Integrating Organic Lewis Acid and Redox Catalysis: The Phenalenyl Cation in Dual Role

Abstract

In recent years, merging different types of catalysis in a single pot has drawn considerable attention and these catalytic processes have mainly relied upon metals. However, development of a completely metal free approach integrating organic redox and organic Lewis acidic property into a single system has been missing in the current literature. This study establishes that a redox active phenalenyl cation can activate one of the substrates by single electron transfer process while the same can activate the other substrate by a donor-acceptor type interaction using its Lewis acidity. This approach has successfully achieved light and metal-free catalytic C-H functionalization of unactivated arenes at ambient temperature (39 entries, including core moiety of a top-selling molecule boscalid), an economically attractive alternative to the rare metal-based multicatalysts process. A tandem approach involving trapping of reaction intermediates, spectroscopy along with density functional theory calculations unravels the dual role of phenalenyl cation.

Storing redox equivalent in the phenalenyl backbone towards catalytic multi-electron reduction

“…We have previously observed that the redox active PLY can facilitate single electron transfer (SET) to a class of substrates 42–44. In recent reports, we established that the reduced phenalenyl radical triggers a SET process to execute transition metal-free C–H functionalization 42,44. Since redox equivalents can be stored in 2 , we envisaged that similar SET could be augmented to accomplish reduction of carboxylic acids by silane.…”

“…This fact is fully consistent with a redox active PLY-ligand where the highly conjugated ligand backbone harbors the redox equivalent. We have previously observed that the redox active PLY can facilitate single electron transfer (SET) to a class of substrates 42–44. In recent reports, we established that the reduced phenalenyl radical triggers a SET process to execute transition metal-free C–H functionalization 42,44.…”

An Iron‐Based Long‐Lived Catalyst for Direct C−H Arylation of Arenes and Heteroarenes

“…It may be noted that the same NBMO of phenalenyl based molecules earlier played a key role in designing molecules with several intriguing properties such as organic magnets, conductors, organic spin based electronics, and batteries . Only recently, the use of phenalenyl‐based molecules has been evolving for the design of various catalysts . The topic of phenalenyl‐based molecules to design various catalysts and spin electronic materials was reviewed recently …”

“…[25][26][27][28][29][30][31][32][33][34] Only recently,t he use of phenalenyl-based molecules has been evolving for the design of variousc atalysts. [35][36][37] The topico fp henalenyl-based moleculest od esign variousc atalysts ands pin electronic materials was reviewed recently. [38] We initiatedt he present study by optimizing the reaction conditions for direct CÀHa rylation of thiophene( 2a)w ith para-chlorophenyl diazo-tetrafluoroborate salt (3a)u sing Fe(PLY-O,O) 3 (1)c atalyst (see the Supporting Information, Ta ble S1).…”

Switching between mono and doubly reduced odd alternant hydrocarbon: designing a redox catalyst

“…20 Recently, such in situ generated mono-reduced phenalenyl based radicals were reported in designing cathode materials for single component H 2 O 2 fuel cell 21 and in electron transfer catalysis during various organic transformations. [22][23][24][25] Such approach using in-situ generated mono-reduced phenalenyl radicals opens a possibility to bridge between two seemingly dissimilar areas such as spin-electronics and catalysis. 26…”