Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis

Chemical Reviews, Journal Year: 2021, Volume and Issue: 122(2), P. 2487 - 2649

Published: Nov. 9, 2021

Redox processes are at the heart of synthetic methods that rely on either electrochemistry or photoredox catalysis, but how do and catalysis compare? Both approaches provide access to high energy intermediates (e.g., radicals) enable bond formations not constrained by rules ionic 2 electron (e) mechanisms. Instead, they 1e mechanisms capable bypassing electronic steric limitations protecting group requirements, thus enabling chemists disconnect molecules in new different ways. However, while providing similar intermediates, differ several physical chemistry principles. Understanding those differences can be key designing transformations forging disconnections. This review aims highlight these similarities between comparing their underlying principles describing impact electrochemical photochemical methods.

Language: Английский

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Luminescent First-Row Transition Metal Complexes

JACS Au, Journal Year: 2021, Volume and Issue: 1(11), P. 1860 - 1876

Published: Sept. 24, 2021

Precious and rare elements have traditionally dominated inorganic photophysics photochemistry, but now we are witnessing a paradigm shift toward cheaper more abundant metals. Even though emissive complexes based on selected first-row transition metals long been known, recent conceptual breakthroughs revealed that much broader range of in different oxidation states useable for this purpose. Coordination compounds V, Cr, Mn, Fe, Co, Ni, Cu show electronically excited with unexpected reactivity photoluminescence behavior. Aside from providing compact survey the key advances dynamic field, our Perspective identifies main design strategies enabled discovery fundamentally new types 3d-metal-based luminophores photosensitizers operating solution at room temperature.

Language: Английский

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Non-innocent Radical Ion Intermediates in Photoredox Catalysis: Parallel Reduction Modes Enable Coupling of Diverse Aryl Chlorides

Journal of the American Chemical Society, Journal Year: 2021, Volume and Issue: 143(29), P. 10882 - 10889

Published: July 13, 2021

We describe a photocatalytic system that elicits potent photoreductant activity from conventional photocatalysts by leveraging radical anion intermediates generated in situ. The combination of an isophthalonitrile photocatalyst and sodium formate promotes diverse aryl coupling reactions abundant but difficult to reduce chloride substrates. Mechanistic studies reveal two parallel pathways for substrate reduction both enabled key terminal reductant byproduct, carbon dioxide anion.

Language: Английский

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Unveiling Extreme Photoreduction Potentials of Donor–Acceptor Cyanoarenes to Access Aryl Radicals from Aryl Chlorides

Journal of the American Chemical Society, Journal Year: 2021, Volume and Issue: 143(33), P. 13266 - 13273

Published: Aug. 16, 2021

Since the seminal work of Zhang in 2016, donor–acceptor cyanoarene-based fluorophores, such as 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), have been widely applied photoredox catalysis and used excellent metal-free alternatives to noble metal Ir- Ru-based photocatalysts. However, all reported reactions involving this chromophore family are based on harnessing energy from a single visible light photon, with limited range redox potentials −1.92 +1.79 V vs SCE. Here, we document unprecedented discovery that fluorophores can undergo consecutive photoinduced electron transfer (ConPET) achieve very high reduction potentials. One newly synthesized catalysts, 2,4,5-tri(9H-carbazol-9-yl)-6-(ethyl(phenyl)amino)isophthalonitrile (3CzEPAIPN), possesses long-lived (12.95 ns) excited radical anion form, 3CzEPAIPN•–*, which be activate reductively recalcitrant aryl chlorides (Ered ≈ −1.9 −2.9 SCE) under mild conditions. The resultant radicals engaged synthetically valuable aromatic C–B, C–P, C–C bond formation furnish arylboronates, arylphosphonium salts, arylphosphonates, spirocyclic cyclohexadienes.

