Showing papers on "Pyridine published in 2021"

Pyridine Detection Using Supramolecular Organic Frameworks Incorporating Cucurbit[10]uril.

Abstract: A physical impregnation method is presented in this study, providing a facile approach to encapsulating functional guest molecules (GMs) into robust crystalline supramolecular organic frameworks incorporating cucurbit[10]uril (Q[10]-SOF) As Q[10]-SOF has high evaporated pyridine affinity under normal atmospheric pressure, pyridine molecules in this method were successfully encapsulated into the nanospace formed by GMs and Q[10]-SOF while retaining their crystal framework, morphology, and high stability GMs@Q[10]-SOF solid materials were found to respond to pyridine, being suitable to be used as solid sensors Notably, Q[10]-SOF loading with pyrene exhibited a unique response to pyridine along with dramatic fluorescence quenching; loading with dansyl chloride exhibited a unique response to pyridine along with significant fluorescence enhancement, having a quick response within 60 s Our findings represent a critical advancement in the design of pyridine detection and adsorption for commercial gas identification and sensing

A tautomeric ligand enables directed C‒H hydroxylation with molecular oxygen

Abstract: Hydroxylation of aryl carbon-hydrogen bonds with transition metal catalysts has proven challenging when oxygen is used as the oxidant. Here, we report a palladium complex bearing a bidentate pyridine/pyridone ligand that efficiently catalyzes this reaction at ring positions adjacent to carboxylic acids. Infrared, x-ray, and computational analysis support a possible role of ligand tautomerization from mono-anionic (L,X) to neutral (L,L) coordination in the catalytic cycle of aerobic carbon-hydrogen hydroxylation reaction. The conventional site selectivity dictated by heterocycles is overturned by this catalyst, thus allowing late-stage modification of compounds of pharmaceutical interest at previously inaccessible sites.

Pyridine-Conjugated Pillar[5]arene: From Molecular Crystals of Blue Luminescence to Red-Emissive Coordination Nanocrystals.

Abstract: A luminescent molecular crystal (P5bipy) and a Cu(I)-coordinated luminescent nanocrystal (Cu(I)-P5bipy) have been prepared concurrently using one conjugated pillar[5]arene macrocycle via a facile supramolecular self-assembling strategy. The molecular crystal shows enhanced luminescence compared with unmodified pillar[5]arene, attributed to its conjugated structure and staggered packing mode, while the coordination nanocrystal exhibits well-defined crystalline structures and long-lifetime triplet state emission along with pronounced solvochromic features.

A directive Ni catalyst overrides conventional site selectivity in pyridine C-H alkenylation.

Abstract: Achieving the transition metal-catalysed pyridine C3-H alkenylation, with pyridine as the limiting reagent, has remained a long-standing challenge. Previously, we disclosed that the use of strong coordinating bidentate ligands can overcome catalyst deactivation and provide Pd-catalysed C3 alkenylation of pyridines. However, this strategy proved ineffective when using pyridine as the limiting reagent, as it required large excesses and high concentrations to achieve reasonable yields, which rendered it inapplicable to complex pyridines prevalent in bioactive molecules. Here we report that a bifunctional N-heterocyclic carbene-ligated Ni-Al catalyst can smoothly furnish C3-H alkenylation of pyridines. This method overrides the intrinsic C2 and/or C4 selectivity, and provides a series of C3-alkenylated pyridines in 43-99% yields and up to 98:2 C3 selectivity. This method not only allows a variety of pyridine and heteroarene substrates to be used as the limiting reagent, but is also effective for the late-stage C3 alkenylation of diverse complex pyridine motifs in bioactive molecules.

Multistage Self-Assembly Strategy: Designed Synthesis of N-doped Mesoporous Carbon with High and Controllable Pyridine N Content for Ultrahigh Surface-Area-Normalized Capacitance

Abstract: Nitrogen doping could improve the performance of carbon materials in electrocatalysis, CO2 adsorption, and energy storage. [1]However, the control of the doping type and the amount of nitrogen (N)-...

Single-Cell Chemistry of Photoactivatable Platinum Anticancer Complexes.

Abstract: The Pt(IV) prodrug trans, trans, trans-[Pt(pyridine)2(N3)2(OH)2] (Pt1) and its coumarin derivative trans, trans, trans-[Pt(pyridine)2(N3)2(OH)(coumarin-3-carboxylate)] (Pt2) are promising agents fo...

