Ligand‐to‐Metal Charge Transfer (LMCT) Photochemistry at 3d‐Metal Complexes: An Emerging Tool for Sustainable Organic Synthesis

ChemCatChem, Год журнала: 2022, Номер 14(19)

Опубликована: Авг. 11, 2022

Abstract Despite the rich photochemistry of 3d‐metal complexes, utilization excited‐state reactivity these compounds in organic synthesis has been historically overlooked. The advent photoredox catalysis changed perception synthetic chemists towards photochemistry, and nowadays potential photoinduced, outer‐sphere single‐electron transfer events is widely recognized. More recently, an emerging new mode photoactivation taken spotlight, based on inner‐sphere triggered by population ligand‐to‐metal charge‐transfer (LMCT) excited states. Contrarily to photoredox, LMCT‐activation does not rely matching redox potentials, offers unique profiles particularly well suited Earth‐abundant metal complexes. Those appealing features are propelling development methods using this blueprint generate highly reactive open‐shell species under mild conditions. aim contribution provide a didactical tool for comprehension concept facilitate methodologies achieve sustainable chemical transformations.

Язык: Английский

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Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d⁶ Complexes with Cr⁰, Mn^I, Fe^II, and Co^III

Journal of the American Chemical Society, Год журнала: 2023, Номер 145(9), С. 4903 - 4920

Опубликована: Фев. 21, 2023

Many coordination complexes and organometallic compounds with the 4d6 5d6 valence electron configurations have outstanding photophysical photochemical properties, which stem from metal-to-ligand charge transfer (MLCT) excited states. This substance class makes extensive use of most precious least abundant metal elements, consequently there has been a long-standing interest in first-row transition photoactive MLCT Semiprecious copper(I) its completely filled 3d subshell is relatively straightforward well explored case, but 3d6 partially d-orbitals lead to energetically low-lying metal-centered (MC) states that can cause undesirably fast state deactivation. Herein, we discuss recent advances made isoelectronic Cr0, MnI, FeII, CoIII compounds, for long-lived become accessible over past five years. Furthermore, possible future developments search new subshells next-generation applications photophysics photochemistry.

Язык: Английский

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Covalent‐Bonding Oxidation Group and Titanium Cluster to Synthesize a Porous Crystalline Catalyst for Selective Photo‐Oxidation Biomass Valorization

Angewandte Chemie International Edition, Год журнала: 2022, Номер 61(37)

Опубликована: Июль 19, 2022

The selective photo-oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is important due its substitute-role in polyester-fabrication. Here, a titanium-cluster based metal-covalent organic framework nanosheet has been synthesized through the covalent-coupling between Ti6 -NH2 and benzotrithiophene tricarbaldehyde (BTT). integration them endows with visible-light-adsorption region, effective electron-hole separation-efficiency suitable ability. Specifically, photo-selectivity for HMF-to-FDCA can be >95 % ≈100 conversion, which more than 2, 5, 10 times higher MOF-901 (43 %), (19 %) under-darkness (9 respectively. Notably, an O2 -based mechanism proposed vital roles BTT are verified by DFT calculations. This work might facilitate exploration porous-crystalline-catalysts biomass-valorization.

Язык: Английский

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Mechanisms of Photoredox Catalysis Featuring Nickel–Bipyridine Complexes

ACS Catalysis, Год журнала: 2024, Номер 14(11), С. 9055 - 9076

Опубликована: Май 29, 2024

Metallaphotoredox catalysis can unlock useful pathways for transforming organic reactants into desirable products, largely due to the conversion of photon energy chemical potential drive redox and bond transformation processes. Despite importance these processes cross-coupling reactions other transformations, their mechanistic details are only superficially understood. In this review, we have provided a detailed summary various photoredox mechanisms that been proposed date Ni-bipyridine (bpy) complexes, focusing separately on photosensitized direct excitation reaction By highlighting multiple key findings, depict how mechanisms, which ultimately define substrate scope, themselves defined by ground- excited-state geometric electronic structures Ni-based intermediates. We further identify knowledge gaps motivate future studies development synergistic research approaches spanning physical, organic, inorganic chemistry communities.

Язык: Английский

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Mechanism of Ni-Catalyzed Photochemical Halogen Atom-Mediated C(sp³)–H Arylation

Journal of the American Chemical Society, Год журнала: 2024, Номер 146(22), С. 15331 - 15344

Опубликована: Май 23, 2024

Within the context of Ni photoredox catalysis, halogen atom photoelimination from has emerged as a fruitful strategy for enabling hydrogen transfer (HAT)-mediated C(sp3)–H functionalization. Despite numerous synthetic transformations invoking this paradigm, unified mechanistic hypothesis that is consistent with experimental findings on catalytic systems and accounts radical formation facile C(sp2)–C(sp3) bond remains elusive. We employ kinetic analysis, organometallic synthesis, computational investigations to decipher mechanism prototypical Ni-catalyzed photochemical arylation reaction. Our revise previous proposals, first by examining relevance SET EnT processes intermediates relevant HAT-based investigation highlights ability blue light promote efficient Ni–C(sp2) homolysis cationic NiIII reductive elimination bipyridine NiII complexes. However interesting, rates selectivities these do not account productive pathway. Instead, our studies support involves evolution in situ generated dihalide intermediates, capture NiII(aryl)(halide) resting state, key C–C NiIII. Oxidative addition NiI, opposed Ni0, rapid NiIII/NiI comproportionation play roles process. The presented herein offer fundamental insight into reactivity broader catalysis.

