N,N′-Mono substituted acyclic thioureas: efficient ligands for the palladium catalyzed Heck reaction of deactivated aryl bromides

Srinivas, K.; Parvathaneni, Sai Prathima; Mandapati, Mohan Rao

doi:10.1016/j.tetlet.2014.09.053

Cited by 10 publications

(2 citation statements)

References 34 publications

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“…The multidentate phosphine ligand promoted Sonogashira coupling reactions in water under 1-500 ppm Pd (Scheme 1c) [8,9]. Interestingly, N-phenylurea, thiourea, and amide efficiently accelerated the 1-100 ppm, Pd-catalyzed Suzuki reaction (Scheme 1d) [10]. Although these new ligands have a significant role in the trace palladium-catalyzed coupling reactions, most phosphine ligands are expensive, highly toxic, and sensitive to air and water [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

α, β-Alkynone Accelerated PPM Level Pd-Catalyzed Sonogashira Coupling Reaction

Guo

Wei

Yang³

et al. 2020

Catalysts

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In the palladium-catalyzed C−C coupling reaction, electron-rich phosphine ligands and a catalytic amount of catalyst loading are required in most cases. Herein, a bench-stable, easily modified and less toxic alkynone was utilized in palladium-catalyzed Sonogashira coupling to replace conventional phosphine ligands. With 1-(4-methoxyphenyl)-3-phenyl-2-yn-1-one (L2) as the ligand, catalyst loading was reduced to 5-10 ppm. In this newly developed catalytic system, a variety of (hetero)arene iodines and alkynes could be tolerated, resulting in good yields of the corresponding cross-coupling products.

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Section: Introductionmentioning

confidence: 99%

α, β-Alkynone Accelerated PPM Level Pd-Catalyzed Sonogashira Coupling Reaction

Guo

Wei

Yang³

et al. 2020

Catalysts

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“…The palladium-catalyzed cross-coupling reactions of aryl halides with arylboronic acids (Suzuki–Miyaura reactions) or alkynes (Sonogashira reactions) have provided a powerful methodology for constructing C–C bonds. − Phosphine ligands − are generally required to stabilize the active catalytic palladium intermediates. However, such ligands suffer from disadvantages of cost, toxicity, sensitivity to air/moisture, or difficulty of removal from the organic products, which restricts their applications in synthesis. , Among the phosphine-free ligands, N-heterocyclic carbenes (NHCs) − and nitrogen-donors ligands − are arguably the most useful, but thiols and thioether-based SS, NS, SCS, , NNS, NCS, , NSN , bidentate and tridentate ligands are also emerging as viable alternatives. , One complication with sulfur-based ligands, however, is that Pd catalysts can mediate C–S bond cleavage. − Nevertheless, thiourea derivatives have been extensively used as versatile ligands for many Pd-catalyzed organic reactions. − Imidazole-2-thiones have also attracted much attention, because their steric and electronic properties can be tuned by varying groups on the imidazolyl ring. Moreover, the CS double bond in these ligands displays high thermal and chemical stability.…”

Section: Introductionmentioning

confidence: 99%

Palladium(II) Chloride Complexes of N,N′-Disubstituted Imidazole-2-thiones: Syntheses, Structures, and Catalytic Performances in Suzuki–Miyaura and Sonogashira Coupling Reactions

Zhang

et al. 2017

Inorg. Chem.

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Reactions of PdCl with 2 equiv of N,N'-disubstituted-imidazole-2-thiones RRCNS (R = R = Me (1a), Pr (1b), Cy (1c), CMeH (1d); R = Me, R = Ph (1e)) under the different conditions afford five mononuclear complexes trans-[(RRCNS)PdCl] (R = R = Me (2a), Pr (2b), Cy (2c), CMeH (2d); R = Me, R = Ph (2e)) and five binuclear Pd(II) complexes [(PdCl){μ-(RRCNS)}] (R = R = Me (3a), Pr (3b), Cy (3c), CMeH (3d); R = Me, R = Ph (3e)), respectively. Complexes 2a-2e are easily converted into the corresponding 3a-3e by adding equimolar PdCl in refluxing MeOH, while the reverse reaction is achieved at room temperature by addition of 2 equiv of 1a-1e. In 2b, 2d, and 2e, each Pd(II) holds a distorted square planar geometry completed by two trans Cl atoms and two trans S atoms. Complexes 3a-3e have a dimeric [PdS] structure in which two {PdCl} units are interlinked by two N,N'-disubstituted-imidazole-2-thiones. Each Pd(II) adopts a distorted square planar geometry accomplished by two cis Cl atoms and two cis bridging S atoms. Among them, complex 3d has the two largest CMeH groups on the 2 and 5 positions of imidazole-2-thione, the longest Pd-μ-S bond, the largest S-Pd-S angle, and displays the highest catalytic activity toward Suzuki-Miyaura and copper-free Sonogashira cross-coupling reactions, which are confirmed by density functional theory calculations. The results provide an interesting insight into the introduction of various substituent groups into the periphery ligands of coordination complex-based catalysts, which could tune their geometric structures to acquire the best catalytic activity toward organic reactions.

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