Magnetically recoverable catalysts for the preparation of pyridine derivatives: an overview

Abstract: Magnetically recoverable nano-catalysts can be readily separated from the reaction medium using an external magnet. In recent years, chemistry researchers have employed them as catalysts in chemical reactions. The high surface area, simple preparation, and modification are among their major advantages. Pyridine derivatives are an important category of heterocyclic compounds, which show a wide range of excellent biological activities, including IKK-β inhibitors, anti-microbial agents, A2A adenosine receptor antagonists, inhibitors of HIV-1 integrase, anti-tumor, anti-inflammatory, and anti-Parkinsonism. Recently, the catalytic activity of magnetic nanoparticles was investigated in multicomponent reactions in the synthesis of pyridine derivatives, which is discussed in this review.

Molecular dynamics, DFT and electrochemical to study the interfacial adsorption behavior of new imidazo[4,5-b] pyridine derivative as corrosion inhibitor in acid medium

Abstract: The present paper discusses the adsorption and inhibitory effect of a new pyridine derivative, namely, 6-bromo-2-(4-methoxyphenyl)-3-nonyl-3H-imidazo[4,5-b] pyridine (PIP) on mild steel corrosion in molar hydrochloric acid medium. The experimental study was carried out using a series of techniques such as weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The effectiveness of this compound reaches a maximum value of 92% at 10–4 M. The obtained results showed that the adsorption process on the metal surface follows the Flory–Huggins adsorption model. Scanning electron microscopy (SEM) confirmed the existence of an adsorption film on the MS. The relationship between the corrosion inhibition efficiency and the molecular electronic properties of the studied compound were performed using Quantum chemistry method at the level of DFT/B3LYP at 6-31G (d,p) basis set. Quantum chemical calculations indicated that the investigated molecule has a tendency to be protonated in the acid medium. Molecular dynamics (MD) simulations were performed to evaluate the reactivity (interactions) of the system Fe (110) surface/PIP in HCl. A very good agreement was recorded with the experimental data.

Efficient Copolymerization of Acrylate and Ethylene with Neutral P, O-Chelated Nickel Catalysts: Mechanistic Investigations of Monomer Insertion and Chelate Formation.

Abstract: The efficient copolymerization of acrylates with ethylene using Ni catalysts remains a challenge. Herein, we report two neutral Ni(II) catalysts (POP-Ni-py (1) and PONap-Ni-py (2)) that exhibit high thermal stability and significantly higher incorporation of polar monomer (for 1) or improved resistance to tert-butylacrylate (tBA)-induced chain transfer (for 2), in comparison to previously reported catalysts. Nickel alkyl complexes generated after tBA insertion, POP-Ni-CCO(py) (3) and PONap-Ni-CCO(py) (4), were isolated and, for the first time, characterized by crystallography. Weakened lutidine vs pyridine coordination in 2-lut facilitated the isolation of a N-donor-free adduct after acrylate insertion PONap-Ni-CCO (5) which represents a novel example of a four-membered chelate relevant to acrylate polymerization catalysis. Experimental kinetic studies of six cases of monomer insertion with aforementioned nickel complexes indicate that pyridine dissociation and monomer coordination are fast relative to monomer migratory insertion and that monomer enchainment after tBA insertion is the rate limiting step of copolymerization. Further evaluation of monomer insertion using density functional theory studies identified a cis-trans isomerization via Berry-pseudorotation involving one of the pendant ether groups as the rate-limiting step for propagation, in the absence of a polar group at the chain end. The energy profiles for ethylene and tBA enchainments are in qualitative agreement with experimental measurements.

6s-3d {Ba3Zn4}-Organic Framework as an Effective Heterogeneous Catalyst for Chemical Fixation of CO2 and Knoevenagel Condensation Reaction.

