Carbene Palladium Complexes Research Articles

Chiral Biaryl N-Heterocyclic Carbene-Palladium Catalysts with Anagostic C-H···Pd Interaction for Enantioselective Desymmetric C-N Cross-Coupling.

Novel chiral biaryl imidazo[1,5-a]pyridine carbene-palladium complexes (ImPy-Pd) featuring an anagostic C-H···Pd interaction and a C5-aryl substituent have been developed and successfully applied to the Pd-catalyzed enantioselective desymmetric C-N cross-coupling of malonamide derivatives, providing chiral 3,4-dihydroquinoline-2-ones with quaternary stereocenters in high yields (≤99%) and enantioselectivities (≤97:3 er). The chiral catalyst exerts stereocontrol by restricting the rotation of substituents around the metal center through anagostic interactions with sterically bulky substituents.

Synthesis, Characterizations and Multivariate Data Analysis of Non- and Nitrile-Functionalized N-Heterocyclic Carbene Complexes of Silver(I) and Palladium(II)

Synthesis, Characterizations and Multivariate Data Analysis of Non- and Nitrile-Functionalized N-Heterocyclic Carbene Complexes of Silver(I) and Palladium(II)

Catalytic Properties of Sterically Shielded Carbene Complexes of Palladium in C–C and C–N Coupling Reactions of Haloarenes

Catalytic Properties of Sterically Shielded Carbene Complexes of Palladium in C–C and C–N Coupling Reactions of Haloarenes

Triazine-wingtips accelerated NHC-Pd catalysed carbonylative Suzuki cross-coupling reaction

Triazine conjugated N-heterocyclic carbene palladium complexes were synthesized for reducing the Pd amount in the catalysts to the ppm levels. This work reports the carbonylative Suzuki-Miyaura coupling of aryl iodides catalyzed by N-heterocyclic carbenes palladium with triazine wingtips (T-NHC-Pd). More importantly, the palladacycles have been used to generate high turnover numbers (TON's) and turnover frequencies (TOF's).

Metal-(Acyclic Diaminocarbene) Complexes Demonstrate Nanomolar Antiproliferative Activity against Triple-Negative Breast Cancer.

Invited for the cover of this issue are Tatiyana Serebryanskaya, Mikhail Kinzhalov and co-workers at St. Petersburg State University, the Research Institute for Physical Chemical Problems, Belarusian State University, Togliatti State University and Blokhin National Medical Research Center of Oncology. The image depicts the shield of Pallas Athena with the structure of a palladium carbene complex that protects against triple-negative breast cancer. Read the full text of the article at 10.1002/chem.202400101.

Mixed N‐heterocyclic carbene and benzyl‐, phenethyl‐, and biphenylamine coordinated Pd complexes: Anticancer activities and stereo‐electronic effects

A series of mixed N‐heterocylic carbene (NHC) palladium complexes bearing C^N bidentate ligands derived from benzylamine, phenethylamine, and biphenylamine were prepared and fully characterized by NMR spectroscopy, ESI‐MS spectrometry, and X‐ray diffraction analyses. The complexes were potent in inhibiting proliferation of HepG2 and Caco2 cancer cells, and a SAR (structure–activity relationship) study revealed C^N ligands with stronger electron donation and moderate steric hindrance are more cytotoxic. DNA binding study through UV–vis absorption titration indicated that such complexes bound stronger to CT‐DNA molecules with higher binding constants. Additional molecular docking of the best performer suggested a groove binding mode through hydrogen bonding and π‐π stacking interactions. The apoptosis induced by the two best performers of α,α‐dimethylbenzylamine and S‐α‐methylbenzylamine ligated complexes was further analyzed by morphology change, cell cycle distribution, ROS production, and mitochondrial membrane potential studies.

(SC,RS)-Bromido-(N-{4-methyl-1-[(4-methyl-phenyl)sul-fan-yl]-pentan-2-yl}-N'-(pyridin-2-yl)imidazol-2-yl-idene)palladium(II) bromide.

