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

Abstract

Both photo-and electrochemical transformations represent excellent opportunities for the development of environmentally friendly methodologies which, if combined, would result in improved methodologies. Thus, we present here a family of naphthalene diimide photocatalysts comparing a "pure" photochemical and an electro-photochemical transformation; by means of a CÀ H substitution in (hetero)aromatic systems with CÀ C bond formation. We identify a system that has the potential to be applied in both approaches with minor changes in the reaction conditions and recognize the excitation of radical anion of naphthalene diimides as the key event. Both approaches produce similar yields and reaction rates, although a consecutive photoinduced electron transfer (conPET) process shows in principle a simpler setup and more tolerance to a poor catalyst solubility, the electro-PET process improves selectivity and gives more room for optimization. The more accessible "pure" photochemical approach could be used as an initial assessment for photocatalytic transformation and electrophotocatalytic transformation.

Electrochemical Activation of Diverse Conventional Photoredox Catalysts Induces Potent Photoreductant Activity**

“…We next questioned whether the aryl radical intermediates generated upon reductive cleavage of anlinium salts and phosphate esters could be intercepted by classic aryl radical traps.W einvestigated several aryl radical coupling reactions: phosphonylation, borylation, and heteroarylation (27)(28)(29). We found that both C(sp 2 ) À Na nd C(sp 2 ) À Or adical precursors were amenable to each of these radical coupling reactions (Figure 4).…”

“…[12,13] Indeed, in the context of reductions,alkali metals have remained reductants of unparalleled potencyf or over ac entury.T hese reagents continue to be used in both academic [14,15] and industrial [16] settings despite their implicit hazards,poor chemoselectivity, and inextricable chemical waste.T oaddress this,the development of new strategies to deliver extreme reduction potentials (significantly more negative than À2V vs.S CE) with the safety and chemoselectivity profile of photoredox catalysis is an emerging area of considerable contemporary interest. [11,[17][18][19][20][21][22] Over the past several years,n umerous groups, [23][24][25][26][27][28] including ours, [26] have examined catalytic systems designed to leverage mildly reducing radical species as anew family of photocatalysts (Figure 1, top). We have dubbed these reductively activated species electron-primed photoredox catalysts to distinguish them from more conventional photocatalytic reductants.P ioneering work from Kçnig used ac onsecutive photoinduced electron transfer (conPET) approach to photochemically generate an electron-primed photocatalyst, albeit one that did not possess an excited state reduction potential more negative than À2V vs.S CE.…”

Synthetic Molecular Photoelectrochemistry: New Frontiers in Synthetic Applications, Mechanistic Insights and Scalability

“…When the debromination of 4‐bromobiphenyl ( E p red ≈−2.43 V vs. SCE) [46] was used to optimize reaction conditions, a bis‐ N ‐(2,2′,6,6′‐diisopropyl)naphthalene diimide ( NDI‐d ) precatalyst afforded dehalogenated product 21 a in a lower yield than NpMI did (Figure 13 A). Bardagi and co‐workers recently reported conPET and e‐PRC reductions of 4‐bromobenzonitrile ( E p red =−1.95 V vs. SCE) using a modified naphthalene diimide precatalyst ( NDI‐c ) [19m] . The aryl(sp 2 ) radical was trapped by an excess of benzene and afforded desired products (such as 21 b ) albeit in low yields (<20 %) (Figure 13 B).…”

Synthetische molekulare Photoelektrochemie: neue synthetische Anwendungen, mechanistische Einblicke und Möglichkeiten zur Skalierung

“…Die Debromierung von 4‐Brombiphenyl ( E p red ≈−2,43 V vs. SCE) [46] mit Bis‐ N ‐(2,2′,6,6′‐diisopropyl)naphthaldiimid ( NDI‐d ) zu 21 a lieferte geringere Ausbeuten als durch NpMI (Abbildung 13 A). Bardagi berichtete daraufhin über conPET‐ und e‐PRC‐Reduktionen von 4‐Brombenzonitril ( E p red =−1,95 V vs. SCE) unter Verwendung eines modifizierten Naphthaldiimids ( NDI‐c ) [19m] . Das generierte Aryl(sp 2 )‐Radikal wurde hierbei durch einen Überschuss an Benzol abgefangen ( 21 b ), wenn auch in geringer Ausbeute (<20 %, Abbildung 13 B).…”