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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Cross-Electrophile Coupling: Principles, Methods, and Applications in Synthesis

Chemical Reviews, Journal Year: 2024, Volume and Issue: unknown

Published: Nov. 26, 2024

Cross-electrophile coupling (XEC), defined by us as the cross-coupling of two different σ-electrophiles that is driven catalyst reduction, has seen rapid progression in recent years. As such, this review aims to summarize field from its beginnings up until mid-2023 and provide comprehensive coverage on synthetic methods current state mechanistic understanding. Chapters are split type bond formed, which include C(sp

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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Synthesis of Nickel(I)–Bromide Complexes via Oxidation and Ligand Displacement: Evaluation of Ligand Effects on Speciation and Reactivity

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(35), P. 19368 - 19377

Published: Aug. 23, 2023

Nickel’s +1 oxidation state has received much interest due to its varied and often enigmatic behavior in increasingly popular catalytic methods. In part, the lack of understanding about NiI results from common synthetic strategies limiting breadth complexes that are accessible for mechanistic study catalyst design. We report an oxidative approach using tribromide salts allows generation a well-defined precursor, [NiI(COD)Br]2, as well several new complexes. Included among them bearing bulky monophosphines, which structure–speciation relationships established reactivity Suzuki–Miyaura coupling (SMC) is investigated. Notably, these routes also allow synthesis monomeric t-Bubpy-bound complexes, not previously been achieved. These react with aryl halides, can enable challenging investigations present opportunities catalysis synthesis.

Language: Английский

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Nickel-Catalyzed Enantioselective Reductive Arylation of Common Ketones

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(19), P. 12895 - 12900

Published: May 2, 2024

A nickel complex of chiral bisoxazolines catalyzed the stereoselective reductive arylation ketones in high enantioselectivity. range common acyclic and cyclic reacted without aid directing groups. Mechanistic studies using isolated a bis(oxazoline) (L)Ni(Ar)Br revealed that Mn reduction was not needed, while Lewis acidic titanium alkoxides were critical to ketone insertion.

Language: Английский

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Sulfonyl hydrazides as a general redox-neutral platform for radical cross-coupling

Science, Journal Year: 2025, Volume and Issue: unknown

Published: March 6, 2025

Language: Английский

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Ultrafast Photophysics of Ni(I)–Bipyridine Halide Complexes: Spanning the Marcus Normal and Inverted Regimes

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(22), P. 15506 - 15514

Published: May 22, 2024

Owing to their light-harvesting properties, nickel–bipyridine (bpy) complexes have found wide use in metallaphotoredox cross-coupling reactions. Key these transformations are Ni(I)–bpy halide intermediates that absorb a significant fraction of light at relevant reaction irradiation wavelengths. Herein, we report ultrafast transient absorption (TA) spectroscopy on library eight complexes, the first such characterization any Ni(I) species. The TA data reveal formation and decay Ni(I)-to-bpy metal-to-ligand charge transfer (MLCT) excited states (10–30 ps) whose relaxation dynamics well described by vibronic Marcus theory, spanning normal inverted regions as result simple changes bpy substituents. While lifetimes relatively long for MLCT first-row transition metal duration precludes excited-state bimolecular reactivity photoredox We also present one-step method generate an isolable, solid-state species, which decouples light-initiated from dark, thermal cycles catalysis.

Language: Английский

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Light Activation and Photophysics of a Structurally Constrained Nickel(II)–Bipyridine Aryl Halide Complex

Inorganic Chemistry, Journal Year: 2024, Volume and Issue: 63(9), P. 4120 - 4131

Published: Feb. 20, 2024

Transition-metal photoredox catalysis has transformed organic synthesis by harnessing light to construct complex molecules. Nickel(II)–bipyridine (bpy) aryl halide complexes are a significant class of cross-coupling catalysts that can be activated via direct excitation. This study investigates the effects molecular structure on photophysics these considering an underexplored, structurally constrained Ni(II)–bpy in which and bpy ligands covalently tethered alongside traditional unconstrained complexes. Intriguingly, is photochemically stable but features reversible Ni(II)–C(aryl) ⇄ [Ni(I)···C(aryl)•] equilibrium upon photoexcitation. When electrophile introduced during photoirradiation, we demonstrate preference for photodissociation over recombination, rendering parent Ni(II) source reactive Ni(I) intermediate. Here, characterize photochemical behavior kinetic analyses, quantum chemical calculations, ultrafast transient absorption spectroscopy. Comparison previously characterized indicates structural constraints considered here dramatically influence excited state relaxation pathway provide insight into characteristics excited-state Ni(II)–C bond homolysis radical reassociation dynamics. enriches understanding offers new possibilities designing customized photoactive precise synthesis.

