Pyridine Substituents Research Articles

Bimetallic cyclometalated iridium complexes bridged by a BODIPY linker.

Presented here is a new class of supramolecular cyclometalated Ir(iii) complexes. The 2 : 1 assemblies include two phosphorescent cyclometalated Ir(iii) centers spanned by a BODIPY bridge with pyridine substituents at the β-pyrrole positions. The three complexes, which vary with respect to the cyclometalating ligand on iridium, are prepared via a simple one-pot procedure, with the target complexes isolated in 31-75% yield. The photophysics of these new compounds are described in detail. All complexes are strongly photoluminescent, with fluorescence from BODIPY being the dominant emission pathway. One member of the series has a near-unity photoluminescence quantum yield, significantly enhanced relative to the free BODIPY. The cyclometalating ligand on iridium controls the energy of the Ir-centered triplet excited state, but in all cases energy transfer from the Ir centers to the BODIPY quenches almost all phosphorescence. This work outlines a new, simple synthetic method for accessing supramolecular complexes.

A carbonylation path to a nylon precursor

Organic Chemistry Adipic acid and its esters are manufactured on a massive scale, primarily to produce nylon. However, the standard route requires large quantities of corrosive nitric acid. J. Yang et al. present an efficient alternative route whereby a palladium catalyst adds carbon monoxide to each end of butadiene (see the Perspective by Schaub). Both reactants are available at commodity scale, and the reaction produces no by-products. An optimized bidentate phosphine ligand bearing a pyridine substituent for proton shuttling proved key to attaining the necessary selectivity. Science , this issue p. [1514][1]; see also p. [1448][2] [1]: /lookup/doi/10.1126/science.aaz1293 [2]: /lookup/doi/10.1126/science.aay0479

Direct synthesis of adipic acid esters via palladium-catalyzed carbonylation of 1,3-dienes.

The direct carbonylation of 1,3-butadiene offers the potential for a more cost-efficient and environmentally benign route to industrially important adipic acid derivatives. However, owing to the complex reaction network of regioisomeric carbonylation and isomerization pathways, a selective practical catalyst for this process has thus far proven elusive. Here, we report the design of a pyridyl-substituted bidentate phosphine ligand (HeMaRaphos) that, upon coordination to palladium, catalyzes adipate diester formation from 1,3-butadiene, carbon monoxide, and butanol with 97% selectivity and 100% atom-economy under industrially viable and scalable conditions (turnover number > 60,000). This catalyst system also affords access to a variety of other di- and triesters from 1,2- and 1,3-dienes.

Negative Photochromism and Luminescent Properties of Amphiphilic Spiropyran in Solutions and at the Interface

The work presents the results of a study of the negative photochromism and luminescent properties of 1',3'-dihydro-3',3'-dimethyl-6-nitro-1'-octadecyl-[1-benzopyran-2,2'-indole]-8-methyl pyridinium chloride (SP2) in solutions, Langmuir monolayers, and cast films. It has been demonstrated that the introduction of the pyridine substituent into the chromene part of the amphiphilic spiropyran leads to stabilization of the open form of the compound under dark conditions, both in the dissolved and in the ordered planar state. The kinetic characteristics of photoreactions occurring in organic solvents upon irradiation by visible light and during relaxation in darkness are determined. Negative solvatochromism of SP2, which consists in the hypsochromic shift of the maximum absorption of the merocyanine form of the compound upon increase of the solvent polarity, is revealed. The luminescent properties of solutions of negative spiropyran and its cast films are investigated. For the first time, SP2 monolayers are formed at the air/water interface and their properties are studied. It is established that SP2 retains its photochromic properties upon transition from solutions to a two-dimensional condensed state. The results obtained open up broad prospects for the development of switchable optoelectronic and information systems based on negative spiropyrans.

Red/Near‐Infrared Thermally Activated Delayed Fluorescence OLEDs with Near 100 % Internal Quantum Efficiency

AbstractDeveloping red thermally activated delayed fluorescence (TADF) emitters, attainable for both high‐efficient red organic light‐emitting diodes (OLEDs) and non‐doped deep red/near‐infrared (NIR) OLEDs, is challenging. Now, two red emitters, BPPZ‐PXZ and mDPBPZ‐PXZ, with twisted donor–acceptor structures were designed and synthesized to study molecular design strategies of high‐efficiency red TADF emitters. BPPZ‐PXZ employs the strictest molecular restrictions to suppress energy loss and realizes red emission with a photoluminescence quantum yield (ΦPL) of 100±0.8 % and external quantum efficiency (EQE) of 25.2 % in a doped OLED. Its non‐doped OLED has an EQE of 2.5 % owing to unavoidable intermolecular π–π interactions. mDPBPZ‐PXZ releases two pyridine substituents from its fused acceptor moiety. Although mDPBPZ‐PXZ realizes a lower EQE of 21.7 % in the doped OLED, its non‐doped device shows a superior EQE of 5.2 % with a deep red/NIR emission at peak of 680 nm.

