Azo-azomethine based palladium(II) complexes as catalysts for the Suzuki-Miyaura cross-coupling reaction (original) (raw)
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Modified zeolite immobilized palladium for ligand-free Suzuki–Miyaura cross-coupling reaction
Journal of Organometallic Chemistry, 2013
A palladium-based catalyst supported on modified ZSM-5 was successfully prepared by a facile procedure. The prepared heterogeneous catalyst Pd@desilicated ZSM-5 showed an excellent catalytic activity at very low Pd loading (0.02 mol%) for the ligand-free SuzukieMiyaura coupling reactions of various aryl bromides affording excellent yields of the products. The prepared catalyst presents good recyclability, over four catalytic cycles.
Tetrahedron Letters, 2010
A new polystyrene anchored Pd(II) azo complex has been synthesized and characterized. The present Pd(II) azo complex behaves as a very efficient heterogeneous catalyst in the Suzuki coupling and Sonogashira coupling reaction in water medium. Aryl halides, coupled with phenylboronic acids (Suzuki-Miyaura reaction) or terminal alkyne (Sonogashira reaction), smoothly afford the corresponding crosscoupling products in excellent yields (83-100% yield for Suzuki reaction and 68-96% yield for Sonogashira reaction of aryl halides) under phosphine-free reaction conditions in the presence of polystyrene anchored Pd(II) azo complex catalyst in water medium. Furthermore, the catalyst has shown good thermal stability and recyclability. This polymer-supported Pd(II) catalyst could be easily recovered by simple filtration of the reaction mixture and reused for more than six consecutive trials without a significant loss of its catalytic activity.
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-Catalyzed Suzuki–Miyaura Reaction Using Saturated N -Heterocarbene Ligands
Catalysis Letters, 2004
The incorporation of saturated N-heterocyclic carbenes into palladium pre-catalysts give high catalyst activity in the Suzuki coupling of deactivated aryl chloride substrates. The complexes were generated in the presence of Pd(OAc)2 by in situ deprotonation of bis(imidazolinium) bromides LHX (3) which were characterized by conventional spectroscopic methods and elemental analyses.
Journal of Organometallic Chemistry, 2014
A series of dichloropalladium(II) complexes (Pd1ePd4ox) based on derivatives of the hemilabile 2-(1Himidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands were synthesized and characterized. The ligands were designed to introduce a variety of electronic and structural features and crystal structures of Pd1, Pd1Me, Pd3, and Pd3Me were determined. Pd1 and Pd1Me both crystallize in the monoclinic space group C2/c. Pd3 crystallizes in the monoclinic space group P2 1 /c while Pd3Me crystallizes in the orthorhombic space group P2 1 2 1 2 1. All complexes were utilized as pre-catalysts in a comparative study to probe relevant features of the palladium active species during high temperature SuzukieMiyaura crosscoupling catalysis. Relatively higher catalytic activities were obtained for complexes bearing the bidentate ligands that possess weaker azole donor arms. Results obtained suggest that ligand dissociation steps may be important for generating active species with high efficiency. In particular, the observed ligand effects in the investigated series indicate that higher catalyst efficiencies were observed with complexes for which the coordination of the ligand at the palladium center could readily be converted into a monodentate mode.
TURKISH JOURNAL OF CHEMISTRY, 2015
A new series of N, N-type 2-(2'-pyridyl)benzimidazole ligands (2A 1 , 2A 2 , 3B 1 , 3B 2 , 3B 3 , and 4C 1) and their Pd(II) complexes (5A 1 , 5A 2 , 6B 1 , 6B 2 , 6B 3 , and 7C 1) were prepared and characterized by conventional spectroscopic methods and elemental analyses. The incorporation of N-coordinated benzimidazole complexes of palladium gave high catalytic activity in the Suzuki-Miyaura coupling of aryl halides substrates. After determining the best active catalyst as 5A 1 , bearing the mesityl substituent on the benzimidazole ring with the Pd(II) ion, optimization studies were carried out via changing the substrate, base, time, atmosphere, and the effect of water. The DMF:H 2 O (4/1) and Cs 2 CO 3 as base were found to be critical for the efficiency of the reaction yield (100%).
Advanced Synthesis & Catalysis, 2006
A wide array of forms of palladium has been utilized as precatalysts for Heck and Suzuki coupling reactions over the last 15 years. Historically, nearly every form of palladium used has been described as the active catalytic species. However, recent research has begun to shed light on the in situ transformations that many palladium precatalysts undergo during and before the catalytic reaction, and there are now many suggestions in the literature that narrow the scope of types of palladium that may be considered true "catalysts" in these coupling reactions. In this work, for each type of precatalyst, the recent literature is summarized and the type(s) of palladium that are proposed to be truly active are enumerated. All forms of palladium, including discrete soluble palladium complexes, solid-supported metal ligand complexes, supported palladium nano-and macroparticles, soluble palladium nanoparticles, soluble ligandfree palladium, and palladium-exchanged oxides are considered and reviewed here. A considerable focus is placed on solid precatalysts and on evidence for and against catalysis by solid surfaces vs. soluble species when starting with various precatalysts. The review closes with a critical overview of various control experiments or tests that have been used by authors to assess the homogeneity or heterogeneity of catalyst systems.
Bis(pyrazolyl)palladium(II) complexes as catalysts for Mizoroki–Heck cross-coupling reactions
Polyhedron, 2019
Recent progress in carbon-carbon cross-coupling reactions has resulted in the discovery of highly active catalysts for carrying out such transformations. However, due to the wide array of applications of the products from cross-coupling reactions, there is the need to design suitable catalysts that permit the practical and economical synthesis of the cross-coupled products. Palladium complexes with bulky and electron-donating ligands have served as excellent (pre)catalysts for the Mizoroki-Heck cross-coupling reaction. By using bulky pyrazole-based ligands, we have prepared palladium(II) complexes with controlled steric and electronic properties of the metal centre. We have used these bulky bis(pyrazolyl)palladium(II) complexes as (pre)catalysts for the Mizoroki-Heck cross-coupling reaction. The (pre)catalysts displayed high activity and selectivity, giving high catalytic conversions at a low (pre)catalyst loading and short reaction times. A mercury poisoning test confirmed that the (pre)catalysts promoted the Mizoroki-Heck cross-coupling homogenously and do not decompose into palladium black during the reactions. The catalytic systems were also tolerant to the presence of functional groups, such as 4-CF3, 4-CH3, 4-CO2Me and 4-CO2Et, on the alkene substrates.