Language: Английский

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Metal-free reduction of CO2 to formate using a photochemical organohydride-catalyst recycling strategy

Nature Chemistry, Journal Year: 2023, Volume and Issue: 15(6), P. 794 - 802

Published: March 23, 2023

Language: Английский

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Photoredox-active Cr(0) luminophores featuring photophysical properties competitive with Ru(II) and Os(II) complexes

Nature Chemistry, Journal Year: 2023, Volume and Issue: 15(12), P. 1730 - 1736

Published: Aug. 14, 2023

Coordination complexes of precious metals with the d6 valence electron configuration such as Ru(II), Os(II) and Ir(III) are used for lighting applications, solar energy conversion photocatalysis. Until now, made from abundant first-row transition competitive photophysical photochemical properties have been elusive. While previous research efforts focused mostly on Fe(II), we disclose that isoelectronic Cr(0) gives access to higher photoluminescence quantum yields excited-state lifetimes when compared any other metal complex reported so far. The luminescence behaviour metal-to-ligand charge transfer excited states these is polypyridines. With complexes, become exploitable in photoredox catalysis, benchmark chemical reductions proceed efficiently under low-energy red illumination. Here demonstrate appropriate molecular design strategies open up new perspectives photophysics photochemistry metals.

Language: Английский

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

Angewandte Chemie International Edition, Journal Year: 2021, Volume and Issue: 60(39), P. 21418 - 21425

Published: July 20, 2021

Herein, we disclose that electrochemical stimulation induces new photocatalytic activity from a range of structurally diverse conventional photocatalysts. These studies uncover electron-primed photoredox catalyst capable promoting the reductive cleavage strong C(sp2 )-N and )-O bonds. We illustrate several examples synthetic utility these deeply reducing but otherwise safe mild catalytic conditions. Finally, employ current measurements to perform reaction progress kinetic analysis. This technique reveals improved this system is consequence an enhanced stability profile.

Language: Английский

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Cobalt(III) Carbene Complex with an Electronic Excited-State Structure Similar to Cyclometalated Iridium(III) Compounds

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 144(22), P. 9859 - 9873

Published: May 27, 2022

Many organometallic iridium(III) complexes have photoactive excited states with mixed metal-to-ligand and intraligand charge transfer (MLCT/ILCT) character, which form the basis for numerous applications in photophysics photochemistry. Cobalt(III) analogous MLCT excited-state properties seem to be unknown yet, despite fact that cobalt(III) can adopt identical low-spin d6 valence electron configurations due their close chemical relationship. Using a rigid tridentate chelate ligand (LCNC), central amido π-donor is flanked by two σ-donating N-heterocyclic carbene subunits, we obtained robust homoleptic complex [Co(LCNC)2](PF6), featuring state substantial character. Compared vast majority of isoelectronic iron(II) complexes, [Co(LCNC)2](PF6) long-lived because it does not deactivate as efficiently into lower-lying metal-centered states; furthermore, engages directly photoinduced reactions. The comparison [Fe(LCNC)2](PF6), well structural, electrochemical, UV–vis transient absorption studies, provides insight new design principles first-row transition-metal photophysical photochemical reminiscent those known from platinum group metals.

Language: Английский

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Sensitization-initiated electron transfer via upconversion: mechanism and photocatalytic applications

Chemical Science, Journal Year: 2021, Volume and Issue: 12(29), P. 9922 - 9933

Published: Jan. 1, 2021

A full picture of a new multi-photon excitation mechanism relying on sTTA upconversion is provided, together with selected photocatalytic applications. All mechanistic steps are investigated and the catalytically active species observed directly.

Language: Английский

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Shedding Light on the Oxidizing Properties of Spin-Flip Excited States in a Cr^III Polypyridine Complex and Their Use in Photoredox Catalysis

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 144(31), P. 14181 - 14194

Published: Aug. 1, 2022

The photoredox activity of well-known RuII complexes stems from metal-to-ligand charge transfer (MLCT) excited states, in which a ligand-based electron can initiate chemical reductions and metal-centered hole trigger oxidations. CrIII polypyridines show similar properties, although they have fundamentally different electronic structures. Their photoactive state is spin-flip nature, differing the ground merely by change one spin, but with otherwise identical d-orbital occupancy. We find that driving-force dependence for photoinduced 10 donors to complex very polypyridine, thereby validate concept estimating redox potential d3 states analogous manner as MLCT d6 compounds. Building on this insight, we use our photocatalytic reactions not previously explored compound class, including aerobic bromination methoxyaryls, oxygenation 1,1,2,2-tetraphenylethylene, hydroxylation arylboronic acids, vinylation N-phenyl pyrrolidine. This work contributes understanding fundamental photochemical properties first-row transition-metal comparison well-explored precious-metal-based photocatalysts.

Language: Английский

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