Carbene Palladium Complexes Research Articles

Two-Step Mechanochemical Synthesis of Carbene Complexes of Palladium(II) and Platinum(II)

A mechanochemical strategy for the synthesis of N-heterocyclic carbene complexes is described, in which 1,3-dibenzylimidazole complexes of palladium and platinum are produced in a two-step process by grinding together the reactants with a mortar and pestle. Crystallographic characterization reveals that unlike the solution syntheses, which produce a mixture of products, the solid-state reactions occur under topochemical conditions affording isomerically and polymorphically pure products.

Synthesis and characterization of N-heterocyclic carbene–PdCl2–1H-benzotriazole complexes and their catalytic activities toward Mizoroki–Heck and Sonogashira reactions

Four heteroleptic palladium complexes containing both N-heterocyclic carbenes and 1H-benzotriazole were synthesized and characterized. The solid-state structures show mononuclear carbene palladium complexes with each palladium coordinated by an NHC, the 3-position nitrogen of 1H-benzotriazole and two trans chlorides. The catalytic performance of the complexes for Mizoroki–Heck and Sonogashira reactions were further investigated. The results reveal that the complexes show high catalytic activities for coupling of aryl bromides with alkenes and alkynes.

Effect on orthometallation of NHC palladium complexes toward the catalytic activity studies in Suzuki coupling reaction.

Herein, we report an approach to improve catalytic activity for cross-coupling reactions. N-Heterocyclic carbene (NHC) palladium complexes bearing a nitrogen-based ligand without orthometallation complexes show remarkable activities in Suzuki coupling reaction than orthometallation. Aryl chlorides examples employed in air and ambient temperature in Suzuki coupling reaction to reach completion within few minutes.

Synthesis, characterization, crystal structure and in vitro anticancer potentials of mono and bimetallic palladium(II)–N–heterocyclic carbene complexes

N–heterocyclic carbene (NHC) complexes of palladium(II) are generally active as catalysts toward various coupling reactions, while their pharmacological efficiencies are seldom explored. A new series of palladium(II) complexes of both, functionalized and non–functionalized NHCs that were active against the human colon cancer (HCT116) cells are reported. Complexes were prepared by the technique of transmetallation using palladium source and in situ prepared silver(I)–NHC complexes in acetonitrile, and all complexes are characterized using spectroscopic and analytical tools. Additionally, the structure of palladium complex 9 was elucidated using single crystal X–ray diffraction method. In vitro anticancer studies revealed that the palladium complexes, 9 and 10, having xylyl–spacers significantly inhibited the HCT116 cell growth, exhibiting IC50 values in low micromolar range in MTT assay.

Abnormal-NHC Palladium(II) Complexes: Rational Synthesis, Structural Elucidation, and Catalytic Activity

Reaction of a C2-arylated imidazolium iodide (IPrPh)I (1) (IPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazolium) with PdCl2 in the presence of Ag2O affords abnormal N-heterocyclic carbene (aNHC) palladium complexes (aIPrPh)PdCl2 (2) and (aIPrPh)2PdCl2 (3) (aIPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazol-4-ylidene). Treatment of 2 with a pyridine gives Pd-PEPPSI-type complexes (aIPrPh)PdCl2(L) (L = pyridine (py), 5; L = 3-chloropyridine (3Cl-py), 6). Compounds 5 and 6 are also accessible by a one-pot reaction of 1, PdCl2, and Ag2O in a pyridine solvent. While the use of a conventional base K2CO3 leads to the formation of mixed halide complexes (aIPrPh)Pd(Cl)I(L) (7, L = py; 8, L = 3Cl-py), iodide derivatives (aIPrPh)PdI2(L) (9, L = py; 10, L = 3Cl-py) can be selectively prepared with addition of an excess of KI to the reaction mixture. Albeit in a low yield, a putative transmetalation agent {(aIPrPh)2Ag}AgI2 (4) has been isolated and characterized. Compounds 2–10 are air stable crystalline...

ChemInform Abstract: Supporting Ligand‐Assisted N‐Heterocyclic Carbene Palladium Complexes: Characterization, Computation, and Catalytic Activity in Suzuki—Miyaura Cross Coupling Between Aryl and Heteroaromatic Chlorides and Various Boronic Acids.

AbstractThis method uses catalyst loadings as low as 0.005 mol%.

