A case of chain propagation: α-aminoalkyl radicals as initiators for aryl radical chemistry

Abstract

The generation of aryl radicals from the corresponding halides by redox chemistry is generally considered a difficult task due to their highly negative reduction potentials. Here we demonstrate that -aminoalkyl...

Excitation of Radical Anions of Naphthalene Diimides in Consecutive‐ and Electro‐Photocatalysis**

“…Recently proposed halogen‐atom transfer (XAT) reactions of α‐aminoalkyl radicals could explain the slightly better performance of the conPET phototransformation, provided the radical derived from DIPEA could promote some extra formation of aryl radicals by bromide abstraction [54,55] . However, it is unlikely that a XAT process is responsible for all the product s formed because there is reaction in the absence of any amine (electroPET reaction).…”

“…[53] Recently proposed halogen-atom transfer (XAT) reactions of α-aminoalkyl radicals could explain the slightly better performance of the conPET phototransformation, provided the radical derived from DIPEA could promote some extra formation of aryl radicals by bromide abstraction. [54,55] However, it is unlikely that a XAT process is responsible for all the products formed because there is reaction in the absence of any amine (electro-PET reaction). This evidence, together with the recent direct observation of PET from PDI * À * to aryl halides (by picosecond time-resolved transient absorption (TA) spectroscopy), [27] give a strong support for the existence of a conPET process.…”

Non-Innocent Radical Ion Intermediates in Photoredox Catalysis: Parallel Reduction Modes Enable Coupling of Diverse Aryl Chlorides

“…These data fit within a growing body of literature that suggests terminal reductant byproducts can play a non-innocent role in photoredox catalysis. 65,66,75 We suspect that these results could also offer an alternative explanation for recent examples wherein isophthalonitrile catalysts have appeared to reduce substrates beyond their expected redox potentials 66,86 and, more broadly, illustrate the importance of radical ion intermediates in photoredox catalysis.…”

“…The isophthalonitrile catalysts, which are both excellent neutral chromophores 63 as well as electronprimed photoredox catalysts, 58 promoted the reaction most efficiently albeit still in poor yield. To exclude hydrogen atom transfer (XAT) aryl radical generation, [64][65][66] we examined the reductive defunctionalization of anilinium and aryl phosphate salts (Table 1). These are each challenging reductive cleavage reactions 67,68 of non-polarizable leaving groups unlikely to undergo XAT processes.…”

Photocatalytic Activity of Diverse Organic Radical Anions: Catalyst Discovery Enables Cleavage of Strong C(sp2)–N and C(sp2)–O Bonds

“…[57,58] We envisioned that cleavage of these strong bonds was a perfect arena to explore new potent reductants given recently reported halogen-atom transfer strategies, which in some cases can circumvent deeply reducing potentials, [59] are unlikely to be amenable to the cleavage of these less polarizable heteroatoms. [60,61] We initiated our studies with the reductive cleavage of an N,N,N-trimethyl anilinium salt, 1 (Table 1). We anticipated that the thermodynamic and kinetic challenges presented by aryl C(sp 2 )-N bond cleavage would expose the limitations of current electron-primed photocatalysts.…”