The mol-ecule of the title NCNHCS pincer N-heterocyclic carbene palladium(II) complex, [PdBr(C21H25N3S)]Br, exhibits a slightly distorted square-planar coordination at the palladium(II) atom, with the five-membered chelate ring nearly planar. The six-membered chelate ring adopts an envelope conformation. Upon chelation, the sulfur atom becomes a stereogenic centre with an RS configuration induced by the chiral carbon of the precursor imidazolium salt. There are intra-molecular C-H⋯Br-Pd hydrogen bonds in the structure. The two inter-stitial Br atoms, as the counter-anion of the structure, are both located on crystallographic twofold axes and are connected to the complex cations via C-H⋯·Br hydrogen bonds.

Structural and catalytic studies of Six-Membered amino N-Heterocyclic carbene palladium (II) complexes with a triazine backbone for Suzuki coupling reaction

This work enhances to our understanding of the triazine ligand’s impact on the catalytic activity of N-heterocyclic carbene palladium complexes in Suzuki coupling reactions. All synthesized Pd complexes were characterized using single-crystal X-ray diffraction and elemental analysis. A series of mononuclear, structurally defined six-membered ring NHC palladium complexes supported by various donor ligands were synthesized, and the Suzuki coupling reactions were performed under mild conditions. The results showed that the nitrogen-based ligand outperformed other ligands in terms of yield, highlighting its potential for further development and optimization. The Suzuki coupling reactions were carried out in air and at ambient temperature or 70 °C, depending on whether aryl bromides or aryl chlorides were used as substrates, yielding moderate to high yields in a short time.

Rational design of galactopyranoside-substituted N-heterocyclic carbene palladium(ii) complexes. Stable and efficient catalyst for C-C coupling in aqueous media.

Following a rational design, three novel palladium(ii) complexes bearing galactopyranoside-based N-heterocyclic carbene ligands have been synthesized via transmetalation of the corresponding Ag(i) complexes. Palladium(ii) complexes have been characterized by NMR, FT-IR and elemental analysis. Catalytic studies, using the Stille and Suzuki-Miyaura cross-coupling reactions as model C-C coupling, reveal that the complexes are active and reusable. The best results in terms of TON values were achieved in aqueous medium using either the in situ deacetylation of the catalyst or the previously deacetylated catalyst. The catalytic condition using in situ deacetylation was more efficient because it avoids an additional deprotection step.

A redox switchable ferrocene decorated n-heterocyclic carbene (NHC) palladium catalyst for cross coupling of arylboronic acid and acetic anhydride in phosphine, base and additive free conditions

A phosphine, base and additive free cross-coupling of arylboronic acid is reported via C–O bond cleavage of acetic anhydride using a switchable ferrocene functionalized n-heterocyclic carbene (NHC) palladium complex.

Solvent-Free Buchwald-Hartwig Amination of Heteroaryl Chlorides by N-Heterocyclic Carbene-Palladium Complex (SIPr)Ph2Pd(cin)Cl at Room Temperature.

Using the robust N-heterocyclic carbene-palladium complex (SIPr)Ph2Pd(cin)Cl, a highly efficient and easy-to-operate method has been developed at room temperature for the solvent-free Buchwald-Hartwig amination of heteroaryl chlorides with various amines. The amount of catalyst can be as low as 0.05 wt %. The system was demonstrated on 47 substrates and successfully applied to the synthesis of commercial pharmaceuticals and candidate drugs with high yields. Furthermore, the protocol can be used to prepare aniline derivatives on a multigram scale without yield loss.

Accessing Heteroannular Benzoxazole and Benzimidazole Scaffolds via Carbodiimides Using Azide-Isocyanide Cross-Coupling as Catalyzed by Mesoionic Singlet Palladium Carbene Complexes Derived from a Phenothiazine Moiety.

