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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Comproportionation and disproportionation in nickel and copper complexes

Chemical Society Reviews, Journal Year: 2023, Volume and Issue: 52(19), P. 6601 - 6616

Published: Jan. 1, 2023

This review covers factors that contribute to comproportionation and disproportionation reactions in transition metal complexes provide insight into the importance of these electron transfer events Ni- Cu-catalyzed transformations.

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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Effect of 6,6′-Substituents on Bipyridine-Ligated Ni Catalysts for Cross-Electrophile Coupling

ACS Catalysis, Journal Year: 2024, Volume and Issue: 14(9), P. 6897 - 6914

Published: April 19, 2024

A family of 4,4′-tBu2-2,2′-bipyridine (tBubpy) ligands with substituents in either the 6-position, 4,4′-tBu2-6-Me-bpy (tBubpyMe), or 6 and 6′-positions, 4,4′-tBu2-6,6′-R2-bpy (tBubpyR2; R = Me, iPr, sBu, Ph, Mes), was synthesized. These were used to prepare Ni complexes 0, I, II oxidation states. We observed that 6′-positions tBubpy ligand impact properties complexes. For example, bulkier 6,6′-positions better stabilized (tBubpyR2)NiICl species resulted a cleaner reduction from (tBubpyR2)NiIICl2. However, hindered prevented coordination tBubpyR2 Ni0(cod)2. In addition, by using type (tBubpyMe)NiCl2 (tBubpyR2)NiCl2 as precatalysts for different XEC reactions, we demonstrated 6,6′-substituents lead major differences catalytic performance. Specifically, while (tBubpyMe)NiIICl2 is one most active catalysts reported date can facilitate reactions at room temperature, lower turnover frequencies containing ligands. detailed study on intermediates (tBubpy)Ni(Ar)I (tBubpyMe2)Ni(Ar)I revealed several factors likely contributed activity. whereas are low spin relatively stable, high-spin less stable. Furthermore, captures primary benzylic alkyl radicals more slowly than (tBubpy)Ni(Ar)I, consistent activity former catalysis. Our findings will assist design tailor-made Ni-catalyzed transformations.

Language: Английский

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Radicalizing CO by Mononuclear Palladium(I)

Angewandte Chemie International Edition, Journal Year: 2024, Volume and Issue: 63(19)

Published: March 18, 2024

Abstract A mononuclear, T‐shaped palladium(I) d 9 metalloradical ( 3 ), stabilized by a bulky carbazole‐based PNP‐ligand, was obtained reduction of palladium chloride or thermal Pd−C bond homolysis the corresponding neopentyl complex. Pressurizing with CO gave Pd(I) carbonyl complex, which structurally characterized X‐ray diffraction. Delocalization unpaired electron to carbon detected EPR spectroscopy and theoretically modeled DFT ab initio methods. The partially reduced radicalized slowly reacts di( tert ‐butyl) disulfide under homolytic S−S cleavage C−S formation give metallathioester.

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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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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Nickel-catalyzed reductive alkynylation of ketoimines via unstrained C–C bond activation

Chinese Chemical Letters, Journal Year: 2025, Volume and Issue: unknown, P. 111050 - 111050

Published: March 1, 2025

Language: Английский

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Unraveling a Complex Mechanistic Picture of Photochemical Nickel-Catalyzed THF Arylation through Product Enantioselectivity Analysis

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

Published: May 6, 2025

Abstract This study provides a comprehensive mechanistic understanding of asymmetric THF α-O-arylation via Ni photochemical catalysis, leveraging enantioinduction data to refine the reaction pathway. Originally reported in racemic fashion by Molander and Doyle, this transformation was re-examined using chiral bis(oxazoline) ligands, revealing distinct enantioselectivity trends depending on halogen present aryl halide pre-catalyst. Stoichiometric experiments demonstrated that Ni(II) oxidative addition complex is primarily responsible for trapping radical, while multivariate linear regression modeling confirmed remains coordinated during enantiodetermining step. Time-course uncovered an alternative initial pathway when Ni(0) used as pre-catalyst, which ultimately converged main EPR analysis further revealed rapid comproportionation between Ni(II), forming Ni(I) species engage radical at early stages, accounting observed reactivity differences. By integrating with experimental techniques such spectroscopy, establishes powerful tool investigations catalysis. The insights gained not only our transformation, but also provide framework probing similar Ni/Ir dual photocatalytic systems. 1 Introduction 2 Enantioselectivity Data Highlights Complex Mechanistic Scenario 3 Probing Predominant Pathway Experiments 4 MLR Modeling Understand Halogen Effect Enantioinduction 5 Proposed Prevalent Mechanism 6 Initiation Precatalyst 7 Conclusion

Language: Английский

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Advances in understanding comproportionation and disproportionation in nickel catalysis

Pure and Applied Chemistry, Journal Year: 2024, Volume and Issue: 96(3), P. 437 - 446

Published: March 1, 2024

Abstract Disproportionation and comproportionation reactions have become routinely proposed events in modern synthetic endevours that use nickel catalysts. This new found appreciation from practitioners the field for these electron transfer has largely stemmed our improved understanding of catalytic reactions. These studies shown evidence ability complexes to occupy odd even oxidation states which are critical dictating reactivity. Comproportionation disproportionation shuttle between essential formation either on-cycle or off-cycle species. review will cover fundamental reactions, provide information about their role catalysis.

Language: Английский

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