Abstract: The exquisite combination of Ba2+ and Zn2+ with the aid of 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H6TDP) under the condition of solvothermal self-assembly generates one highly robust [Ba3Zn4(CO2)12(HCO2)2(OH2)2]-organic framework of {[Ba3Zn4(TDP)2(HCO2)2(OH2)2]·7DMF·4H2O}n (NUC-27), in which adjacent 2D layers are interlaced via hydrogen-bonding interactions to form a 3D skeleton with peapod-like channels and nano-caged voids. It is worth emphasizing that both Ba2+ and Zn2+ ions in NUC-27 display the extremely low coordination modes: hexa-coordinated [Ba(1)] and tetra-coordinated [Ba(2), Zn(1), and Zn(2)]. Furthermore, to the best our knowledge, NUC-27 is one scarcely reported 2D-based nanomaterial with an unprecedented Z-shaped hepta-nuclear heterometallic cluster of [Ba3Zn4(CO2)12(HCO2)2(OH2)2] as SBUs, which not only has plentiful low-coordinated open metal sites but also has the excellent physicochemical properties including omni-directional opening pores, ultrahigh porosity, larger specific surface area, and the coexistence of Lewis acid-base sites. Just as expected, thanks to its rich active metal sites and pyridine groups as strong Lewis acid-base roles, completely activated NUC-27 displays high catalytic efficiency on the chemical transformation of epoxides with CO2 into cyclic carbonates under mild conditions and effectively accelerates the reaction process of Knoevenagel condensation.

Lewis Acid Strength of Interfacial Metal Sites Drives CH 3 OH Selectivity and Formation Rates on Cu-Based CO 2 Hydrogenation Catalysts.

Abstract: CH3 OH formation rates in CO2 hydrogenation on Cu-based catalysts sensitively depend on the nature of the support and the presence of promoters. In this context, Cu nanoparticles supported on tailored supports (highly dispersed M on SiO2 ; M=Ti, Zr, Hf, Nb, Ta) were prepared via surface organometallic chemistry, and their catalytic performance was systematically investigated for CO2 hydrogenation to CH3 OH. The presence of Lewis acid sites enhances CH3 OH formation rate, likely originating from stabilization of formate and methoxy surface intermediates at the periphery of Cu nanoparticles, as evidenced by metrics of Lewis acid strength and detection of surface intermediates. The stabilization of surface intermediates depends on the strength of Lewis acid M sites, described by pyridine adsorption enthalpies and 13 C chemical shifts of -OCH3 coordinated to M; these chemical shifts are demonstrated here to be a molecular descriptor for Lewis acid strength and reactivity in CO2 hydrogenation.

A Fluorescence-Detected Coordination-Induced Spin State Switch.

Abstract: The response of the spin state to in situ variation of the coordination number (CISSS) is a promising and viable approach to smart sensor materials, yet it suffers to date from insensitive detection. Herein, we present the synthetic access to a family of planar nickel(II) complexes, whose CISSS is sensitively followed by means of fluorescence detection. For this purpose, nickel(II) complexes with four phenazine-based Schiff base-like ligands were synthesized and characterized through solution-phase spectroscopy (NMR and UV-vis), solid-state structure analysis (single-crystal XRD), and extended theoretical modeling. All of them reveal CISSS in solution through axial ligating a range of N- and O-donors. CISSS correlates nicely with the basicity of the axial ligand and the substitution-dependent acidity of the nickel(II) coordination site. Remarkably, three out of the four nickel(II) complexes are fluorescent in noncoordinating solvents but are fluorescence-silent in the presence of axial ligands such as pyridine. As these complexes are rare examples of fluorescent nickel(II) complexes, the photophysical properties with a coordination number of 4 were studied in detail, including temperature-dependent lifetime and quantum yield determinations. Most importantly, fluorescence quenching upon adding axial ligands allows a "black or white", i.e. digital, sensoring of spin state alternation. Our studies of fluorescence-detected CISSS (FD-CISSS) revealed that absorption-based CISSS and FD-CISSS are super proportional with respect to the pyridine concentration: FD-CISSS features a higher sensitivity. Overall, our findings indicate a favored ligation of these nickel(II) complexes in the excited state in comparison to the ground state.

