Beyond n-dopants for organic semiconductors: use of bibenzo[ d]imidazoles in UV-promoted dehalogenation reactions of organic halides

Kan Tang; Megan R Brown; Chad Risko; Melissa K Gish; Garry Rumbles; Phuc H Pham; Oana R Luca; Stephen Barlow; Seth R Marder

doi:10.3762/bjoc.19.142

Beyond n-dopants for organic semiconductors: use of bibenzo[ d]imidazoles in UV-promoted dehalogenation reactions of organic halides

Beilstein J Org Chem. 2023 Dec 14:19:1912-1922. doi: 10.3762/bjoc.19.142. eCollection 2023.

Authors

Kan Tang¹, Megan R Brown², Chad Risko², Melissa K Gish³, Garry Rumbles^{1

3

4}, Phuc H Pham⁵, Oana R Luca^{1

5}, Stephen Barlow^{1

3}, Seth R Marder^{1

3

4

5}

Affiliations

¹ Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80309, United States.
² Department of Chemistry & Center for Applied Energy Research (CAER), University of Kentucky, Lexington, Kentucky, 40506, United States.
³ National Renewable Energy Laboratory, Chemistry and Nanoscience Center, Golden, Colorado, 80401, United States.
⁴ Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80309, United States.
⁵ Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States.

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.

Keywords: dehalogenation; n-dopant; reduction; reductive dimerization.

Grants and funding

This work was authored in part by the National Renewable Energy Laboratory (NREL), operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. This work was primarily supported by the Laboratory Directed Research and Development (LDRD) Program at NREL. The DFT and TD-DFT calculations, performed at the University of Kentucky, were supported by the Center for Soft PhotoElectroChemical Systems (SPECS), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under award No. DE-SC0023411. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.