Versatile Palladium-Catalyzed Approach to Acyl Fluorides and Carbonylations by Combining Visible Light- and Ligand-Driven Operations

Liu, Yi; Zhou, Cuihan; Jiang, Meijing; Arndtsen, Bruce A.

doi:10.1021/jacs.2c01951

Cited by 44 publications

(41 citation statements)

References 52 publications

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“…Based on the mechanistic experiments presented (Schemes and ), we postulate that the entire C–I bond forming process is reversible through a single-electron pathway. Furthermore, as indicated by the stoichiometric experiments, and the reports from Arndsten , this phenomenon of C–X bond formation via irradiation of Pd(II)–X complexes with blue light may be more general than anticipated.…”

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confidence: 99%

Pd(0)/Blue Light Promoted Carboiodination Reaction – Evidence for Reversible C–I Bond Formation via a Radical Pathway

et al. 2022

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A Pd(0)/blue light catalyzed carboiodination reaction is reported. A simple, air-stable catalytic system, utilizing [Pd(allyl)Cl] 2 and DPEPhos, generated a variety of iodinated hetero-and carbocycles including oxindoles, dihydrobenzofurans, indolines, a chromane, and a tetrahydronaphthalene. This protocol was tolerant of sensitive functional groups including free carboxylic acids, phenols, and anilines, as well as pyridines, while delivering products in up to 94% yield. Support for a reversible C−I bond formation via a single electron mechanism was obtained using a deuterium labeled substrate and a stoichiometric neopentylpalladium species.T ransition-metal catalyzed halogenation protocols have often hinged on gaining a deeper understanding of the reversibility of carbon−halogen bond forming events. One powerful synthetic strategy that implements reversible C−X bond formation is the palladium-catalyzed carboiodination reaction, wherein halogenated heterocycles can be built from the intramolecular transfer of a C(sp 2 )−X group across a tethered π-system. 1−4 Traditionally, palladium catalyzed carboiodination reactions involve a 2-electron mechanistic cycle and are initiated by a ground-state Pd(0) catalyst undergoing an oxidative addition with an aryl halide. 1,2,4 Recently, the use of blue light in conjunction with palladium catalysis has offered a convenient route to access excited-state palladium species. 5−10 Unlike their thermal counterparts, photochemical reactions involving excited-state Pd(0) are typically thought to involve tandem palladium/radical intermediates. These reactions can mimic the reactivity of ground state palladium species, via a single electron mechanism in domino reactions. 6,8,10−13 Though the presence of radical intermediates has been well established, 5,6,14 a mechanism involving both discrete Pd(II) intermediates and alkyl radical/Pd(I) species has not been broadly explored.Thermally initiated carboiodination reactions typically employ a palladium catalyst bearing bulky electron-rich phosphines, or a nickel catalyst and a PPh 3 , P(OR) 3 or an N,N-ligand. 1,15−20 These reaction mechanism initiate via an oxidative addition to the C−I bond, followed by a migratory insertion across the π-system, and terminate with a ligandmediated 3-center 2-electron, 18 or an H-bonding initiated S N 2type reductive elimination. 21 The most successful conditions for the palladium carboiodination reactions utilize high temperatures and QPhos or t-Bu 3 P, costly and air-sensitive bulky phosphines (Scheme 1a). Often times, bulky 3°-amine

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confidence: 99%

Pd(0)/Blue Light Promoted Carboiodination Reaction – Evidence for Reversible C–I Bond Formation via a Radical Pathway

et al. 2022

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“…Two years later, the same authors provided an extension of this methodology to synthesize acyl fluorides from aryl, heteroaryl, alkyl, and functionalized organic halides (Scheme 25 B). 61 The combination of visible light and palladium catalysis offers a versatile platform for the synthesis of acyl fluorides from readily available organic halides, carbon monoxide, and fluoride.…”

Section: Generation Of Acyl Radicalsmentioning

confidence: 99%

Light-Driven Palladium-Radical Hybrid Species: Mechanistic Aspects and Recent Examples

Jardim¹,

Paixão²,

Ferreira³

et al. 2022

Synthesis

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Visible light-induced Pd mediated reactions have become a novel and promising field in organic synthesis. This photocatalytic arsenal presents complementary features towards traditional Pd-chemistry, allowing the achievement of new and unique reactivities by generation of versatile Pd-radical hybrid species. These putative intermediates can be produced by direct excitation of Pd complexes, together with organic radical precursors. This review aims at describing recent advances regarding the combination of Pd-based photocatalytic manifolds and radical generation in the functionalization of important motifs in synthetic chemistry, encompassing detailed mechanism descriptions and relevant examples.

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“…Within this single catalyst framework, the light energy can be utilized more efficiently than in the dual-catalyst system due to the intramolecular electron/energy transfer process. Although there have been increasing numbers of reports on visible-light-induced transition-metal catalysis using conventional ligands and complexes, , this concept is still in its infancy, and there is a high demand for rationally designed visible-light-responsive ligands applicable to various metals …”

Section: Introductionmentioning

confidence: 99%

Shining Visible Light on Reductive Elimination: Acridine–Pd-Catalyzed Cross-Coupling of Aryl Halides with Carboxylic Acids

2022

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Despite the recent tremendous progress on transition-metal/photoredox dual catalysis in organic synthesis, single transition-metal catalysis under visible-light irradiation, which can utilize light energy more efficiently, is still underdeveloped. Herein, we report the design of photosensitizing phosphinoacridine bidentate ligands for visible-light-induced transition-metal catalysis, expecting that the electron-accepting acridine moiety would create a highly reactive electron-deficient metal center toward reductive elimination via metal-to-ligand charge transfer (MLCT). Using these ligands, we have achieved a palladium-catalyzed cross-coupling reaction of aryl halides with carboxylic acids under visible-light irradiation. Electronic tuning of the phosphinoacridine ligands not only enabled the use of a variety of aryl halides as the coupling partner, including less reactive aryl chlorides, under blue light irradiation, but also realized the employment of lower-energy green and red light for the cross-coupling. Experimental mechanistic studies have proved that the reductive elimination of aryl esters is induced by photoirradiation of phosphinoacridine-ligated arylpalladium(II) carboxylate complexes. The theoretical calculation suggests that the reductive elimination in the excited state is promoted by decreasing the electron density of the Pd center through photoinduced intramolecular electron transfer, i.e., MLCT, in the transition state owing to the electron-deficient acridine scaffold. This is a very rare example of photoinduced reductive elimination on palladium(II) complexes.

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Versatile Palladium-Catalyzed Approach to Acyl Fluorides and Carbonylations by Combining Visible Light- and Ligand-Driven Operations

Cited by 44 publications

References 52 publications

Pd(0)/Blue Light Promoted Carboiodination Reaction – Evidence for Reversible C–I Bond Formation via a Radical Pathway

Pd(0)/Blue Light Promoted Carboiodination Reaction – Evidence for Reversible C–I Bond Formation via a Radical Pathway

Light-Driven Palladium-Radical Hybrid Species: Mechanistic Aspects and Recent Examples

Shining Visible Light on Reductive Elimination: Acridine–Pd-Catalyzed Cross-Coupling of Aryl Halides with Carboxylic Acids

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