Recent Developments in Transition-Metal-Free Functionalization and Derivatization Reactions of Pyridines

Abstract: Pyridine is an important structural motif that is prevalent in natural products, drugs, and materials. Methods that functionalize and derivatize pyridines have gained significant attention. Recently, a large number of transition-metal-free reactions have been developed. In this review, we provide a brief summary of recent advances in transition-metal-free functionalization and derivatization reactions of pyridines, categorized according to their reaction modes. 1 Introduction 2 Metalated Pyridines as Nucleophiles 2.1 Deprotonation 2.2 Halogen–Metal exchange 3 Activated Pyridines as Electrophiles 3.1 Asymmetric 2-Allylation by Chiral Phosphite Catalysis 3.2 Activation of Pyridines by a Bifunctional Activating Group 3.3 Alkylation of Pyridines by 1,2-Migration 3.4 Alkylation of Pyridines by [3+2] Addition 3.5 Pyridine Derivatization by Catalytic In Situ Activation Strategies 3.6 Reactions via Heterocyclic Phosphonium Salts 4 Radical Reactions for Pyridine Functionalization 4.1 Pyridine Functionalization through Radical Addition Reactions 4.2 Pyridine Functionalization through Radical–Radical Coupling Reactions 5 Derivatization of Pyridines through the Formation of Meisenheimer-Type Pyridyl Anions 6 Conclusion

Photocatalytic Oxidative Coupling of Arylamines for the Synthesis of Azoaromatics and the Role of O2 in the Mechanism.

Abstract: The photocatalytic oxidative coupling of aryl amines to selectively synthesize azoaromatic compounds has been realized. Multiple different photocatalysts can be used to perform the general reaction; however, Ir(dF-CF3-ppy)2(dtbpy)+, where dF-CF3-ppy is 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine and dtpby is 4,4'-tert-butyl-2,2'-bipyridine, showed the greatest range of reactivity with various amine substrates. Both electron-rich and -deficient amines can be coupled with yields up to 95% under an ambient air atmosphere. Oxygen was deemed to be essential for the reaction and is utilized in the regeneration of the photocatalyst. Fluorescence quenching and radical trap experiments indicate an amine radical coupling mechanism that proceeds through a hydrazoaromatic intermediate before further oxidation occurs to form the desired azoaromatic products.

Metal-free electrochemical C3-sulfonylation of imidazo[1,2-a]pyridines

Abstract: Electrochemical oxidative cross-coupling represents one of the most atom-economical and green approaches to synthesize various useful compounds. In this work, an electrochemical C3-sulfonylation of imidazo[1,2-a]pyridines with sodium benzenesulfinates as sulfonylation reagents has been developed. This transformation provides an effective and straightforward metal-free protocol towards the synthesis of biologically and synthetically useful 3-(arylsulfonyl)imidazo[1,2-a]pyridine. Up to 94% yields were obtained. The scale-up experiment gave 1.56 g of the desired product in 90% yield.

Transition metal complexes of a multidentate Schiff base ligand containing pyridine: synthesis, characterization, enzyme inhibitions, antioxidant properties, and molecular docking studies

Abstract: A series of Fe(II), Ni(II), and Pd(II) complexes were prepared with a novel Schiff base ligand containing pyridine moiety. The prepared compounds were characterized using FT-IR, 1H and 13 C NMR, UV–Vis, powder XRD, thermogravimetric analysis, mass spectra, magnetic susceptibility, and elemental analysis. The coordination geometry of Fe(II) and Ni(II) complexes were octahedral, where Fe(II) and Ni(II) metal ions were coordinated by an oxygen atom of the carbonyl group, a nitrogen atom of the azomethine moiety, and a phenolic oxygen atom. The Pd(II) complex had square planar geometry. All of the synthesized compounds were tested for their biochemical properties, including enzyme inhibition and antioxidant activities. According to the in vitro DPPH and FRAP antioxidant methods, the Schiff base ligand and its Fe(II)/Pd(II) complexes showed close antioxidant activities against the standards (BHA, BHT, ascorbic acid, and α-tocopherol). Enzyme inhibitions of the metal complexes were investigated against glutathione S-transferase (GST), acetylcholinesterase (AChE), and butyrylcholinesterase (BChE) enzymes. The best inhibition value (Ki) was observed for the Ni(II) complex against GST (2.63 ± 0.04 µM). Also, the Pd(II) complex showed the best inhibition value (10.17 ± 1.88 µM) against AChE. Molecular docking specified significant interactions at the active pockets of respective target enzymes. The Ni(II) complex exhibited good binding affinity against both BChE (− 9.0 kcal/mol and 9.36 ± 2.03 µM) and GST (− 7.0 kcal/mol and 2.63 ± 0.04 µM) enzymes.

