Tunable bis(pyridinium amidate) ligands efficiently promote palladium-catalyzed ethylene polymerization

Electronic effects of amine-imine nickel and palladium catalysts on ethylene (co)polymerization

Complete synthetic, structural, and biomedical studies of two Pd complexes as well as Au and Ag complexes of 1-benzyl-3-tert-butylimidazol-2-ylidene are reported. Specifically, trans-[1-benzyl-3-tert-butylimidazol-2-ylidene]Pd(pyridine)Cl2 (1a) was synthesized from the reaction of 1-benzyl-3-tert-butylimidazolium chloride (1) with PdCl2 in the presence of K2CO3 as a base. The other palladium complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]2PdCl2 (1b), and a gold complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]AuCl (1c), were synthesized by following a transmetallation route from the silver complex, [1-benzyl-3-tert-butylimidazol-2-ylidene]AgCl (1d), by treatment with (COD)PdCl2 and (SMe2)AuCl, respectively. The silver complex 1d in turn was synthesized by the reaction of 1 with Ag2O. The molecular structures of 1a-d have been determined by X-ray diffraction studies. Biomedical studies revealed that, while the palladium complexes 1a and 1b displayed potent anticancer activity, the gold (1c) and silver (1d) complexes exhibited significant antimicrobial properties. Specifically, 1b showed strong antiproliferative activity against three types of human tumor cells, namely, cervical cancer (HeLa), breast cancer (MCF-7), and colon adenocarcinoma (HCT 116), in culture. The antiproliferative activity of 1b was found to be considerably stronger than that of cisplatin. The 1b complex inhibited tumor cell proliferation by arresting the cell cycle progression at the G2 phase, preventing the mitotic entry of the cell. We present evidence suggesting that the treated cells underwent programmed cell death through a p53-dependent pathway. Though both the gold (1c) and silver (1d) complexes showed antimicrobial activity toward Bacillus subtilis, 1c was found to be ca. 2 times more potent than 1d.

A Distinctive Pattern for Substituent Effects on Transition Metal Centers: Enhanced Electron-Donating Capacity of Cationic Palladium Species

Reversion of the chain walking ability of α-diimine nickel and palladium catalysts with bulky diarylmethyl substituents

The newly designed tridentate ligand, 2-((2-aminophenyl)diazenyl)-N-benzylaniline, 1 has been synthesized by the reaction between 2,2′-diaminoazobenzene and benzyl chloride in presence of K2CO3. This ligand was reacted with Na2[PdCl4] in methanol to give the new Pd(II) complex 2. Both the ligand and complex were characterized by usual spectroscopic techniques. Furthermore, the solid-state structure of complex 2 was determined using single crystal X-ray diffraction analysis. It revealed that the ligand binds with Pd(II) in dianionic tridentate (N,N,N) fashion offering distorted square planar geometry where fourth position is occupied by one phosphine ligand. The performance of the Pd(II) phosphine complex as catalyst was evaluated in the homogenous Suzuki and Heck reactions under mild conditions in presence of air and moisture. The Pd(II) complex showed good catalytic activities for the coupling of several aryl halides (iodides and bromides) with phenyl boronic acid and styrene providing excellent yields. After catalytic reactions, the catalyst has been recovered by simple chromatographic separation and reused for next reaction and its activity checked up to three cycles without sufficient loss. The newly designed tridentate ligand, 2-((2-aminophenyl)diazenyl)-N-benzylaniline and its corresponding palladium(II) complex were synthesized and structurally characterized. The neutral palladium(II) amido complex with phosphine as ancillary ligand was formed through two amino proton elimination from ligand precursor. The newly synthesized Palladium(II) complex acts as potential catalyst toward C–C bond formation for a variety of substrate under mild conditions in presence of air and moisture.

