potentials less cathodic than ca. -2 V vs ferrocenium/ferrocene, especially under UV photoexcitation (using a 365 nm LED). In the case of benzyl halides, the products are bibenzyl derivatives, whereas aryl halides are reduced to the corresponding arenes. The potentials of the halides that can be reduced in this way, quantum-chemical calculations, and steady-state and transient absorption spectroscopy suggest that UV irradiation accelerates the reactions via cleavage of the dimers to the corresponding radical monomers.
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Affiliation(s)
- Kan Tang
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Megan R Brown
- Department of Chemistry & Center for Applied Energy Research (CAER), University of Kentucky, Lexington, Kentucky, 40506, United States
| | - Chad Risko
- Department of Chemistry & Center for Applied Energy Research (CAER), University of Kentucky, Lexington, Kentucky, 40506, United States
| | - Melissa K Gish
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States
| | - Garry Rumbles
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States,
| | - Phuc H Pham
- Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Oana R Luca
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
- Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Stephen Barlow
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States
| | - Seth R Marder
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States
- National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States,
- Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States
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Jiang Y, Yorimitsu H. Taming Highly Unstable Radical Anions and 1,4-Organodilithiums by Flow Microreactors: Controlled Reductive Dimerization of Styrenes. JACS Au 2022; 2:2514-2521. [PMID: 36465543 PMCID: PMC9709950 DOI: 10.1021/jacsau.2c00375] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Revised: 10/05/2022] [Accepted: 10/05/2022] [Indexed: 05/21/2023]
Abstract
The reduction of styrenes with lithium arenide in a flow microreactor leads to the instantaneous generation of highly unstable radical anions that subsequently dimerize to yield the corresponding 1,4-organodilithiums. A flow reactor with fast mixing is essential for this reductive dimerization as the efficiency and selectivity are low under batch conditions. A series of styrenes undergo dimerization, and the resulting 1,4-organodilithiums are trapped with various electrophiles. Trapping with divalent electrophiles affords precursors for useful yet less accessible cyclic structures, for example, siloles from dichlorosilanes. Thus, we highlight the power of single-electron reduction of unsaturated compounds in flow microreactors for organic synthesis.
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