Mechanisms of Photoredox Catalysis Featuring Nickel–Bipyridine Complexes

ACS Catalysis, Journal Year: 2024, Volume and Issue: 14(11), P. 9055 - 9076

Published: May 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.

Language: Английский

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

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(22), P. 15331 - 15344

Published: May 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.

Language: Английский

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Ligand-Enabled “Two-in-One” Metallaphotocatalytic Cross Couplings

ACS Catalysis, Journal Year: 2025, Volume and Issue: 15(3), P. 1635 - 1654

Published: Jan. 15, 2025

Metallaphotoredox cross coupling (MCC) is ranking among the most advanced synthetic methodology as it can access chemical space that difficult to attain under conventional conditions. Earlier developed MCC mandates an independent transition metal catalyst and respective photocatalyst, thus constituting a dual catalytic manifold. Complementarily, paradigm-shifting metallaphotoredox strategy capitalizes on single photoreactive complex emerging, which brings not only operational simplification but also unexpected mechanistic insights. This perspective compiled recent advances in monocatalytic couplings categorized them based ligands confer distinct photoreactivities various mechanisms. To this end, ligand-enabled oxidative addition, transmetalation, reductive elimination other radical-involving pathways were summarized with notable examples. In way, we wish provide handy guideline for readers who are interested emerging field inspire more future endeavors MCCs beyond.

Language: Английский

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Nickel-mediated aerobic C(sp2)–nucleophile coupling reactions for late-stage diversification of aryl electrophiles

Nature Synthesis, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 16, 2025

Language: Английский

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Photogenerated Ni(I)–Bipyridine Halide Complexes: Structure–Function Relationships for Competitive C(sp²)–Cl Oxidative Addition and Dimerization Reactivity Pathways

Inorganic Chemistry, Journal Year: 2023, Volume and Issue: 62(24), P. 9538 - 9551

Published: June 6, 2023

We report the facile photochemical generation of a library Ni(I)-bpy halide complexes (Ni(I)(Rbpy)X (R = t-Bu, H, MeOOC; X Cl, Br, I) and benchmark their relative reactivity toward competitive oxidative addition off-cycle dimerization pathways. Structure-function relationships between ligand set are developed, with particular emphasis on rationalizing previously uncharacterized ligand-controlled high energy challenging C(sp2)-Cl bonds. Through dual Hammett computational analysis, mechanism formal is found to proceed through an SNAr-type pathway, consisting nucleophilic two-electron transfer Ni(I) 3d(z2) orbital Caryl-Cl σ* orbital, which contrasts observed for activation weaker C(sp2)-Br/I The bpy substituent provides strong influence reactivity, ultimately determining whether or even occurs. Here, we elucidate origin this as arising from perturbations effective nuclear charge (Zeff) center. Electron donation metal decreases Zeff, leads significant destabilization entire 3d manifold. Decreasing electron binding energies powerful donor activate These changes also prove have analogous effect dimerization, in Zeff leading more rapid dimerization. Ligand-induced modulation thus tunable target by can be altered, providing direct route stimulate stronger C-X bonds potentially unveiling new ways accomplish Ni-mediated photocatalytic cycles.

Language: Английский

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Werner Salt as Nickel and Ammonia Source for Photochemical Synthesis of Primary Aryl Amines

Angewandte Chemie International Edition, Journal Year: 2023, Volume and Issue: 63(6)

Published: Nov. 2, 2023

Cheap, stable and easy-to-handle Werner ammine salts have been known for more than a century; but they rarely used in organic synthesis. Herein, we report that the hexammine complex [Ni(NH

Language: Английский

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Leveraging the Redox Promiscuity of Nickel To Catalyze C–N Coupling Reactions

The Journal of Organic Chemistry, Journal Year: 2024, Volume and Issue: unknown

Published: Jan. 17, 2024

This perspective details advances made in the field of Ni-catalyzed C–N bond formation. The use this Earth abundant metal to decorate amines, amides, lactams, and heterocycles enables direct access a variety biologically active industrially relevant compounds sustainable manner. Herein, different strategies that leverage propensity Ni facilitate both one- two-electron processes will be surveyed. first part Perspective focuses on couplings at room temperature by accessing oxidized Ni(III) intermediates. In context, photochemical, electrochemical, chemically mediated analyzed. A special emphasis has been put providing comprehensive explanation mechanistic avenues have proposed these chemistries; either Ni(I/III) self-sustained cycles or Ni(0/II/III) photochemically pathways. second ligand designs also enable reactivity via Ni(0/II) mechanism. Finally, we discuss our thoughts possible future directions field.

Language: Английский

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Nickel/Photoredox-Catalyzed Direct Amidation of Aldehydes with Nitroarenes via Fully Catalytic Process

Organic Letters, Journal Year: 2023, Volume and Issue: 25(24), P. 4592 - 4597

Published: June 12, 2023

A fully catalytic nickel-photoredox process for the direct amidation of aldehydes with nitroarenes was developed. In this system, and were catalytically activated by photocatalytic cycle without addition an additional reductant or oxidants, which facilitated Ni-mediated cross-coupling C-N bond under mild conditions. preliminary mechanistic study indicates a reaction pathway in nitrobenzene is directly reduced to aniline as nitrogen source.

Language: Английский

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Mechanistic Evidence of a Ni(0/II/III) Cycle for Nickel Photoredox Amide Arylation

Angewandte Chemie International Edition, Journal Year: 2023, Volume and Issue: 62(43)

Published: Sept. 9, 2023

This work demonstrates the dominance of a Ni(0/II/III) cycle for Ni-photoredox amide arylation, which contrasts with other C-heteroatom couplings that operate via Ni(I/III) self-sustained cycles. The kinetic data gathered when using different Ni precatalysts supports an initial Ni(0)-mediated oxidative addition into aryl bromide. Using NiCl2 as precatalyst resulted in observable induction period, was found to arise from photochemical activation event generate Ni(0) and be prolonged by unproductive comproportionation between Ni(II) situ generated active species. Ligand exchange after yields amido complex, identified catalyst resting state reaction. Stoichiometric experiments showed oxidation this intermediate required yield functionalized products. presented rate-limiting photochemically-mediated Ni(II/III) enable C-N reductive elimination. An alternative manifold discarded based on EPR measurements. mechanistic insights uncovered herein will inform community how subtle changes reaction conditions may impact pathway, have enabled us include chlorides coupling partners reduce loading 20-fold without any reactivity loss.

Language: Английский

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Light-Promoted Efficient Generation of Fe(I) to Initiate Amination

ACS Catalysis, Journal Year: 2024, Volume and Issue: 14(7), P. 4968 - 4974

Published: March 18, 2024

Iron-catalyzed cross-coupling reactions are difficult to achieve because they usually require a highly reactive, low-valent iron catalyst undergo the oxidative addition process. Here, we report method for light-promoted iron-catalyzed C–N coupling between aryl bromides and amines in presence of catalytic amount bipyridine ligand under irradiation at 390–395 nm. This method, which does not external photosensitizers, features broad substrate scope (70 examples) good functional group tolerance, providing platform development organic synthesis. Mechanistic studies indicate that an base light crucial generation Fe(I) species reaction involves Fe(I)/Fe(III) cycle.

Language: Английский

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