The coupling of aryl and aliphatic azides with isocyanides yielding carbodiimides (8-17) were efficiently catalyzed by well-defined structurally characterized trans-(MIC)PdI2(L) [MIC = 1-CH2Ph-3-Me-4-(CH2N(C6H4)2S)-1,2,3-triazol-5-ylidene, L = NC5H5 (4), MesNC (5)], trans-(MIC)2PdI2 (6), and cis-(MIC)Pd(PPh3)I2 (7) type palladium complexes, which incidentally mark the first instances of the use of mesoionic singlet palladium carbene complexes for the said application. As observed from the product yields, the catalytic activity varied in the order 4 > 5 ∼ 6 > 7 for these complexes. A detailed mechanistic studies indicated that the catalysis proceeded via a palladium(0) (4a-7 a) species. Using a representative palladium precatalyst (4), the azide-isocyanide coupling was successfully extended to synthesizing two different bioactive heteroannular benzoxazole (18-22) and benzimidazole (23-27) derivatives, thereby broadening the scope of the catalytic application.

Synthesis and Antimicrobial Activity of Carbene Complexesof the Imidazole, Benzimidazole and 1,2,4‐Triazole Series

AbstractNew carbene complexes of copper (I), silver and palladium, including ionic carbene‐phenanthroline complexes, were synthesized on the basis of imidazole, benzimidazole, 1,2,4‐triazole systems with cetyl and aryl including fluorophenyl substituents. The study of the antimicrobial action of the synthesized compounds revealed high antibacterial and antifungal activities of fluoro‐ and phenanthroline‐containing carbene complexes.

Synthesis and Studies Pd(II)-NHC complexes with thiosaccharinate, saccharinate or benzothiazolinate ligands

Three cis-chelating di-N-heterocyclic carbene palladium(II) complexes [Pd(X)2(di- NHC)] (X= tsac, sac and bit) tsac= thiosaccharinate, sac= saccharinate, bit= benzisothiazolinate, bearing different anionic co-ligand was synthesized and characterized. A series of palladium(II) complexes (2-5) bearing cis-chelating homo-dicarbene ligand with varying propylene-bridged (C3) and N-heterocyclic backbones (imidazole) have been synthesized by reaction of [Pd(OAc)2] with the respective diazolium bromides in DMSO, have been prepared and characterized by elemental analysis, infrared spectra and 1H NMR. These compounds are all stabilized in the sold state. The bidentate (diNHC) ligand together with two N-coordenated sac , bit and two S-coordenated tsac ligand, from the square planar coordination geometry around the palladium(II) ion.

Nitron-derivative-based palladium carbene complexes: structural characterization, theoretical calculations, and catalytic applications in the Mizoroki-Heck coupling reaction.

New palladium(0) and palladium(ii) complexes with N-heterocyclic carbene (NHC) ligands derived from nitron and its derivatives were synthesized. The structures of most of these complexes were established by single-crystal X-ray diffraction studies. Among the new complexes, the palladium complex with a monodentate NHC ligand derived from nitron demonstrated the highest efficacy as a catalyst precursor in the Mizoroki-Heck coupling reaction of aryl chlorides with alkenes. Theoretical calculations provide valuable insights into the electronic parameters of both the ligands and the palladium complexes, highlighting the significance of a robust Pd-C bond and the π-accepting property of the NHC ligand in achieving enhanced catalytic activity. Notably, catalyst activation occurred much more rapidly with the preformed palladium(0) complex compared to its palladium(ii) counterpart.

Mechanism of Carbon-Carbon Coupling Reactions Catalyzed by Imine-Ligand-Assisted N-Heterocyclic Carbene Palladium Complexes

Mechanism of Carbon-Carbon Coupling Reactions Catalyzed by Imine-Ligand-Assisted N-Heterocyclic Carbene Palladium Complexes

Novel PEPPSI-type N-heterocyclic carbene palladium(II) complexes: Synthesis, characterization, in silico studies and enzyme inhibitory properties against some metabolic enzymes

