Well-defined palladium(0) complexes bearing N-heterocyclic carbene and phosphine moieties: efficient catalytic applications in the Mizoroki–Heck reaction and direct C–H functionalization

Lee, Jhen‐Yi; Shen, Jiun-Shian; Tzeng, Ru-Jiun; Lu, I-Chen; Lii, Jenn‐Huei; Hu, Ching‐Han; Lee, Hon Man

doi:10.1039/c6dt01323f

Cited by 47 publications

(28 citation statements)

References 63 publications

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“…The presence of ligand was essential as free PdCl 2 and Pd(OAc) 2 were much less effective (entries 8 and 9). Complex 4a was less active than the aforementioned Pd(L)(PCy 3 )(OAc) 2 , and our previously reported preformed palladium(0) complex featuring bidentate NHC and PPh 2 moieties which was capable of utilizing aryl chlorides as substrates. It should be noted that due to the unfavorable electronic repulsion between the lone pair on the N3 and the Pd―C(4) bond in the catalytic intermediate, the general reactivity trend of imidazole is that C5 is much more reactive than C4 position .…”

Section: Resultsmentioning

confidence: 82%

A tridentate CNO‐donor palladium(II) complex as efficient catalyst for direct C―H arylation: Application in preparation of imidazole‐based push–pull chromophores

Maitra

Kuo

et al. 2017

Applied Organom Chemis

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A series of imidazolium chlorides for the formation of tridentate CNO-donor palladium(II) complexes featuring N-heterocyclic carbene moieties have been developed from cheap and readily available starting materials with high yields.Their palladium complexes were prepared by reactions between the ligand precursors and PdCl 2 using K 2 CO 3 as base in pyridine with reasonable yields.These air-stable metal complexes were characterized using 1 H NMR and 13 C { 1 H} NMR spectroscopy and elemental analyses. Heteronuclear multiple bond correlation experiments were performed to identify key NMR signals of these compounds. The structures of two of the complexes were also established by single-crystal X-ray diffraction analysis. One of these complexes was successfully applied in the direct C-H functionalization reactions between heterocyclic compounds and aryl bromides, producing excellent yields of coupled products. The coupling reactions were scalable, allowing grams of coupled products to be obtained with a mere 2 mol% of Pd loading. The catalyst system developed allowed the large-scale preparation of several push-pull chromophores straightforwardly. Photophysical properties based on UV-visible and fluorescence spectroscopy for these chromophores were investigated. Deep blue photoluminescence with moderate quantum efficiency and twisted intramolecular charge transfer excited state were observed for these chromophores. Density functional theory (DFT) and time-dependent DFT calculations were performed to support the experimental results.

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Section: Resultsmentioning

confidence: 82%

A tridentate CNO‐donor palladium(II) complex as efficient catalyst for direct C―H arylation: Application in preparation of imidazole‐based push–pull chromophores

Maitra

Kuo

et al. 2017

Applied Organom Chemis

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“…A bidentate NHC-PPh 2 ligand has been utilized for the preparation of palladium(0) complexes to be used in Heck reactions [ 193 ]. The imidazolium salts 194 were prepared starting from N-substituted imidazoles which were first heated at 90 °C for 24 h in 1,2-dichloroethane to afford (β-chloroethyl)imidazolium chlorides.…”

Section: Synthesis and Applications Of Bidentate Ligands Bearing N-heterocyclic Carbenesmentioning

confidence: 99%

Recent Advances in Catalysis Involving Bidentate N-Heterocyclic Carbene Ligands

2021

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Since the discovery of persistent carbenes by the isolation of 1,3-di-l-adamantylimidazol-2-ylidene by Arduengo and coworkers, we witnessed a fast growth in the design and applications of this class of ligands and their metal complexes. Modular synthesis and ease of electronic and steric adjustability made this class of sigma donors highly popular among chemists. While the nature of the metal-carbon bond in transition metal complexes bearing N-heterocyclic carbenes (NHCs) is predominantly considered to be neutral sigma or dative bonds, the strength of the bond is highly dependent on the energy match between the highest occupied molecular orbital (HOMO) of the NHC ligand and that of the metal ion. Because of their versatility, the coordination chemistry of NHC ligands with was explored with almost all transition metal ions. Other than the transition metals, NHCs are also capable of establishing a chemical bond with the main group elements. The advances in the catalytic applications of the NHC ligands linked with a second tether are discussed. For clarity, more frequently targeted catalytic reactions are considered first. Carbon–carbon coupling reactions, transfer hydrogenation of alkenes and carbonyl compounds, ketone hydrosilylation, and chiral catalysis are among highly popular reactions. Areas where the efficacy of the NHC based catalytic systems were explored to a lesser extent include CO2 reduction, C-H borylation, alkyl amination, and hydroamination reactions. Furthermore, the synthesis and applications of transition metal complexes are covered.

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“…In contrast, the amide functional groups in 1 c offer the possibility of N H deprotonation and consequently bidentate chelation of the NHC ligand. Palladium complexes with donor‐functionalized NHC ligands had been used in direct C−H arylation reactions of heterocycles –…”

Section: Resultsmentioning

confidence: 99%

Dimetallic Palladium‐NHC Complexes: Synthesis, Characterization, and Catalytic Application for Direct C−H Arylation Reaction of Heteroaromatics with Aryl Chlorides

et al. 2019

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A series of dimetallic palladium(II)-NHC complexes comprised of 1,4-naphthalenyl or 9,10anthracenyl spacer sandwiched between two imidazole rings was successfully synthesized. These complexes were characterized by 1 H and 13 C{ 1 H} NMR spectroscopy and elemental analysis. The structures of two dimetallic palladium complexes and a related mononuclear palladium complex to be used for comparative studies were further characterized by X-ray diffraction. The dimetallic palladium complex with the 9,10anthracenyl linker was very efficient in catalyzing direct CÀ H arylation reactions of heteroaromatic compounds (imidazoles, imidazo[1,2-a]pyridine, and thioazole) with a broad range of aryl chlorides, employing a mild monopalladium loading of 1.5 mol%. It allows for the effective use of aryl chlorides to prepare arylated heterocycles, previously only accessible with the more reactive bromide counterparts. Importantly, the catalytic activity of the dimetallic precatalyst was found to be higher than that of an analogous mononuclear complex. Scheme 1. Synthesis of ligand precursors. Scheme 2. Synthesis of Dinuclear Palladium-NHC Complexes. Scheme 3. Synthesis of Mononuclear Palladium-NHC Complexes.

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Well-defined palladium(0) complexes bearing N-heterocyclic carbene and phosphine moieties: efficient catalytic applications in the Mizoroki–Heck reaction and direct C–H functionalization

Cited by 47 publications

References 63 publications

A tridentate CNO‐donor palladium(II) complex as efficient catalyst for direct C―H arylation: Application in preparation of imidazole‐based push–pull chromophores

A tridentate CNO‐donor palladium(II) complex as efficient catalyst for direct C―H arylation: Application in preparation of imidazole‐based push–pull chromophores

Recent Advances in Catalysis Involving Bidentate N-Heterocyclic Carbene Ligands

Dimetallic Palladium‐NHC Complexes: Synthesis, Characterization, and Catalytic Application for Direct C−H Arylation Reaction of Heteroaromatics with Aryl Chlorides

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