Язык: Английский

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Catalysis in the Excited State: Bringing Innate Transition Metal Photochemistry into Play

ACS Catalysis, Год журнала: 2025, Номер unknown, С. 4665 - 4680

Опубликована: Март 5, 2025

Transition metal catalysis is an indispensable tool for organic synthesis that has been harnessed, modulated, and perfected many decades by careful selection of centers ligands, giving rise to synthetic methods with unparalleled efficiency chemoselectivity. Recent developments have demonstrated how light irradiation can also be recruited as a powerful dramatically alter the outcome catalytic reactions, providing access innovative pathways remarkable potential. In this context, adoption photochemical conditions mainstream strategy drive reactions unveiled exciting opportunities exploit rich excited-state framework transition metals applications. This Perspective examines advances in application complexes standalone photocatalysts, exploiting innate reactivity their excited states beyond common use photoredox catalysts. An account relevant examples dissected provide discussion on electronic reorganization, orbitals involved, associated different types states. analysis aims practitioners fundamental principles guiding strategies understand, design, apply light-activation homogeneous synthesis.

Язык: Английский

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Overcoming Photochemical Limitations in Metallaphotoredox Catalysis: Red-Light-Driven C–N Cross-Coupling

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(49), С. 22409 - 22415

Опубликована: Ноя. 23, 2022

Aryl amination is an essential transformation for medicinal, process, and materials chemistry. In addition to classic Buchwald–Hartwig conditions, blue-light-driven metallaphotoredox catalysis has emerged as a valuable tool C–N cross-coupling. However, blue light suffers from low penetration through reaction media, limiting its scalability industrial purposes. addition, enhances unwanted side-product formation in catalysis, namely hydrodehalogenation. Low-energy light, such deep red (DR) or near-infrared (NIR), offers solution this problem it can provide enhanced media compared higher-energy wavelengths. Herein, we show that low-energy also enhance the desired reactivity by suppressing We hypothesize reduced side product formed direct photolysis of aryl–nickel bond high-energy leading generation aryl radicals. Using deep-red osmium photocatalyst, demonstrate scope (hetero)aryl bromides amine-based nucleophiles with minimal hydrodehalogenation byproducts.

Язык: Английский

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Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

JACS Au, Год журнала: 2022, Номер 2(10), С. 2367 - 2380

Опубликована: Окт. 11, 2022

Many CuI complexes have luminescent triplet charge-transfer excited states with diverse applications in photophysics and photochemistry, but for isoelectronic ZnII compounds, this behavior is much less common, they typically only show ligand-based fluorescence from singlet π–π* states. We report two closely related tetrahedral which intersystem crossing occurs appreciable quantum yields leads to the population of intraligand (ILCT) character. In addition showing their initially 1ILCT states, these new compounds therefore undergo triplet–triplet energy transfer (TTET) 3ILCT consequently can act as sensitizers photo-isomerization reactions annihilation upconversion blue ultraviolet spectral range. The photoactive state furthermore facilitates photoinduced electron transfer. Collectively, our findings demonstrate that mononuclear photophysical photochemical properties reminiscent well-known are accessible suitable ligands potentially amenable many different applications. Our insights seem relevant greater context obtaining based on abundant transition metals, complementing precious-metal-based luminophores photosensitizers.

Язык: Английский

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Intraligand Charge Transfer Enables Visible‐Light‐Mediated Nickel‐Catalyzed Cross‐Coupling Reactions**

Angewandte Chemie International Edition, Год журнала: 2022, Номер 61(46)

Опубликована: Сен. 26, 2022

We demonstrate that several visible-light-mediated carbon-heteroatom cross-coupling reactions can be carried out using a photoactive NiII precatalyst forms in situ from nickel salt and bipyridine ligand decorated with two carbazole groups (Ni(Czbpy)Cl2 ). The activation of this towards follows hitherto undisclosed mechanism is different previously reported light-responsive complexes undergo metal-to-ligand charge transfer. Theoretical spectroscopic investigations revealed irradiation Ni(Czbpy)Cl2 visible light causes an initial intraligand transfer event triggers productive catalysis. Ligand polymerization affords porous, recyclable organic polymer for heterogeneous catalysis reactions. catalyst shows stable performance packed-bed flow reactor during week continuous operation.

Язык: Английский

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Molecular Design Principles to Elongate the Metal-to-Ligand Charge Transfer Excited-State Lifetimes of Square-Planar Nickel(II) Complexes

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(48), С. 21948 - 21960

Опубликована: Ноя. 23, 2022

Square-planar NiII complexes and their electronically excited states play key roles in cross-coupling catalysis could offer new opportunities to complement well-known isoelectronic PtII luminophores. Metal-to-ligand charge transfer (MLCT) deactivation pathways are particularly relevant these contexts. We sought extend the lifetimes of 3MLCT square-planar by creating coordination environments that seemed well adapted 3d8 valence electron configuration. Using a rigid tridentate chelate ligand, which central cyclometalated phenyl unit is flanked two coordinating N-heterocyclic carbenes, along with monodentate isocyanide very strong ligand field created. Bulky substituents at backbone furthermore protect center from nucleophilic attack axial directions. UV-Vis transient absorption spectroscopies reveal upon excitation into 1MLCT bands ultrafast intersystem crossing state, latter relaxes onward metal-centered triplet state (3MC). A torsional motion NiII-carbon bond elongation facilitate relaxation 3MC state. The lifetime gets longer increasing strength improved steric protection, thereby revealing clear design guidelines for enhanced photophysical properties. longest reached solution room temperature 48 ps, factor 5-10 compared previously investigated complexes. Our study contributes making first-row transition metal partially filled d-orbitals more amenable applications photophysics photochemistry.

Язык: Английский

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