Proton‐Coupled Electron Transfer (PCET) with 1,4‐Bisguanidino‐Benzene Derivatives: Comparative Study and Use in Acid‐Initiated C‐H Activation
| Autor: | Petra Walter, Olaf Hübner, Elisabeth Kaifer, Hans-Jörg Himmel |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
proton-coupled electron transfer
proton affinity Hot Paper Electrons Protonation Redox C−H activation Catalysis redox potential Electron Transport Electron transfer chemistry.chemical_compound Computational chemistry Benzene Derivatives Reactivity (chemistry) Full Paper Organic Chemistry Chloranil General Chemistry Full Papers chemistry Intramolecular force Proton affinity Protons Proton-coupled electron transfer Oxidation-Reduction guanidines |
| Zdroj: | Chemistry (Weinheim an Der Bergstrasse, Germany) |
| ISSN: | 1521-3765 0947-6539 |
| DOI: | 10.1002/chem.202101539 |
| Popis: | Proton‐coupled electron transfer (PCET) is of key importance in modern synthetic chemistry. Redox‐active guanidines were established by our group as valuable alternatives to toxic high‐potential benzoquinones in a variety of different PCET reactions. In this work, the PCET reactivity of a series of 1,4‐bisguanidino‐benzenes varying in their redox potentials and proton affinities is evaluated. The relevant redox and protonation states are fully characterized, and the compounds sorted with respect to their PCET reactivity by comparative PCET experiments supplemented by quantum‐chemical calculations. Depending on the studied reactions, the driving force is either electron transfer or proton transfer; thereby the influence of both processes on the overall reactivity could be assessed. Then, two of the PCET reagents are applied in representative oxidative aryl‐aryl coupling reactions, namely the intramolecular coupling of 3,3’’‐4,4’’‐tetramethoxy‐o‐terphenyl to give the corresponding triphenylene, the intermolecular coupling of N‐ethylcarbazole to give N,N’‐diethyl‐3,3’‐bicarbazole, and in the oxidative lactonization of 2‐[(4‐methoxyphenyl)methyl]‐benzoic acid. Under mild conditions, the reactions proceed fast and efficient. Only small amounts of acid are needed, in clear contrast to the corresponding coupling reactions with traditional high‐potential benzoquinones such as DDQ or chloranil requiring a large excess of a strong acid. 1,4‐Bisguanidino‐benzenes are versatile reagents in proton‐coupled electron transfer (PCET) reactions. In this work the effect of guanidino group modification on the PCET reactivity is evaluated (X=H or OMe) and the best performing two compounds applied in intra‐ and inter‐molecular aryl‐aryl coupling and oxidative lactonization test reactions. In difference to related reactions with high‐potential benzoquinones, only a small amount of acid is required to inititiate efficient reactions under mild conditions. |
| Databáze: | OpenAIRE |
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