Tailored Coumarin Dyes for Photoredox Catalysis: Calculation, Synthesis, and Electronic Properties

Abstract

High level time‐dependent density functional theory (TD‐DFT) computational modeling of coumarin dyes has been exploited for guiding the design of effective photocatalysts (PCs). A library of coumarins were investigated from the theoretical point of view and photophysical/electrochemical properties (absorption and emission spectra, E00, oxidation and reduction potentials) were evaluated. Comparison with literature values reported for a few candidates has been used for assessing the level of theory. On the basis of the results obtained, new strongly reducing PCs [Eox(PC.+/PC*)=−2.1 – −2.0 V vs SCE] were discovered. Through the computational study of structure‐properties relationships, a number of coumarins derivatives have been synthesized and evaluated in the pinacol coupling of aldehydes as the model reaction. The new organic photoredox catalysts show experimental photophysical and electrochemical data in accordance with the ones predicted by calculation, with excited state reduction potentials surpassing those of highly reducing transition metal‐based PCs. A careful investigation of their behavior as PC has revealed crucial issues that need to be taken into consideration in the general photoredox catalysis, shedding light on the use of these PC in the pinacol, as well as, in other photoredox reactions.

Chemodivergent Photocatalytic Synthesis of Dihydrofurans and β,γ‐Unsaturated Ketones

“…[i] For the structure of employed coumarin see ref. [45]. rt = room temperature, bpy = 2,2'-bipyridine, ppy = 2-phenylpyridinato, dtbbpy = 4,4'-di-tert-butyl-2,2'-dipyridyl, DPA = diphenylamine, 2FBN = 3,5-difluoro benzonitrile, DMF = N,N-dimethylformamide, nd = not determined.…”

“…Some organic photocatalysts were also tested. Eosin Y [E* ox (cat * + /cat*) = À 1.15 V vs SCE] [43] (entry 14), 3DPA2FBN [E* ox (cat * + /cat*) = À 1.60 V vs SCE] [44] (entry 15), and a highly reducing coumarin recently proposed by Cozzi et al [E* ox (cat * + /cat*) = À 1.89 V vs SCE] [45] (entry 16) were not able to promote the dihydrofuran formation. Our optimization study continued by investigating the reaction time (see Supporting Information) and 24 hours was identified as the best one.…”

[2.2]Paracyclophane-based coumarins: effective organo-photocatalysts for light-induced desulfonylation processes

“…Coumarin dyes are known to be able to mimic powerful reductant [Ir( iii )] complexes in various light-promoted transformations, such as the radical coupling of carbonyl compounds and imines, the trifluoromethylation of alkenes or the reductive protonation of bromoketones. 17…”

Generation and reaction of alanyl radicals in open flasks

“…As depicted in Fig. 1, the action of HE 15 and diazonium salt 16 in an open reaction vessel, allowed the in situ generation and Giese-type reaction of dipeptides and tripeptides containing a latent alanyl radical unit, regardless of whether it was at the C-terminus (28 and 34), N-terminus (25-27, and 29-33), or in the middle (35)(36)(37). The range of activated alkenes that were compatible with the process included simple a,b-unsaturated aromatic enones (25, 26, 31, and 36), heteroaromatic enones (28-30, 34 and 35), a phosphine oxide (27), a sulphone (36), an ynone (32), and an alkyl enone (37).…”

“…Indeed, light absorption enables them to function as discrete photocatalyts in their own right, and coumarins are a recent class of organic photoredox catalysts used for effecting a range of transformations. 35,36 To illustrate the advantages of the current method, a comparison of photoredox-catalyzed and the open flask methods are shown in Scheme 5.…”