Organic Photoredox Catalysis

Abstract

In this review, we highlight the use of organic photoredox catalysts in a myriad of synthetic transformations with a range of applications. This overview is arranged by catalyst class where the photophysics and electrochemical characteristics of each is discussed to underscore the differences and advantages to each type of single electron redox agent. We highlight both net reductive and oxidative as well as redox neutral transformations that can be accomplished using purely organic photoredox-active catalysts. An overview of the basic photophysics and electron transfer theory is presented in order to provide a comprehensive guide for employing this class of catalysts in photoredox manifolds.

Anthraquinones as Photoredox Catalysts for the Reductive Activation of Aryl Halides

“…[1][2][3][4][5][6][7][8][9] Ru-and Ir-based coordination complexes have received enormous attention because of their excellent visible-light-harvesting properties, modest to extremely high oxidation and reduction potentials, relatively long excited-state lifetimes, and reasonably good chemical and photostabilities under synthetic oxidative and reductive conditions. [2] In addition, considerable efforts have been made to develop metal-free photoredox catalytic methods with organic dyes [8,[10][11][12][13][14] such as eosin Y [10,11] or rhodamine derivatives [13,14] and organic heterogeneous photocatalysts [15] for synthetic transformations.…”

“…Quinones [8,16,17] occur in nature and are known for their excellent electron-accepting and hydrogen-abstracting abilities. [16,18] Not surprisingly, different quinone derivatives have been used for photo-oxidative transformations under visible light.…”

Photoredox Imino Functionalizations of Olefins

“…To accomplish this goal, we selected the methyl acridinium perchlorate 4 ( E* 1/2 =+2.06 V vs. SCE)3c, 17 as the photoredox catalyst and evaluated a range of solvents and bases under blue LED irradiation. Pleasingly, in the presence of an aryl‐disulfide as H‐atom relay catalyst,18 and 2,6‐lutidine as the base, 5 a was obtained in 81 % yield, which, to the best of our knowledge, represents the first fully catalytic radical hydroimination of olefins.…”

Photoorganocatalytic α-oxyamination of aldehydes

“…14,15 Recently, however, it was shown that in certain cases, simple and inexpensive organic dyes could be used as photoredox catalysts, thus making the processes greener and more suitable for large scale pharmaceutical production. 16 For example, Zeitler et al performed organocatalytic α-alkylation of aldehydes in the presence of eosin Y, which originally exploited Ru(bpy) 3 Cl 2, 17 giving the desired products with similar yields and enantiomeric excesses. 18 Hence, we envisaged that the visible-light driven oxyamination reaction described could be realized with organic dyes eliminating the need for the use of precious metal complexes.…”