Language: Английский

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Reconceptualizing the Ir^III Role in Metallaphotoredox Catalysis: From Strong Photooxidant to Potent Energy Donor

ACS Catalysis, Journal Year: 2024, Volume and Issue: 14(15), P. 11378 - 11388

Published: July 16, 2024

Dual IrIII/LnNiII metallaphotoredox catalyzed C(sp3)–C(sp2) cross-coupling reactions are widely assumed to proceed by photoinduced single electron transfer steps due the highly oxidizing IrIII* excited state (IrIII = [Ir(dF(CF3)ppy)2(dtbbpy)]+[PF6]−; dF(CF3)ppy 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine; Ln dtbbpy 4,4′-di-tert-butyl-2,2′-bipyridine). Using time-resolved absorption and emission spectroscopy, we reveal that energy between various LnNiII precatalysts intermediates with kq ≥ 108 M–1 s–1 also drives catalysis. Specifically, states of dihalide precatalysts/organometallic accessible appear drive bond homolysis, halogen radical elimination, reductive elimination facilitate formation cross-coupled products. Energy dynamics consequently circumvent need for transfer, thereby extending substrate scopes coupling partners cannot be oxidized IrIII*. Within a cross-electrophile model reaction 4-bromobenzotrifluoride bromocyclohexane, activates precatalyst at early times before nucleophilic reductants present. In absence IrIII, direct excitation LnNiII(Br)2 form LnNiII(Br)(Aryl) intermediate. To compare kinetics, determined rate constants quenching Br– (kSET 4.1 × s–1) subsequent from reduced IrIII•– 107 using Stern-Volmer analysis pulse radiolysis, respectively. competitive is parallel pathway within Exploiting mechanism, demonstrate selective 4-chlorobenzotrifluoride bromocyclohexane exclusively product. With alkyl-trifluoroborate nucleophiles do not reductively quench emission, transmetalation LnNiII(Br/Cl)(Aryl) followed Similarly, rather than NiII oxidation C(sp2)–OR despite strongly ability total, these processes in catalysis can unlock alternative reactive pathways.

Language: Английский

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Electronic Structures of Nickel(II)-Bis(indanyloxazoline)-dihalide Catalysts: Understanding Ligand Field Contributions That Promote C(sp²)–C(sp³) Cross-Coupling

Inorganic Chemistry, Journal Year: 2023, Volume and Issue: 62(34), P. 14010 - 14027

Published: Aug. 16, 2023

NiII(IB) dihalide [IB = (3aR,3a′R,8aS,8a′S)-2,2′-(cyclopropane-1,1-diyl)bis(3a,8a-dihydro-8H-indeno[1,2-d]-oxazole)] complexes are representative of a growing class first-row transition-metal catalysts for the enantioselective reductive cross-coupling C(sp2) and C(sp3) electrophiles. Recent mechanistic studies highlight complexity these ground-state cross-couplings but also illuminate new reactivity pathways stemming from one-electron redox their significant sensitivities to reaction conditions. For first time, diverse array spectroscopic methods coupled electrochemistry have been applied NiII-based precatalysts evaluate specific ligand field effects governing key Ni-based potentials. We experimentally demonstrate DMA solvent coordination catalytically relevant Ni complexes. Coordination is shown favorably influence redox-based steps prevent other deleterious equilibria. Combined with electronic structure calculations, we further provide direct correlation between intermediate frontier molecular orbital energies yields. Considerations developed herein use synergic electrochemical concepts catalyst design rationalization condition optimization.

Language: Английский

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