In this study, a series of PEPPSI-type N-heterocyclic carbene palladium(II) complexes 3a-e were synthesized using amine functionalized benzimidazolium salts 2a-e as N-heterocyclic carbene precursors. These complexes were characterized by FT-IR, 1H NMR and 13C NMR spectroscopy, elemental analysis and mass spectrometry. Also, the molecular and crystal structure of 3b has been determined by the single-crystal X-ray diffraction method. According to the structural analysis, the geometry of the palladium center of the complex adopts a slightly distorted square planar environment. The benzimidazolium salts 2a-e and their palladium(II) complexes 3a-e were screened for human carbonic anhydrase I, II (hCAs I and II), and α-glycosidase inhibitory activities. Results indicated that all the synthetic compounds exhibited potent inhibitory activities against all targets as compared to the standard inhibitors, revealed by IC50 values. Ki values of 2a-e and 3a-e for hCA I, hCA II, and α-glycosidase enzymes were obtained in the ranges 1.17 ± 0.11–65.50 ± 8.20 µM, 1.02 ± 0.08–57.60 ± 6.41 µM, and 118.86 ± 11.92–509.21 ± 26.61 nM, respectively. Besides these, molecular docking calculations of potent compounds 2b, 2d, 2e, 3a, 3b, 3c and 3e towards human carbonic anhydrase I (hCA I), human carbonic anhydrase II (hCA II), and α-glycosidase (α-Gly) were presented using AutoDock 4. Among the compounds discussed, compounds 3c, 3a, 2e and 2b have the best binding affinity for α-Gly (-9.87, −9.77, −9.04 and −8.63 kcal/mol); compounds 3e, 3b, 2d and 2e turn out to have the second-best binding affinity (-8.80, −8.74, −8.39 and −7.57 kcal/mol) against hCA II. Lastly, compounds showing the lowest binding affinity for hCA I enzyme are 3e, 3b, 2d and 2e, respectively. These findings show that especially NHC-palladium(II) complexes 3a-e are more active for all three enzyme structures than their N-heterocyclic carbene precursors 2a-e and may be potential candidates for the discovery and development of effective inhibitors for the related enzymes in the future.

Corrigendum: Synthesis and Structures of Benzyl‐ and Amido‐Substituted N‐Heterocyclic Palladium Carbene Complexes

Corrigendum: Synthesis and Structures of Benzyl‐ and Amido‐Substituted N‐Heterocyclic Palladium Carbene Complexes

Bis(imino)acenaphthene N‐Heterocyclic Carbene Palladium Complexes Bearing Tertiary Amines: Structural and Catalytic Studies on the Interaction between Soft Acid and Hard Base

AbstractThe HSAB principle in designing Bis(imino)acenaphthene N‐heterocyclic carbene (NHC) palladium complexes is presented. N‐donor ligands serve as hard bases to enhance the catalytic activities of NHC Pd complexes in Suzuki and Buchwald–Hartwig amination reactions. The Pd complex bearing tertiary amine ligands exhibited higher performance in coupling reactions than those exhibited by other soft base ligands reported in literature. 48 coupling products were generated in moderate‐to‐complete yields in the presence of aryl chlorides as substrates for Suzuki and amination reactions in air under mild conditions.

Synthesis and Structures of Benzyl‐ and Amido‐Substituted N‐Heterocyclic Palladium Carbene Complexes

AbstractThe benzyl‐ and amido‐substituted benzimidazolium ligand precursor [Bz‐BimH‐CH2CONH2]Br (1) was synthesized. Under different conditions, the reactions of this ligand precursor with PdBr2 produced palladium carbene complexes: Pd[(Bz‐Bim‐CH2CONH2)2Br2] (2), Pd(Bz‐Bim‐CH2CONH)2 (3), [Pd(Bz‐Bim‐CH2CONH2)(Py)Br2] (4), or [Pd(Bz‐Bim‐CH2CONH2)(CH3CN)Br2] (5). These complexes were characterized by NMR, IR, and single‐crystal X‐ray diffraction analyses. Complex 2 contains two trans rotamers in both the solution and solid state, and a crystal that possesses a trans‐anti conformation is confirmed through single‐crystal X‐ray diffraction analysis. Complex 3 contains two cis‐orientated bidentate carbene ligands, and complexes 4 and 5 are mono‐carbene complexes. The chelate rings in complex 3 rendered the methylene protons of the amido‐substituted diastereotopic, and a long range (six bond) through bond interaction between the carbonyl carbon and the methylene protons of the benzyl‐substituent was observed through the HMBC experiment. The catalytic activity studies indicated 4 and 5 are better catalysts in Suzuki‐Miyaura coupling reaction.