Influence of Brønsted acid sites on chemoselective synthesis of pyrrolidones over H-ZSM-5 supported copper catalyst

Abstract: Cu(0)/H-ZSM-5 was identified as a chemoselective catalyst in the reductive amination of levulinic acid for the synthesis of pyrrolidones at ambient pressure and in aqueous media The chemoselective nature of Cu was explained by carbonyl interaction with surface Bronsted acid sites deduced by pyridine and acetone adsorbed in situ infrared (IR) spectroscopic studies in conjunction with N2O titration A strong polarization of band at 1685 cm−1 and an increase in its intensity with a decrease in Si/Al ratio of the H-ZSM-5 was found to be a key factor in the reductive amination activity Structure activity relationship was established using the physicochemical characteristics of the catalysts analyzed by XRD, BET-SA, H2-TPR, NH3-TPD and XPS analyses

Multicomponent design of chromeno[2,3-b]pyridine systems

Abstract: The review summarizes and systematizes data on the methods for the preparation of chromeno[2,3-b]pyridines. Both multicomponent and pseudo-multicomponent synthetic approaches and one-pot transformations based on the reactions of carbonyl compounds, malononitrile or its derivatives, and CH-acids are considered. Examples of the use of various catalysts, microwave and ultrasonic radiation, as well as electric current for the implementation of multicomponent transformations of this type are given. Characteristic features of the course and mechanisms of reactions are discussed. Data on the biological activity of the obtained compounds and on other fields of application of such heterocyclic systems are presented. The bibliography includes 109 references.

Design, synthesis and biological evaluation of heterocyclic methyl substituted pyridine Schiff base transition metal complexes

Abstract: In recent years heterocyclic Schiff base metal complexes attract more attention in biological application and also showing interesting co-ordination chemistry. In this research article a novel heterocyclic methyl-substituted pyridine Schiff base transition metal complexes of Fe(III), Co(III), Cu(II), and Ni(II) have been design and synthesized by reacting metal acetate or metal salts (FeCl3, CoOAc, CuOAc, NiOAc), with substituted heterocyclic ligand. All newly synthesized metalcomplexes were characterized by spectroscopic data and screened for elemental analysis, FT-IR, ESR, Magnetic susceptibility and TGA. The Electronic spectra and magnetic susceptibility measurements indicates that square planer and octahedral geometry of these complexes also suggest their structure in which (N, O) group acts as bidentate ligand. The thermal stability, decomposition rate and thermodynamic parameters of synthesized metal complexes were calculated by Freeman Carroll method. Also the biostatistical data of antimicrobial and anti-oxidant activities of synthesized metal complexes indicates moderate to good results.

Redox-Neutral Cobalt(III)-Catalyzed C-H Activation/Annulation of α,β-Unsaturated Oxime Ether with Alkyne: One-Step Access to Multisubstituted Pyridine.

Abstract: A redox neutral Co(III)-catalyzed annulation of α,β-unsaturated oxime ether with alkyne has been reported. Multisubstituted pyridines were synthesized in good yields without the use of any heavy me...

A new porous Co(II)-metal–organic framework for high sorption selectivity and affinity to CO2 and efficient catalytic oxidation of benzyl alcohols to benzaldehydes

Abstract: Herein, we report a new 3D porous Co(II)-based metal–organic framework catalyst (Me2NH2)2[Co3(L)2(H2O)2]·2DMF (MOF I), which has been successfully prepared by using Co(II) ions and rigid V-shaped 3,5-di(2,4-dicarboxylphenyl)pyridine (H4L) via the solvothermal reaction. Structural analysis reveals that I displays a porous structure with the pore size of 16.2 × 7.2 A2 based on the trinuclear [Co3(COO)4(H2O)2N2] secondary building units (SBUs). Gas sorption experiments on the guest free sample I′ reveals a high capacity and selectivity to CO2 over CH4. And further, the catalytic explorations of the I′-catalyzed system (I′: 3 mol%; proline: 40 mol%; CH3CN: 2 mL) reveal that benzyl alcohols with different structures can be efficiently transformed into benzyl alcohols without by-products under mild conditions.

Halogen Bonding Involving Palladium(II) as an XB Acceptor

Abstract: The half-lantern PdII2 complexes trans-(O,C)-[Pd(ppz)(μ-O∩N)]2 (1) and trans-(E,N)-[Pd(ppz)(μ-E∩N)]2 (E∩N is a deprotonated 2-substituted pyridine; E = S (2), Se (3); Hppz = 1-phenylpyrazole) were ...