Facile Access to Polar-Functionalized Ultrahigh Molecular Weight Polyethylene at Ambient Conditions

Abstract:: This comprehensive review explores the advancements in catalytic transformation, focusing on the use of heterogeneous catalytic systems with a particular emphasis on polymeric-supported palladium (Pd) complexes. This study explores the limitations associated with conventional homogeneous reagents, emphasizes the transition to eco-friendly catalytic systems, and emphasizes the importance of Pd nanoparticles. These nanoparticles are particularly noteworthy for their distinctive properties, including elevated catalytic activity, making them promising for various applications in organic synthesis. The review thoroughly examines the design and synthesis of heterogeneous catalysts, emphasizing the crucial selection of safe and recyclable supports to augment the longevity and reusability of metallic catalysts. Diverse polymer varieties, including polystyrene (PS), polyethylene (PE), polyacrylate derivatives, polyethylene glycol (PEG), and grafted polymers, are investigated as viable supports for Pd complexes. The authors intricately describe the synthesis techniques for these polymer-supported Pd catalysts and furnish illustrative examples showcasing their effectiveness in organic transformation. This comprehensive review additionally highlights the synthesis of polymer-supported palladium (Pd) materials and discusses their applications in electrochemistry. The focus extends to the electrocatalytic properties of Pdbased polymeric nanomaterials, showcasing their effectiveness in glucose sensing, hydrogen peroxide detection, and the sensing of other biological analytes. Furthermore, the catalytic capabilities of Pd nanoparticles in various electrochemical applications, including wastewater treatment and electrochemical capacitors, are explored. Integrating polymer-supported Pd materials into these electrochemical processes underscores their versatility and potential contributions to advancements in catalysis and electrochemical sensing. Catalytic applications featuring polymer-supported palladium complexes with polymeric ligands in organic synthesis processes use the Sonogashira reaction, Suzuki-Miyaura coupling, Heck reaction, Catalytic asymmetric transformations, etc. The subsequent section of the paper focuses on the creation of polymeric palladium complexes, achieved by the complexation of polymeric ligands with palladium precursors. It delves into noteworthy examples of catalytic processes employing polymer-supported palladium complexes featuring polymeric ligands, emphasizing distinct polymers, such as PS, PE, polyacrylate derivatives, PEG, and grafting polymers. The review concludes by exploring catalytic asymmetric transformations using chiral palladium complexes immobilized on polymer supports and discusses various chiral ligands and their immobilization on polymer supports, emphasizing their application in asymmetric allylic alkylation. The review furnishes a comprehensive summary of recent advancements, challenges, and prospective avenues in catalytic oxidation facilitated by polymer- supported palladium catalysts with electrochemical applications.

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We herein report the two novel well-defined palladium(II) complexes 1(b−c), of the chiral N-fused tricyclic 1,2,3-triazolium-derived mesoionic carbenes (MIC) ligand 1a. The chiral tricyclic PEPPSI type complex namely, trans-{2-methyl-(5aS,9aS)-5a,6,7,8,9,9a-hexahydro-4H-benzo[b][1,2,3]triazolo[1,5-d][1,4]oxazin-3-ylidene}PdI2(pyridine)} (1b), and the chiral tricyclic bis(tz-MIC)-palladium complex namely, {2-methyl-(5aS,9aS)-5a,6,7,8,9,9a-hexahydro-4H-benzo[b][1,2,3]triazolo[1,5-d][1,4]oxazinium-3-ylidene}2PdCl2} (1c). The chiral tricyclic (tz-MIC)PdI2(pyridine) type PEPPSI complex (1b) was obtained by direct reaction of the corresponding chiral tricyclic 1,2,3-triazolium-derived mesoionic carbenes (MIC) ligand 1a, by treatment with PdCl2 in the presence of K2CO3 as a base in pyridine in 87% yield. (Scheme 1). The chiral tricyclic 1,2,3-triazolium iodide salt (1a) was converted to its in-situ silver analogue by reaction with Ag2O and then subsequently upon treatment with (COD)PdCl2 to produce the chiral tricyclic (tz-MIC)2PdCl2 type palladium complex (1c). All these palladium complexes were isolated for the first time and structurally characterized by 1H NMR and 13C{1H}-NMR spectroscopy, FT-IR spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray crystallography.

