Iron Photoredox Catalysis–Past, Present, and Future

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(17), P. 9369 - 9388

Published: April 20, 2023

Photoredox catalysis of organic reactions driven by iron has attracted substantial attention throughout recent years, due to potential environmental and economic benefits. In this Perspective, three major strategies were identified that have been employed date achieve reactivities comparable the successful noble metal photoredox catalysis: (1) Direct replacement a center in archetypal polypyridyl complexes, resulting metal-centered photofunctional state. (2) situ generation photoactive complexes substrate coordination where are via intramolecular electron transfer involving charge-transfer states, for example, through visible-light-induced homolysis. (3) Improving excited-state lifetimes redox potentials states new ligand design. We seek give an overview evaluation developments rapidly growing field and, at same time, provide outlook on future iron-based catalysis.

Language: Английский

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Cage escape governs photoredox reaction rates and quantum yields

Nature Chemistry, Journal Year: 2024, Volume and Issue: 16(7), P. 1151 - 1159

Published: March 18, 2024

Abstract Photoredox catalysis relies on light-induced electron transfer leading to a radical pair comprising an oxidized donor and reduced acceptor in solvent cage. For productive onward reaction occur, the must escape from that cage before they undergo spontaneous reverse transfer. Here we show decisive role plays three benchmark photocatalytic reactions, namely, aerobic hydroxylation, reductive debromination aza-Henry reaction. Using ruthenium(II)- chromium(III)-based photocatalysts, which provide inherently different quantum yields, determined quantitative correlations between rates of photoredox product formation yields. These findings can be largely rationalized within framework Marcus theory for

Language: Английский

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Direct Observation of Triplet States in the Isomerization of Alkenylboronates by Energy Transfer Catalysis

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(39), P. 21576 - 21586

Published: Sept. 20, 2023

Alkenylboronates are versatile building blocks for stereocontrolled synthesis owing to the traceless nature of boron group that can be leveraged achieve highly selective geometric isomerization. Using thioxanthone as an inexpensive photocatalyst, photoisomerization these species continues provide expansive platform stereodivergent synthesis, particularly in construction bioactive polyenes. Although mechanistic investigations consistent with light-driven energy transfer, direct experimental evidence remains conspicuously absent. Herein, we report a rigorous investigation using two widely used alkenylboronates alongside relevant reference compounds. Through combination irradiation experiments, transient absorption spectroscopic studies, kinetic modeling, and DFT calculations all isomers model compounds, it has been possible unequivocally detect characterize perpendicular triplet generated by transfer. Our results serve not only blueprint studies challenging organic sensitizers, but guidelines delineated have also enabled development more sustainable reaction conditions: first time, efficient organocatalytic isomerization under sunlight become feasible.

Language: Английский

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Dicationic Acridinium/Carbene Hybrids as Strongly Oxidizing Photocatalysts

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(5), P. 3416 - 3426

Published: Jan. 24, 2024

A new design concept for organic, strongly oxidizing photocatalysts is described based upon dicationic acridinium/carbene hybrids. highly modular synthesis of such hybrids presented, and the dications are utilized as novel, tailor-made photoredox catalysts in direct oxidative C-N coupling. Under optimized conditions, benzene even electron-deficient arenes can be oxidized coupled with a range

Language: Английский

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Factors that Impact Photochemical Cage Escape Yields

Chemical Reviews, Journal Year: 2024, Volume and Issue: 124(11), P. 7379 - 7464

Published: May 14, 2024

The utilization of visible light to mediate chemical reactions in fluid solutions has applications that range from solar fuel production medicine and organic synthesis. These are typically initiated by electron transfer between a photoexcited dye molecule (a photosensitizer) redox-active quencher yield radical pairs intimately associated within solvent cage. Many these radicals undergo rapid thermodynamically favored "geminate" recombination do not diffuse out the cage surrounds them. Those escape useful reagents may subsequent important above-mentioned applications. process factors determine yields remain poorly understood despite decades research motivated their practical fundamental importance. Herein, state-of-the-art on light-induced appeared since seminal 1972 review J. P. Lorand entitled "The Cage Effect" is reviewed. This also provides some background for those new field discusses both homolytic bond photodissociation bimolecular induced reactions. concludes with key goals directions future promise elevate this very vibrant even greater heights.

