Ni‐Catalyzed Photochemical C−N Coupling of Amides with (Hetero)aryl Chlorides

Song, Geyang; Li, Qi; Nong, Ding-Zhan; Song, Jiuzhou; Li, Gang; Wang, Chao; Xiao, Jianliang; Xue, Dong

doi:10.1002/chem.202300458

Cited by 19 publications

(8 citation statements)

References 64 publications

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“…The axial g tensor values are overall consistent with a single unpaired electron in the Ni(I) 3 d ( x 2 – y 2 ) orbital. The EPR spectra and g values of compounds 1-Cl/Br and 3-Cl are congruent with previous reports for Ni(I) halide species with aromatic ligand backbones (e.g., phenanthroline, bipyridine, and bis(pyrazolyl)pyridines). ,,− The 14 N hyperfine values employed in the 3-Cl simulation are of comparable magnitude to those previously reported for Ni(I)-neocuproine complexes (0, 50, and 170 MHz) . Sufficiently high concentration samples of 2-Cl were precluded due to a precipitation (dimerization) pathway (vide infra, Section ); as such, no EPR signal could be detected.…”

Section: Results and Analysissupporting

confidence: 88%

“…The intermediate peak at ∼310 mT in 1-Cl/Br/I is likely attributable to THF solvent coordination (see Supporting Information Section S2.7), as it does not appear in previous spectra recorded in toluene but does appear in toluene−THF solvent mixtures and in neat 2-MeTHF. 42,43 These published data share excellent agreement with the spectra collected and presented in Figure 2C. Importantly, the relative intensities of the g z and intermediate peaks remain approximately constant with variations in photolysis time, indicating that there is not a second Ni(I) species with a distinct kinetic profile (Figures S33−S35).…”

Section: Including Figures S6−s10)mentioning

confidence: 85%

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

et al. 2023

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We report the facile photochemical generation of a library of Ni(I)−bpy halide complexes (Ni(I)( R bpy)X (R = t-Bu, H, MeOOC; X = Cl, Br, I) and benchmark their relative reactivity toward competitive oxidative addition and off-cycle dimerization pathways. Structure−function relationships between the ligand set and reactivity are developed, with particular emphasis on rationalizing previously uncharacterized ligand-controlled reactivity toward high energy and challenging C(sp 2 )−Cl bonds. Through a dual Hammett and computational analysis, the mechanism of the formal oxidative addition is found to proceed through an S N Ar-type pathway, consisting of a nucleophilic two-electron transfer between the Ni(I) 3d(z 2 ) orbital and the C aryl −Cl σ* orbital, which contrasts the mechanism previously observed for activation of weaker C(sp 2 )−Br/I bonds. The bpy substituent provides a strong influence on reactivity, ultimately determining whether oxidative addition or dimerization even occurs. Here, we elucidate the origin of this substituent influence as arising from perturbations to the effective nuclear charge (Z eff ) of the Ni(I) center. Electron donation to the metal decreases Z eff , which leads to a significant destabilization of the entire 3d orbital manifold. Decreasing the 3d(z 2 ) electron binding energies leads to a powerful two-electron donor to activate strong C(sp 2 )−Cl bonds. These changes also prove to have an analogous effect on dimerization, with decreases in Z eff leading to more rapid dimerization. Ligand-induced modulation of Z eff and the 3d(z 2 ) orbital energy is thus a tunable target by which the reactivity of Ni(I) complexes can be altered, providing a direct route to stimulate reactivity with even stronger C−X bonds and potentially unveiling new ways to accomplish Ni-mediated photocatalytic cycles.

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Section: Results and Analysissupporting

confidence: 88%

Section: Including Figures S6−s10)mentioning

confidence: 85%

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

et al. 2023

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“…As is seen in Figure 2, A, the C−N couping was only sluggish in the absence of d ‐Mebpy. UV/Vis and HRMS measurements (see Supporting Information, section 8.2, 8.4) suggest that d ‐Mebpy reacts with the Werner salt to form a d ‐Mebpy‐ligated complex, [Ni( d ‐Mebpy)Cl 2 ], which is known to be active in catalyzing C−N coupling [10e] . Thus, mixing the ligand (1.0 equiv) with [Ni(NH 3 ) 6 ]Cl 2 in DMSO/THF afforded a green solution under light excitation, the UV/Vis absorption of which is almost identical to that of [Ni( d ‐Mebpy)Cl 2 ] (Figure 2, C, see Supporting Information, section 8.4) [11] .…”

Section: Resultsmentioning

confidence: 99%

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

Song,

et al. 2023

Angew Chem Int Ed

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Cheap, stable and easy‐to‐handle Werner ammine salts have been known for more than a century; but they have been rarely used in organic synthesis. Herein, we report that the Werner hexammine complex [Ni(NH₃)₆]Cl₂ can be used as both a nitrogen and a catalytic nickel source that allow for the efficient amination of aryl chlorides in the presence of a catalytic amount of bipyridine ligand under the irradiation of 390‐395 nm light without the need of any additional catalysts. More than 80 aryl chlorides, including more than 20 drug molecules, were aminated, demonstrating the practicality and generality of this method in synthetic chemistry. A slow NH3 release mechanism is in operation, obviating the problem of catalyst poisoning. Still interestingly, we show that the Werner salt can be easily recovered and reused, solving the problem of easy deactivation and difficult recovery of transition metal nickel catalysts. The protocol thus provides an efficient new strategy for the synthesis of primary aryl amines.

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“…The authors have cited additional references within the Supporting Information. [12][13][14][15][16][17][18]…”

Section: Supporting Informationmentioning

confidence: 99%

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

Bradley,

McManus,

Yam

et al. 2023

Angewandte Chemie

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

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Ni‐Catalyzed Photochemical C−N Coupling of Amides with (Hetero)aryl Chlorides

Cited by 19 publications

References 64 publications

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

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

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

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

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Ni‐Catalyzed Photochemical C−N Coupling of Amides with (Hetero)aryl Chlorides

Cited by 19 publications

References 64 publications

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

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

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

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

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Product

Resources

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

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