Pd complexes have been used in catalytic conversion of primary and secondary amines into isocyanates or carbamoyl chlorides, respectively. The latter have been used as intermediates for the synthesis of carbamates and ureas. The palladium-based catalytic system is very active and operates in two steps, avoiding the synthesis of phosgene (COCl2), but making use of CO and Cl2 as in phosgene chemistry. In the first step the palladium(II) complex PdCl2L2 [L2 = 2,2‘ dipyridine (dipy) or 1,10-phenantroline (phen); L = triphenylphosphine (PPh3)] reacts with the amine [NH2R, R = n-C3H7 (a), n-C4H9 (b), n-C5H11 (c); NHRR‘, NRR' = CH2(CH2)4N (d), CH2(CH2OCH2)CH2N (e)] and CO to produce the carbamoyl complexes PdCl(CONHR)L2 and PdCl(2-x)(CONRR‘)xL2 (x = 1, 2). When primary amines NH2R, (a, b, and c) are used, only monocarbamoyl complexes [PdCl(CONHR)(dipy) (1a−c), PdCl(CONHR)(phen) (2a−c), and PdCl(CONHR)(PPh3)2 (3a,b)] are isolated. Secondary amines NHRR‘ (d and e) afford both monocarbamoyl PdCl(CONRR‘)(dipy) (4d,e) and PdCl(CONRR‘)(phen) (5d,e) and dicarbamoyl complexes, Pd(CONRR‘)2(dipy) (6d,e) and Pd(CONRR‘)2(phen) (7d). 4d and 6d have been structurally characterized: they are the first example of mono- and dicarbamoyl complexes, respectively, of the same metal system for which the solid state structure is reported.The carbamoyl complexes are subsequently reacted with halogen donors (CuCl2, N-chlorosuccinimide, Cl2, I2) with elimination of the carbamoyl ligand as isocyanate (primary amines complexes 1−3) or carbamoyl chloride (secondary amines complexes 4−7) and quantitative formation of the starting Pd(II) complex. Cl2 and I2 are most effective and selective. They do not generate byproducts and allow an easy and quantitative recovery of the catalyst, making the reaction of potential utility.

Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization. This type of catalyst features six-membered chelate ring size, and can enable the copolymerizations of ethylene with a wide variety of polar monomers. In this contribution, we decide to investigate the influence of chelate ring size on the properties of phosphine-sulfonate palladium catalysts. As such, a series of phosphine-sulfonate ligands and the corresponding seven-membered ring Pd(II) complexes [ κ 2-( P , O )-2-(CH2- P R1R2)-4-methylphenyl-sulfonato]Pd(Me) (DMSO) ( Pd1 , R1=R2=Cy, Pd2 , R1=R2= o -MeO-C6H4; Pd3 , R1=Ph, R2=2-[2,6-(MeO)2C6H3]C6H4; DMSO=dimethyl sulfoxide) were designed, prepared and characterized. These palladium complexes are moderately active when they were applied in ethylene polymerization and copolymerizations with methyl acrylate and butyl vinyl ether. However, their properties are greatly reduced from those of the classic six-membered ring phosphine-sulfonate palladium complex Pd2 ′. The experimental results indicate that the bigger chelate ring size can increase the ligand flexibility and damage the catalytic properties for the phosphine-sulfonate type palladium catalysts.

Thermally robust α-diimine nickel and palladium catalysts with constrained space for ethylene (co)polymerizations

Direct synthesis of polar functionalized linear low density polyethylene (LLDPE) using slow-chain-walking palladium catalysts

Dna-binding and antiproliferative properties of Palladium(II) complexes with tridentate ligands

The objective of this study was to determine the effect of 1-methylcyclopropene (1-MCP) on vase life of rose cv. Osiana in different storage conditions and in the presence of exogenous ethylene. The roses were treated with 0.5; 1.0; 1.5 and 2.0 g m-3 of Ethylbloc?, and submitted to the following conditions: Storage at 5 °C with stems in water; Storage at 22 °C with stems in water; Storage at 5 °C in ‘Strong’ type paper for 3 days and subsequent storage at 22 °C. The best storage condition was at 22 °C with the stems in the water. Doses greater than 1.0 g m-3 of Ethylbloc? prolonged vase life. In this condition, the stems were treated with 1.0 g m-³ Ethylbloc?; 1.0 g m-3 Ethylbloc? + 10 ?L L-1 ethylene and 10 ?L L-1 ethylene for 24 h. The Ethylbloc? increased vase life even in the presence of ethylene and fresh mass on the first two days. It reduced ethylene production by flowers in the first 24 h, and respiratory activity after 36 h. It can be concluded that the concentration of 1.0 g m-3 of Ethylbloc? prolongs the vase life of cv. Osiana stored at room temperature with the stems in water even in the presence of exogenous ethylene.