ChemInform Abstract: Pd(0)‐Catalyzed Cross‐Coupling of Allyl Halides with α‐Diazocarbonyl Compounds or N‐Mesylhydrazones: Synthesis of 1,3‐Diene Compounds.

With palladium catalysis, allyl bromides or chlorides react with α-diazocarbonyl compounds or N-mesylhydrazones to afford 1,3-diene derivatives. The reaction represents a novel and efficient method for the synthesis of 1,3-butadiene derivatives. Mechanistically, the reaction is proposed to follow a pathway involving the formation of a π-allylic palladium carbene complex and subsequent migratory insertion.

Synthesis and crystal structures of palladium(II) complexes of bis-(N-heterocyclic carbenes) on a calix[4]arene platform

A series of calix[4]arene supported N-heterocyclic carbene palladium complexes were successfully prepared and characterised. Their X-ray crystal structures were obtained and are discussed. Notably, the dimeric compound b[5-(3-N-4,5-diphenylimidazol-2-yliden-1-yl)-25,26,27,28-tetrapropyloxy calix[4]arene] palladium(II) dibromide (cone) showed pseudo-polymorphism.

Piperazine‐ and DABCO‐bridged dinuclear N‐heterocyclic carbene palladium complexes: synthesis, structure and application to Hiyama coupling reaction

Four dinuclear N‐heterocyclic carbene (NHC) palladium complexes were prepared by reaction of imidazolinium salts, PdCl2 and bridging ligands (piperazine and DABCO) in one pot or by direct cleavage of the chloro‐bridged dimeric compounds [Pd(μ‐Cl)(Cl)(NHC)]2 with bridging ligands. All of the complexes were fully characterized using 1H NMR, 13C NMR, high‐resolution mass and infrared spectroscopies, elemental analysis and single‐crystal X‐ray diffraction. The catalytic activities of the obtained palladium catalysts towards Hiyama coupling of aryl chlorides with phenyltrimethoxysilane were investigated and the results showed that the dinuclear palladium complexes were considerably active for the coupling reaction. Copyright © 2016 John Wiley & Sons, Ltd.

ChemInform Abstract: Picolyl Functionalized Chelating N‐Heterocyclic Carbene Palladium Complexes: Synthesis and Catalytic Activity Towards Suzuki Cross‐Coupling in Water.

AbstractThe title NHC‐catalyst efficiently catalyzes the Suzuki cross‐coupling reaction in water in the presence of K3PO4 as base.

ChemInform Abstract: A New N—Heterocyclic Carbene Palladium Complex Immobilized on Nano Silica: An Efficient and Recyclable Catalyst for Suzuki—Miyaura C—C Coupling Reaction.

AbstractThe catalyst can be reused several times without loss of activity.

Reactivity studies of pincer bis-protic N-heterocyclic carbene complexes of platinum and palladium under basic conditions.

Bis-protic N-heterocyclic carbene complexes of platinum and palladium (4) yield dimeric structures 6 when treated with sodium tert-butoxide in CH2Cl2. The use of a more polar solvent (THF) and a strong base (LiN(iPr)2) gave the lithium chloride adducts monobasic complex 7 or analogous dibasic complex 8.

Bis-N-heterocyclic carbene silver(I) and palladium(II) complexes: Efficient antiproliferative agents against breast cancer cells

ABSTRACTA new Pd(II)-N-heterocyclic carbene (NHC) complex 2 was derived from a binuclear Ag(I)-NHC complex 1. 1H NMR spectra of complexes showed uniquely different characteristic behavior of bridging methylene protons than compared with the ligand. X-ray crystallography showed that palladium at the center of bis-NHC units in 2 was found in square-planar geometry. Ligand and complexes were tested against breast cancer cells (MCF-7). The ligand did not show considerable antiproliferative activity (IC50 181.0 ± 3.0 µM) whereas complexes showed significant activity (1: 0.5 ± 0.1 μM; 2: 2.5 ± 0.2 μM) compared with the standard drug, tamoxifen (2.4 ± 0.2 μM).

Catalytic activity of chelating N-heterocyclic carbene palladium complexes towards selective phosphorylation of coumarins

The catalytic activity of a series of heteroaryl coordinated chelating N-heterocyclic carbene (NHC) palladium complexes bearing different N-substituents, NHC backbones and chelating rings towards the phosphorylation of coumarins, and the relationship between the activity and the structure are presented. The results showed that the chelating NHC palladium complex Ia–b bearing the most σ-donating backbone and a more rigid five-membered chelating ring showed the highest efficiency. Using AgNO3 as oxidant, a wide range of coumarins reacted with different dialkyl phosphite or diphenylphosphine oxide smoothly in CH3CN, producing the target product in moderate to high yields.