Language: Английский

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Iron(III) Carbene Complexes with Tunable Excited State Energies for Photoredox and Upconversion

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: unknown

Published: April 10, 2024

Substituting precious elements in luminophores and photocatalysts by abundant first-row transition metals remains a significant challenge, iron continues to be particularly attractive owing its high natural abundance low cost. Most complexes known date face severe limitations due undesirably efficient deactivation of luminescent photoredox-active excited states. Two new iron(III) with structurally simple chelate ligands enable straightforward tuning ground state properties, contrasting recent examples, which chemical modification had minor impact. Crude samples feature two luminescence bands strongly reminiscent complex, this observation was attributed dual luminescence, but our case, there is clear-cut evidence that the higher-energy stems from an impurity only red photoluminescence doublet ligand-to-metal charge transfer (2LMCT) genuine. Photoinduced oxidative reductive electron reactions methyl viologen 10-methylphenothiazine occur nearly diffusion-limited kinetics. Photocatalytic not previously reported for compound class, particular C–H arylation diazonium salts aerobic hydroxylation boronic acids, were achieved low-energy light excitation. Doublet–triplet energy (DTET) 2LMCT anthracene annihilator permits proof principle triplet–triplet annihilation upconversion based on molecular photosensitizer. These findings are relevant development featuring photophysical photochemical properties competitive noble-metal-based compounds.

Language: Английский

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Investigation of the Excited-State Electron Transfer and Cage Escape Yields Between Halides and a Fe(III) Photosensitizer

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(15), P. 10286 - 10292

Published: April 3, 2024

Excited-state quenching and reduction of [Fe(phtmeimb)2]+, where phtmeimb is phenyl[tris(3-methyl-imidazolin-2-ylidene)]borate, with iodide, bromide, chloride were studied in dichloromethane, acetonitrile, acetonitrile/water 1:1 mixture by means steady-state time-resolved spectroscopic techniques. Quenching rate constants almost diffusion-limited dichloromethane acetonitrile followed the expected periodic trend, i.e., I– > Br– Cl–. Confirmation excited-state reductive electron transfer was only unambiguously obtained when iodide used as a quencher. The cage escape yields, separation geminate radical pair formed upon bimolecular transfer, determined. These yields larger (0.079) than (0.017), no photoproduct could be observed 1:1. This study further emphasizes that solvents low dielectric constant are more suited for productive using Fe(III) photosensitizers 2LMCT excited state.

Language: Английский

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Aminomethylations of electron-deficient compounds—bringing iron photoredox catalysis into play

Chemical Science, Journal Year: 2024, Volume and Issue: 15(30), P. 12077 - 12085

Published: Jan. 1, 2024

Electron transfer to the 2 LMCT state of a photoactive complex based on Earth-abundant iron has been used drive photocatalytic aminomethylation reactions by generation α-aminoalkyl radicals and underlying mechanism investigated.

Language: Английский

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A protocol for determining cage-escape yields using nanosecond transient absorption spectroscopy

STAR Protocols, Journal Year: 2023, Volume and Issue: 4(2), P. 102312 - 102312

Published: May 15, 2023

Here, we present a protocol for the determination of cage-escape yields following excited-state electron transfer between photosensitizer and quencher. We describe steps determining changes in molar absorption coefficient different oxidation states via photolysis experiments percentage reacted species steady-state or time-resolved spectroscopy. then detail measurement amount formed product nanosecond transient For complete details on use execution this protocol, please refer to Ripak et al. (2023).1.

Language: Английский

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Spectroscopic Techniques to Unravel Mechanistic Details in Light‐Induced Transformations and Photoredox Catalysis

ChemCatChem, Journal Year: 2023, Volume and Issue: 16(1)

Published: Nov. 9, 2023

Abstract The rapid development of photo(redox) catalysis within the last decades is remarkable to extent that utilization light‐driven processes in organic chemistry has become a credible alternative current thermal processes. Such advances offer tremendous opportunities collaborations between scientific realms can have drastic impact on field. In this concept article, special emphasis placed spectroscopic techniques are used, or could be for light‐induced transformations and photoredox applications. These include spectroelectrochemistry, UV‐VIS, IR X‐Ray transient absorption spectroscopy, laser pulsed radiolysis (PR), photo‐induced chemically induced dynamic nuclear polarization (Photo‐CIDNP), photoacoustic time‐resolved Raman spectroscopy (TRRS), Electron Paramagnetic Resonance (TREPR) dielectric loss (TRDL). theoretical background behind each technique briefly introduced followed by selected relevant examples from literature.

Language: Английский

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