1,4,5,6-Tetrahydropyrimidinium Halides Ligands for Suzuki-Miyaura Cross-Coupling of Unactivated Aryl Chlorides (original) (raw)
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Arkivoc, 2007
Four bis(3,4,5,6-tetrahydropyrimidinium) chlorides (2a-d) have been prepared and characterized by conventional spectroscopic methods and elemental analyses. A highly effective, easy to handle and environmentally benign process for palladium mediated Suzuki cross-coupling was developed. The in situ prepared three-component system Pd(OAc) 2 / bis(3,4,5,6tetrahydropyrimidinium) chlorides (2a-d) and K 2 CO 3 catalyses quantitatively the Suzuki crosscoupling of deactivated aryl chlorides.
2021
Four novel N,N-bidentate triarylmethane-based ligands bearing β-pyridyl residues have been prepared and the catalytic activity of their in-situ generated palladium complexes were studied in the Suzuki–Miyaura cross-coupling reactions. Air and moisture stable 3,3'-((arylmethylene)bis(4-methoxy-3,1-phenylene))dipyridines L1-3 showed excellent activity in the Suzuki coupling reactions of aryl halides with aryl boronic acids under thermal and sonochemical reaction conditions. The described methodology provided good to high yields in short reaction times at ambient conditions. Moreover, it offered a straightforward way for Suzuki–Miyaura chemo- and homoselective cross-coupling of aryl halides with phenyl boronic acid. The structures of synthesized compounds were fully characterized by FT-IR, 1H-NMR, 13C-NMR, and elemental analyses. The coordination of palladium acetate to nitrogen sites of L1 was also studied using FTIR spectroscopy, EDX analysis and SEM observations. The in-situ gen...
Efficient salicylaldimine ligands for a palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction
Applied Organometallic Chemistry, 2012
A series of salicylaldimine ligands were designed to promote palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction. After a screening process, a ligand with a bulky 2,4‐di‐tert‐butyl substituent on the salicyaldehyde backbone and cyclohexylamine moiety was found to serve as a good combination for this reaction in aqueous solutions of DMF. The protocol demonstrated a significant advance in the efficiency of the cross‐coupling of aryl bromides and aryl chlorides with arylboronic acids to produce the desired biaryl products. Copyright © 2012 John Wiley & Sons, Ltd.
Journal of Organometallic Chemistry, 2012
The reaction of [PdCl 2 (PPh 3) 2 ] and substituted pyridoxal hydrazone ligands (H 2 L) in methanol under reflux afford a series of palladium ONO coordinated complexes with general formula [Pd(PPh 3)L] (where, L ¼ dianionic terdentate pyridoxal hydrazones). All the palladium complexes are air stable and fully characterized by elemental analysis, spectral and X-ray diffraction methods. In chloroform solution all the metal complexes exhibit characteristic metal to ligand charge transfer (MLCT) absorptions and ligand based transitions. Molecular structure of one of the complexes (3) has been determined by X-ray crystallography indicates that the pyridoxal hydrazone ligands are coordinated to the palladium as a terdentate O, N, O donor and a distorted square-planar geometry is observed around palladium(II) metal center. Further, palladium-catalyzed protocol for SuzukieMiyaura cross-coupling reactions by the complex (3) has been developed, enabling to obtain biaryl products in good to excellent conversions.
Polyhedron, 2017
The characterization of synthesized Schiff base ligands (L 1-L 5); (where L 1 = N-salicyliden-2,3-diaminocis-2-butenedinitrile, L 2 = 3-methoxy-N-salicyliden-2,3-diamino-cis-2-butenedinitrile, L 3 = 5-bromo-Nsalicyliden-2,3-diamino-cis-2-butenedinitrile, L 4 = 5-nitro-N-salicyliden-2,3-diamino-cis-2-butenedinitrile, and L 5 = 5-methoxy-N-salicyliden-2,3-diamino-cis-2-butenedinitrile) and their palladium complexes [PdL(PPh 3)] (L 1-L 5) were carried out by FT-IR, UV-vis, 1 H NMR, 13 C NMR and elemental analysis. The coordination geometry of [PdL 3 (PPh 3)] was determined by single crystal X-ray crystallography. In this structure the palladium center was in a partially distorted NNOP square planar coordination environment. The catalytic potential of the synthesized complexes was evaluated in Suzuki-Miyaura cross-coupling reaction by choosing different arylhalides and phenylboronic acid. The results showed that arylhalides with electron withdrawing substituents were more appropriate in this reaction. In all cases, the desired product of cross coupling Suzuki reaction was the major product. It is also worth to mention that the product of homo-coupling reaction was also observed as a minor product. In this regards, a blank reaction with just phenylboronic acid was performed and the results showed the occurrence of the homo-coupling product in a good yield.
—Palladium–benzimidazolium salt catalyst systems have been studied for the Suzuki coupling. A different substitutent effect has been uncovered with respect to nitrogen substituents in the benzimidazolium salts from the palladium–imidazolium salt analogs. A practical and highly active palladium catalyst system, PdCl 2 /N,N 0-dibenzylbenzimidazolium chloride 2, has been identified for the Suzuki coupling of aromatic halides with arylboronic acids. The coupling of a wide array of aromatic halides with arylboronic acids with the PdCl 2 –2 catalyst system gave good to excellent yields. The effective palladium loading could be as low as 0.0001 mol% and 0.01–0.1 mol% for iodide and bromide substrates, respectively. The coupling of unactivated aromatic chlorides with arylboronic acids also gave good results using Cs 2 CO 3 as base with a 2 mol% palladium loading. The electronic factors from aromatic halides exert a significant influence on the Suzuki coupling catalyzed by the PdCl 2 –2 system while the electronic effect from the arylboronic counterparts is negligible. The aromatic halides with modest steric hindrance could also couple smoothly with phenylboronic acids using the PdCl 2 –2 catalyst system.
Suzuki reaction of aryl chlorides using saturatedN-heterocarbene ligands
Heteroatom Chemistry, 2005
From readily available starting materials, six 1,3-dialkyl-imidazolinium bromides (2a-f) have been prepared and characterized by conventional spectroscopic methods and elemental analyses. The incorporation of saturated N-heterocyclic carbenes into palladium precatalysts gives high catalyst activity in the Suzuki coupling of deactivated aryl chloride substrates in aqueous media. The complexes were generated in the presence of Pd(OAc) 2 by in situ deprotonation of 2a-f.
Chemical Communications, 2008
In a glovebox, a 5 mL screwcap-vial fitted with a septum equipped with a magnetic stirring bar was charged with sodium methoxide (40.5 mg, 0.75 mmol), and the boronic acid (0.525 mmol). Outside the glovebox, the required amount of catalyst solution (catalyst loading 0.1 mol %) was injected through the septum, followed by addition of technical grade degassed ethanol (1 mL). The mixture was then stirred at room temperature unless otherwise indicated. After 15 min, the aryl halide (0.5 mmol) was injected, and the reaction was monitored by gas chromatography. When the reaction reached completion, or no further conversion was observed by gas chromatography, the solvent was removed under vacuum and the resulting solid was filtered on a pad of silica (using a hexanes/ethyl acetate mixture, depending on the polarity of the product). When necessary the product was purified by flash chromatography on silica gel. For reactions carried out under aerobic conditions, all solids were weighted in air. The solvents were dried over molecular sieves and all liquids were injected in vials opened to air. 4-methylbiphenyl 4 (Table 1): The procedure afforded, after flash chromatography on silica gel (hexanes), 78.2 mg (93%) of the title compound.