A Challenge

Authors

DOI:

https://doi.org/10.29356/jmcs.v67i4.2077

Keywords:

electron transfer, electrolysis, sensitized photolyses

Abstract

The present contribution overviews several aspects of my groups’ involvement in the field of mediated electron transfer.  From the laboratories of its pioneers to the present day, the field maintains a position of interest and fundamental importance, and is now widely accepted and utilized.  I begin with a brief review of the basics where we will:

  • differentiate mediated and direct electrolysis;
  • highlight similarities between it and sensitized photolyses;
  • explore the steps/stages associated with a mediated process focusing particularly upon the kinetics and thermodynamics of the electron transfer step;
  • describe how to overcome the thermodynamic impasse that frequently accompanies electron transfer.

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Author Biography

R. Daniel Little, University of California, Santa Barbara

Department of Chemistry and Biochemistry

References

Little, R. D. People, Travel, Seminars, Reading, the Classroom, and Curiosity-Sources of Research Inspiration. J. Mex. Chem. Soc. 2010, 54(2), 122-132. DOI: https://doi.org/10.29356/jmcs.v54i2.956

(a) Francke, R.; Little, R.D. Redox catalysis in organic electrosynthesis: basic principles and recent developments, R. Chem. Soc. Rev. 2014, 43, 2492–2521. (b) Ogibin, Y. N.; Elinson, M. N.; Nikishin, G. I. Mediator oxidation systems in organic electrosynthesis, Russ. Chem. Rev. 2009, 78, 89–140. (c) Steckhan, E. Indirect Electroorganic Syntheses—A Modern Chapter of Organic Electrochemistry [New Synthetic Methods (59)], Angew. Chem. Int. Ed. Engl. 1986, 25, 683– 701.

Little, R. D. A Perspective on Organic Electrochemistry, J. Org. Chem. 2020, 85, 13375–13390. DOI: https://doi.org/10.1021/acs.joc.0c01408

Fox, D. P.; Little, R. D.; Baizer, M. M. Intramolecular Electroreductive Cyclization. J. Org. Chem. 1985, 50, 2202−2204. DOI: https://doi.org/10.1021/jo00212a043

Little, R. D., Moeller, K. D. Organic Electrochemistry as a Tool for Synthesis, Umpolong Reactions, Reactive Intermediates, and the Design of New Synthetic Methods, Electrochemical Society Interface, 2002, 11(4), 36-42. DOI: https://doi.org/10.1149/2.F06024IF

Fry, A. J.; Little, R. D.; Leonetti, J. A General Mechanistic Scheme for Intramolecular Electrochemical Hydrocyclizations. Mechanism of the Electroreductive Cyclization of ω-Keto-α,β-unsaturated Esters. J. Org. Chem. 1994, 59, 5017−5026. DOI: https://doi.org/10.1021/jo00096a054

Sowell, C. G.; Wolin, R. L.; Little, R. D. Electroreductive cyclization reactions. Stereoselection, creation of quaternary centers in bicyclic frameworks, and a formal total synthesis of quadrone. Tetrahedron Lett. 1990, 31, 485−488. DOI: https://doi.org/10.1016/0040-4039(90)87014-Q

Miranda, J. A.; Wade, C. J.; Little, R. D. Indirect Electroreductive Cyclization and Electrohydrocyclization Using Catalytic Reduced Nickel(II) Salen. J. Org. Chem. 2005, 70, 8017−8026. DOI: https://doi.org/10.1021/jo051148+

Wu, X.; Davis, A.P.; Lambert, P.; Kraig Steffen, L.; Toy, O.; Fry, A. J. Substituent effects on the redox properties and structure of substituted triphenylamines. An experimental and computational study, Tetrahedron, 2009, 65(12), 2408-2414. DOI: https://doi.org/10.1016/j.tet.2009.01.023

Park, Y.S.; Little, R.D. Redox Electron-Transfer Reactions: Electrochemically Mediated Rearrangement, Mechanism, and a Total Synthesis of Daucene, J. Org. Chem. 2008, 73, 6807– 6815. DOI: https://doi.org/10.1021/jo801199s

(a) Zhang, N.-t.; Zeng, C.-C.; Lam, C. M.; Gbur, R. K.; Little, R. D. Triarylimidazole Redox Catalysts: Electrochemical Analysis and Empirical Correlations, J. Org. Chem. 2013, 78, 2104–2110. (b) Zeng, C.-C.; Zhang, N.-t.; Lam, C. M.; Little, R. D. Novel Triarylimidazole Redox Catalysts: Synthesis, Electrochemical Properties, and Applicability to Electrooxidative C–H Activation, Org. Lett. 2012, 14, 1314– 1317.

Lu, N.-N.; Zhang, N.-T.; Zeng, C.-C.; Hu, L.-M.; Yoo, S. J.; Little, R. D. Electrochemically Induced Ring-Opening/Friedel−Crafts Arylation of Chalcone Epoxides Catalyzed by a Triarylimidazole Redox Mediator, J. Org. Chem. 2015, 80, 781−789. DOI: https://doi.org/10.1021/jo5022184

Francke, R.; Little, R.D. Optimizing Electron Transfer Mediators Based on Arylimidazoles by Ring Fusion: Synthesis, Electrochemistry, and Computational Analysis of 2-Aryl-1-methylphenanthro[9,10-d]imidazoles, J. Am. Chem. Soc. 2014, 136, 427– 435. DOI: https://doi.org/10.1021/ja410865z

Enders, P.; Májek, M. Lam, C. M.; Little, R.D.; Francke, R. How to Harness Electrochemical Mediators for Photocatalysis – A Systematic Approach Using the Phenanthro[9,10-d]imidazole Framework as a Test Case. ChemCatChem 2023, 15, e202200830, https://doi.org/10.1002/cctc.202200830

Rehm, D.; Weller, A. Kinetics of Fluorescence Quenching by Electron and H-Atom Transfer, Isr. J. Chem. 1970, 8, 259– 271. DOI: https://doi.org/10.1002/ijch.197000029

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Published

2023-10-02

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Section

Special Issue. Tribute to the electrochemical emeritus researchers of SNI
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