Hole-mediated photoredox catalysis: tris(p-substituted)biarylaminium radical cations as tunable, precomplexing and potent photooxidants

Abstract

Triarylamines are demonstrated as novel, tunable electroactivated photocatalysts that use dispersion precomplexation to harness the full potential of the visible photon (>4.0 V vs. SCE) in anti-Kasha photo(electro)chemical super-oxidations of arenes.

Recent advances in visible light-activated radical coupling reactions triggered by (i) ruthenium, (ii) iridium and (iii) organic photoredox agents

“…The examples shown in Scheme 245 feature C-H substitution by azoles. 277 The formation of fluoroarene 904m from fluorobenzene shows that this is a highly powerful oxidising system for arenes and competitive with those discussed above [from the teams of Nicewicz and Lambert]. The best catalyst used in this transformation, TCBPA, was calculated to be a very strong oxidant (E red * = +4.19 V vs. SCE).…”

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

“…An electrochemically generated radical ion implies replacing a stoichiometric amount of a sacrificial donor by a cathode, a situation that could be very advantageous having an easily tunable source of electrons. This was recognized by Lambert's and Wickens’ groups, among others who recently developed synthetic transformation s using radical anions and radical cations [16,17,33–35] …”

“…This was recognized by Lambert's and Wickens' groups, among others who recently developed synthetic transformations using radical anions and radical cations. [16,17,[33][34][35] In particular, Lambert and Lin et al [16] used dicyanoanthracene (DCA) as the catalyst to modify aryl chlorides performing borylation and CÀ H functionalization (Scheme 4). A photo-EC' mechanism was proposed for the formation of aryl radicals involving a key PET from the excited DCA * À to aryl halides, without detailed studies.…”

Electro-mediated PhotoRedox Catalysis for Selective C(sp3)-O Cleavages of Phosphinates to Carbanions

“…6 Despite these elegant advances, reductive e-PRC and biphotonic strategies 3 are still heavily focused on the reductions of aryl halides/pseudohalides through C(sp 2 )-X bond cleavages to generate aryl C(sp 2 ) radicals in an overall dehalogenation or functionalization with excesses of radical trapping agents. 5f,h Inspired by previous reports, 5 we envisioned that phosphinates of aliphatic alcohols (E p red = -2.2  -2.6 V vs. SCE) could undergo e-PRC reduction to give carbanions (Figure 1B). Thereby, an electroactivated-PhotoRedox Catalyst (e-PRCat) undergoes cathodic activation and photoexcitation to afford a potent reductant.…”

“…4 Merging the advantages of these two important techniques has made photoelectrochemistry a tool for greener, more challenging and more selective molecular activations. 5 Pioneering reports by Xu, 5b-c,o Lambert, 5g,h,i,k Lin 5h,j and Wickens 5f have shown that introducing applied potential in photoredox catalysis is not only beneficial for accessing challenging redox reactions, but is also a green replacement for sacrificial redox additives. Among the various strategies for combining photocatalysis and electrochemistry 4a the sub-category coined electrochemically-mediated PhotoRedox Catalysis (e-PRC) is highly attractive.…”