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

Abstract

Synthetic photoelectrochemistry (PEC) is receiving increasing attention as a new frontier for the generation and handling of reactive intermediates. PEC permits selective single‐electron transfer (SET) reactions in a much greener way and broadens the redox window of possible transformations. Herein, the most recent contributions are reviewed, demonstrating exciting new opportunities, namely, the combination of PEC with other reactivity paradigms (hydrogen‐atom transfer, radical polar crossover, energy transfer sensitization), scalability up to multigram scale, novel selectivities in SET super‐oxidations/reductions and the importance of precomplexation to temporally enable excited radical ion catalysis.

Radical Hydrodifluoromethylation of Unsaturated C-C Bonds via an Electroreductively Triggered Two-pronged Approach

“…To invent a less oxidizing hydrodifluoromethylation system, we anticipated an electroreductive reaction conditions using a sacrificial anode (Fig 2). [50][51][52][53][54][55][56][57][58][59][60][61][62][63] A cathodic reduction of A would furnish a CF2H radical (B), which would afford carbon-centered radical D upon addition into alkene substrate. Two mechanistic scenarios are envisioned based upon electronic properties of the employed alkenes.…”

Ritter-type amination of C(sp3)-H bonds enabled by electrochemistry with SO42−

“…However, C-H amination through HAT process enabled by electrochemistry and electrophotocatalysis 51 – 54 could enlarge the substrate scope to unactivated alkanes. For instance, the remote inert C(sp 3 )-H bonds amination was developed to construct pyrrolidines through 1,5-HAT process, which was initiated by the electrochemical generated N radical 55 – 57 .…”

Solvated Electrons! The Missing Link in Highly Reducing Photocatalysis

“…1,5 In recent years, several elegant reports have shown that open-shell doublet organic radicals, generated in-situ, either electrochemically 6,7 or photochemically via a consecutive two-photon excitation process, 8 can act as potent photoreducing agents. 9 In both processes, the open-shell doublet organic radical PC • (anionic or neutral) is generated in-situ from a closed-shell singlet species (neutral or cationic), followed by photoexcitation generating the radical excited state PC • * that can act as a super photoreducing agent (E1/2 red * = -2.3 to -3.4 V vs SCE). 10 The concept of a two-photon excitation process, commonly purported as a consecutive photoelectron transfer (conPET) pathway, has been reported with numerous notable photocatalysts such as PDI, DCA, anthraquinone, Rhodamine 6G, benzo[ghi]perylene (BPI), 4-DPAIPN, 3-CzEPAIPN, Mes-Acr, and Deazaflavin.…”