Vinylic Addition Polynorbornene as Support for N‐Heterocyclic Carbene Palladium Complexes: Use as Reservoir of Active Homogeneous Catalytic Species in C−C Cross‐Coupling Reactions

AbstractA vinylic addition polynorbornene (VA‐PNB) functionalized with imidazolium groups can be used to synthesize a well‐defined supported palladium carbene complex. This complex is a suitable precatalyst for Suzuki and Negishi cross‐coupling reactions, and it can be reused. A close look at how the catalysis works reveals that palladium aggregates form on the polymer surface after the first catalytic reaction. However, they are not easily washed out and serve as a source of small amounts of homogeneous palladium active species (about 0.01% mol), which are responsible for the catalysis. The recovered polymer can be reused several times although increased induction and reaction times are observed in consecutive uses from one run to the next. The reaction was followed up by in situ IR spectroscopy by using the ν(C−Br) absorption band of the electrophile, so there is no need for an additional functional group to apply this technique.

Magnetic iron oxide nanoparticles–N‐heterocyclic carbene–palladium(II): a new, efficient and robust recyclable catalyst for Mizoroki–Heck and Suzuki–Miyaura coupling reactions

A new and efficient nanoparticle–N‐heterocyclic carbene–palladium complex was synthesized and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy‐dispersive X‐ray analysis, X‐ray diffraction, transmission electron microscopy, elemental analysis, inductively coupled plasma analysis and vibrating sample magnetometry. This catalytic system was found to be a highly active catalyst in the Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions. These reactions were best performed in dimethylformamide and water, respectively, in the presence of only 0.054 mol% of palladium under mild conditions. Moreover, the catalyst could be recovered easily and reused at least ten times without any considerable loss of its catalytic activity. Copyright © 2016 John Wiley & Sons, Ltd.

Picolyl Functionalised ChelatingN-Heterocyclic Carbene Palladium Complexes: Synthesis and Catalytic Activity towards Suzuki Cross-coupling in Water

Picolyl Functionalised Chelating<i>N</i>-Heterocyclic Carbene Palladium Complexes: Synthesis and Catalytic Activity towards Suzuki Cross-coupling in Water

Supporting ligand-assisted N-heterocyclic carbene palladium complexes: characterization, computation, and catalytic activity in Suzuki–Miyaura cross coupling between aryl and heteroaromatic chlorides and various boronic acids

A new series of imine–Pd–(N-heterocyclic carbene) complexes have been developed as efficient catalysts for Pd-catalyzed Suzuki–Miyaura coupling reaction. Based on the performance of supporting ligands, correlation of structure and catalytic activity has been demonstrated via experimental and computational modeling. A broad reaction scope of aryl and heteroaromatic chlorides could proceed at extremely low catalyst loading (minimum 0.005mol%).

Solvent‐Free Buchwald–Hartwig (Hetero)arylation of Anilines, Diarylamines, and Dialkylamines Mediated by Expanded‐Ring N‐Heterocyclic Carbene Palladium Complexes

AbstractA highly efficient solvent‐free protocol for the Buchwald–Hartwig (hetero)arylation of anilines, diarylamines, and dialkylamines mediated by the expanded‐ring N‐heterocyclic carbene palladium complex (THP‐Dipp)Pd(cinn)Cl [THP‐Dipp = 1,3‐bis(2,6‐diisopropylphenyl)‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidene; cinn = cinnamyl, 3‐phenylallyl] was developed. The catalytic protocol was efficient for the coupling of amines and (hetero)aryl chlorides and bromides bearing donor, acceptor, and bulky substituents.

A new N–heterocyclic carbene palladium complex immobilized on nano silica: An efficient and recyclable catalyst for Suzuki–Miyaura C[sbnd]C coupling reaction

A new catalytic system based on Pd–NHC complex utilizing (4–pyridyl)bis(imidazolyl)methane as a bidentate NHC ligand supported on nano‒silica is introduced. The catalyst was characterized by FT–IR spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy dispersive X–ray analysis, transmission electron microscopy and elemental analysis. This heterogeneous catalytic system exhibited excellent activity in the Suzuki–Miyaura coupling reaction of various aryl halides with phenylboronic acid, and was reusable several times without significant loss of its catalytic activity.