The role of photocatalysts in radical chains in homolytic aromatic substitution, radical addition to olefins, and nucleophilic radical substitution mechanisms

Abstract

<p>Initiation, propagation and chain termination steps in oxidative and reductive quenching cycles for the photoinitiated perfluoroalkylation reaction of an olefin.</p>

Visible light-catalyzed fluoroalkylation reactions of free aniline derivatives

“…The lowest radical chain is that for PC-3 (i.e., zinc phthalocyanine), where path D, Scheme 13, seemed not to play a relevant role when PC-3 is employed. Experimental evidence supports these observations when comparing photoreaction times (PC-3 needs prolonged reaction times, as compared to PC-1 and -2) [40].…”

“…The photoactive photocatalyst RB is re-generated from its radical cation by reduction with carbonate anion, yielding carbonate radical anion and thermoneutral RB. In another study [40], we postulated an alternative regeneration of the photoactive catalyst Rose Bengal which is Replacing the inorganic base Cs 2 CO 3 for N,N,N′,N′tetramethylethylenediamine (TMEDA), we uncovered that in the presence of molecular iodine and absence of organic dye Rose Bengal as photocatalyst, the complex formed between TMEDA and I 2 (i.e., [(TMEDA)I.I 3 ]) was capable of producing R F radicals when irradiation took place with a compact fluorescent lamp (CFL) [41]. Thus, the visible light-activated complex [(N,N,N`,N`-tetramethylethylenediamine) I.I 3 ] (i.e., [(TMEDA)I.I 3 ]) in the presence of perfluoroalkyl iodides, R F -I produced R F radicals efficiently, making possible substitution reactions on amino-aromatics.…”

“…This process has a favorable Gibbs energy (ΔG ET = − 0.775 V) The anion radical of the photocatalyst should reduce R F -I to R F radicals, which in turn substitute the aniline derivative. Further comparative mechanistic studies on perfluoroalkylation of anilines derivatives under red-light photocatalysis was carried out by Yerien and colleagues, where radical a.-para : ortho raƟo Scheme 11 Selected examples for the perfluorobutylation of aniline derivatives under red-light photocatalysis chain lengths were compared between different photocatalysts [40].…”

“…In a parallel study [40] the efficiency of different photocatalysts (Rose Bengal, (Ir[(dF(CF 3 )ppy] 2 (dtbbpy) + , and zinc phthalocyanine) on the perfluorobutylation of 4-methylaniline was compared, employing different light sources (green LEDs, violet LEDs, and red LEDs, respectively). The perfluorobutylation of 4-methylaniline under Rose Bengal photocatalysis is made possible through an oxidative quenching cycle of the photocatalyst, whereas the same reaction under Ir[(dF(CF 3 )ppy] 2 (dtbbpy) + , or zinc phthalocyanine photocatalysts are conducted under reductive quenching cycles of the photocatalysts.…”

Rose Bengal-photocatalyzed perfluorohexylation reactions of organic substrates in water. Applications to late-stage syntheses

“…In the realm of visible light photocatalysis, fluoroalkylation reactions play a considerable part, as generation of fluoroalkyl radicals R F • by this method is well documented [7][8][9]. Our group has contributed to this subject with several examples [10][11][12][13][14] on visible light-photocatalyzed fluoroalkylation strategies in organic solvents.…”