Abstract
Photoredox catalysis (PRC) and synthetic organic electrochemistry (SOE) are often considered competing technologies in organic synthesis. Their fusion has been largely overlooked. We review state‐of‐the‐art synthetic organic photoelectrochemistry, grouping examples into three categories: 1) electrochemically mediated photoredox catalysis (e‐PRC), 2) decoupled photoelectrochemistry (dPEC), and 3) interfacial photoelectrochemistry (iPEC). Such synergies prove beneficial not only for synthetic “greenness” and chemical selectivity, but also in the accumulation of energy for accessing super‐oxidizing or ‐reducing single electron transfer (SET) agents. Opportunities and challenges in this emerging and exciting field are discussed.
Highlights
Chemical synthesis by visible light is the fundamental process for biological photosynthesis on Earth
By mimicking the concept of nature, but stripping down the complexity of interlinked photosystems into defined single-molecule photocatalysts, researchers found that transition-metal complexes such as bipyridyl complexes of RuII and IrIII can harvest visible-light photons to become powerful excited-state single electron transfer (SET) agents for redox processes, and enjoy sufficiently long lifetimes (700–1100 ns)[2] to undergo diffusion-controlled redox events
Seminal papers demonstrated the synthetic applications of RuII and IrIII bipyridyl complexes.[5,6,7]
Summary
Chemical synthesis by visible light is the fundamental process for biological photosynthesis on Earth. With sustainability and cost at the forefront of minds in academia and chemical industry,[8] researchers were quick to challenge the presence of rare mid-row transition metals with examples of organophotocatalysts such as eosin Y, Rose Bengal, and acridinium salts, as noted in seminal papers and reviews.[4d–g,9–11] Recently, the use of more sustainable transition-metal-based coordination compounds such as those of iron, nickel, and copper, whose excited-state lifetimes are much shorter (rendering their application more challenging), are starting to receive attention.[12] PRC is attractive for a variety of reasons reviewed elsewhere,[4,13] but arguably the biggest advantage is that use of visible light precludes direct excitation of substrates (leading to difficult-to-control highenergy pathways and decomposition), selectively transferring energy to the photocatalyst chromophore Another vehicle for SET chemistry, which has been undergoing a renaissance in recent years, is synthetic organic electrochemistry (SOE). SOE is advantageous for several reasons that are well-documented,[21] but arguably the biggest advantage of SOE is the ability to dial in any potential, and the redox window is in theory only limited by the tolerance of the reaction solvent
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