Electrocatalytic C–N Coupling via Anodically Generated Hypervalent Iodine Intermediates

Maity, Asim; Frey, Brandon L.; Hoskinson, Nathaneal; Powers, David

doi:10.26434/chemrxiv.11472549

Cited by 1 publication

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“…The latter approach has provided a demonstration of the viability of hypervalent iodine electrosynthesis but fails to address the central challenge in catalysis, which is selective catalyst oxidation in the presence of oxidatively labile substrates. 55−57 Consistent with our hypothesis that carboxylate-stabilized iodanyl radicals are on-path for aerobic hypervalent iodine synthesis, our initial forays into aryl iodide electrocatalysis indicated a decisive role for carboxylate additives: 3 Electrolysis of biaryl amide 12, which was selected based on the seminal C−N bond-forming chemistry disclosed by Antonchick and co-workers, 58 in the presence of various aryl iodides and [TBA]PF 6 as a supporting electrolyte failed to deliver the desired carbazole product 13. The addition of one equivalent of [TBA]OAc as part of the supporting electrolyte mixture resulted in efficient C−N bond construction.…”

Section: Iodanyl Radical Electrochemistry and Electrocatalysismentioning

confidence: 55%

Iodanyl Radical Catalysis

2023

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Conspectus Hypervalent iodine reagents find application as selective chemical oxidants in a diverse array of oxidative transformations. The utility of these reagents is often ascribed to (1) the proclivity to engage being selective two-electron redox transformations; (2) facile ligand exchange at the three-centered, four-electron (3c–4e) hypervalent iodine–ligand (I–X) bonds; and (3) the hypernucleofugacity of aryl iodides. One-electron redox and iodine radical chemistry is well-precedented in the context of inorganic hypervalent iodine chemistryfor example, in the iodide–triiodide couple that drives dye-sensitized solar cells. In contrast, organic hypervalent iodine chemistry has historically been dominated by the two-electron I(I)/I(III) and I(III)/I(V) redox couples, which results from intrinsic instability of the intervening odd-electron species. Transient iodanyl radicals (i.e., formally I(II) species), generated by reductive activation of hypervalent I–X bonds, have recently gained attention as potential intermediates in hypervalent iodine chemistry. Importantly, these open-shell intermediates are typically generated by activation of stoichiometric hypervalent iodine reagents, and the role of the iodanyl radical in substrate functionalization and catalysis is largely unknown. Our group has been interested in advancing the chemistry of iodanyl radicals as intermediates in the sustainable synthesis of hypervalent I(III) and I(V) compounds and as novel platforms for substrate activation at open-shell main-group intermediates. In 2018, we disclosed the first example of aerobic hypervalent iodine catalysis by intercepting reactive intermediates in aldehyde autoxidation chemistry. While we initially hypothesized that the observed oxidation was accomplished by aerobically generated peracids via a two-electron I(I)-to-I(III) oxidation reaction, detailed mechanistic studies revealed the critical role of acetate-stabilized iodanyl radical intermediates. We subsequently leveraged these mechanistic insights to develop hypervalent iodine electrocatalysis. Our studies resulted in the identification of new catalyst design principles that give rise to highly efficient organoiodide electrocatalysts that operate at modest applied potentials. These advances addressed classical challenges in hypervalent iodine electrocatalysis related to the need for high applied potentials and high catalyst loadings. In some cases, we were able to isolate the anodically generated iodanyl radical intermediates, which allowed direct interrogation of the elementary chemical reactions characteristic of iodanyl radicals. Both substrate activation via bidirectional proton-coupled electron transfer (PCET) reactions at I(II) intermediates and disproportionation reactions of I(II) species to generate I(III) compounds have been experimentally validated. This Account discusses the emerging synthetic and catalytic chemistry of iodanyl radicals. Results from our group have demonstrated that these open-shell species can play a critical role in...

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Section: Iodanyl Radical Electrochemistry and Electrocatalysismentioning

confidence: 55%