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

Chemical Reviews, Год журнала: 2021, Номер 122(2), С. 2487 - 2649

Опубликована: Ноя. 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.

Язык: Английский

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Luminescent First-Row Transition Metal Complexes

JACS Au, Год журнала: 2021, Номер 1(11), С. 1860 - 1876

Опубликована: Сен. 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.

Язык: 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, Год журнала: 2021, Номер 143(29), С. 10882 - 10889

Опубликована: Июль 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.

Язык: 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, Год журнала: 2021, Номер 143(33), С. 13266 - 13273

Опубликована: Авг. 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.

Язык: Английский

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

Nature Chemistry, Год журнала: 2023, Номер 15(6), С. 794 - 802

Опубликована: Март 23, 2023

Язык: Английский

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

Nature Chemistry, Год журнала: 2023, Номер 15(12), С. 1730 - 1736

Опубликована: Авг. 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.

Язык: Английский

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

Angewandte Chemie International Edition, Год журнала: 2021, Номер 60(39), С. 21418 - 21425

Опубликована: Июль 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.

Язык: 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, Год журнала: 2022, Номер 144(22), С. 9859 - 9873

Опубликована: Май 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.

Язык: Английский

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

Chemical Science, Год журнала: 2021, Номер 12(29), С. 9922 - 9933

Опубликована: Янв. 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.

Язык: Английский

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High Triplet Energy Iridium(III) Isocyanoborato Complex for Photochemical Upconversion, Photoredox and Energy Transfer Catalysis

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(2), С. 963 - 976

Опубликована: Янв. 5, 2022

Cyclometalated Ir(III) complexes are often chosen as catalysts for challenging photoredox and triplet-triplet-energy-transfer (TTET) catalyzed reactions, they of interest upconversion into the ultraviolet spectral range. However, triplet energies commonly employed photosensitizers typically limited to values around 2.5-2.75 eV. Here, we report on a new luminophore, with an unusually high energy near 3.0 eV owing modification previously reported complex isocyanoborato ligands. Compared nonborylated cyanido precursor complex, introduction B(C6F5)3 units in second coordination sphere results substantially improved photophysical properties, particular luminescence quantum yield (0.87) long excited-state lifetime (13.0 μs), addition energy. These favorable properties (including good long-term photostability) facilitate exceptionally organic photoreactions (sensitized) triplet-triplet annihilation fluorescent singlet excited state beyond 4 eV, deep region. The photocatalyzes sigmatropic shift [2 + 2] cycloaddition reactions that unattainable common transition metal-based photosensitizers. In presence sacrificial electron donor, it furthermore is applicable demanding photoreductions, including dehalogenations, detosylations, degradation lignin model substrate. Our study demonstrates how rational ligand design transition-metal underexplored effects) can be used enhance their thereby broaden application potential solar conversion synthetic photochemistry.

Язык: Английский

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