Synthesis, structural/photophysical characterization and theoretical investigations with new β-pyridinium/quinolinium and β-bromine substituted bis(1,3-dimethylbarbituric acid) trimethine oxonol dyes that display large Stokes shifts

An efficient 3-step procedure for the synthesis of novel β-pyridinium/quinolinium/bromine-substituted bis(1,3-dimethylbarbituric acid)trimethine oxonol dyes was developed that involves a simple triethylamine-promoted condensation of 1,3-dimethylbarbituric acid with preformed vinamidinium salts. 1H NMR, 13C NMR, IR and mass spectral data confirmed the structures of the dyes. Solutions of the dyes in CH3CN exhibited absorption and fluorescence emission maxima in the range of 467–480 nm and 531–712 nm, respectively, identifying that the dyes show unusually large Stokes shifts (~230 nm). Investigating the photophysical properties of dye 3a in a series of organic solvents with different polarity confirmed intramolecular charge transfer (ICT). Optimized geometries of the synthesized dyes in the ground state calculated using density functional theory (DFT) at the B3LYP/6-311G(d,p) theory level identified that planar cis and trans configurations were preferred for the pyridinium/quinolinium and bromine substituted dyes, respectively. TD-DFT calculations on the dye excited state structures identified that rotation of the bulky pyridinium substituents during relaxation is responsible for the large Stokes shift. The unique properties of the dyes suggest they could find use as fluorescent visualizers for intracellular imaging.

Crystal structure of (15,20-bis-(2,3,4,5,6-penta-fluoro-phen-yl)-5,10-{(pyridine-3,5-di-yl)bis-[(sulfane-diyl-methyl-ene)[1,1'-biphen-yl]-4',2-di-yl]}porph-yrin-ato)nickel(II) di-chloro-methane x-solvate (x > 1/2) showing a rare CN5 coordination.

The crystal structure of the title compound, [Ni(C63H31F10N5S2)]·xCH2Cl2 (x > 1/2), consists of Ni-porphyrin complexes that are located in general positions and di-chloro-methane solvent mol-ecules that are disordered around centers of inversion. The NiII ions are in a square-pyramidal (CN5) coordination, with four porphyrin N atoms in the equatorial and a pyridine N atom in the apical position and are shifted out of the porphyrine N4 plane towards the coordinating pyridine N atom. The pyridine substituent is not exactly perpendicular to the N4 plane with an angle of inter-section between the planes planes of 80.48 (6)°. The di-chloro-methane solvent mol-ecules are hydrogen bonded to one of the four porphyrine N atoms. Two complexes are linked into dimers by two symmetry-equivalent C-H⋯S hydrogen bonds. These dimers are closely packed, leading to cavities in which additional di-chloro-methane solvent mol-ecules are embedded. These solvent mol-ecules are disordered and because no reasonable split model was found, the data were corrected for disordered solvent using the PLATON SQUEEZE routine [Spek (2015 ▸). Acta Cryst. C71, 9-18].

Experimental and Theoretical Approaches in the Study of Phenanthroline-Tetrahydroquinolines for Alzheimer's Disease.

The imino‐Diels‐Alder reaction is one of the most common strategies in organic chemistry and is an important tool for providing a broad spectrum of biologically active heterocyclic systems. A combined theoretical and experimental study of the imino‐Diels‐Alder reaction is described. The new phenanthroline‐tetrahydroquinolines were evaluated as cholinesterase inhibitors. Their cytotoxicity in human neuroblastoma SH‐SY5Y cells was also evaluated. The theoretical results suggest that compounds formation in stages can be explained by endo cycloadducts under the established reaction conditions, thereby confirming experimental results obtained for percentage yield. These results allowed us to establish that pyridine substituent remarkably influences activation energy and reaction yield, as well as in acetylcholinesterase (AChE) activity. Among these derivatives, compounds with 4‐pyridyl and 4‐nitrophenyl showed favorable AChE activity and proved to be non‐cytotoxic.

Hydrogen Transfer Activation via Stabilization of Coordinatively Vacant Sites: Tuning Long-Range π-System Electronic Interaction between Ru(0) and NHC Pendants

The insertion of a pyridine substituent on the lateral chain of N-heterocyclic carbene ligands enhances the catalytic activity of [Ru(CO)2(cyclopentadienone)(NHC)] complexes, precursors of Shvo-typ...

Effect of pyridine and pyridine with substituent on photoluminescence of nanoparticles CdS prepared by liquid –liquid interface reaction

Liquid – liquid interface reaction is the method forpreparation nanoparticles (NP'S) which depend on the supersaturation of ions that provide by using the system that consist fromtoluene and water, the first one is above the second to obtainnanoparticles (NP's) CdS at the interface separated between thesetwo immiscible liquid. The structure properties were characterized byXRD-diffraction and transmission electron microscopy.The crystalline size estimate from X-ray diffraction patternusing Scherer equation to be about 7nm,and by TEM analysis give usthat ananosize is about 5 nm which give a strong comparable withBohr radius. Photoluminescence analysis give two emission peak,the first one around the 380 nm and the second around the 760nmwhich indicate to the band edge and surface defect emissionrespectively and the intensity of these emission change with thechange of the pyridine substituent.

Synthesis, crystal structure, self-assembly of C60 derivatives bearing rigid pyridine substituents.

Microstructures of fullerene derivatives formed via self-assembly strategy facilitate the versatile applications of these zero-dimensional molecules. However, the accurate elucidation of formation mechanism of fullerene microstructures is a challenge issue. A novel fullerene derivative 2 with rigid pyridine substituent was synthesized and characterized by X-ray crystallography. Using the strategy of liquid–liquid interfacial precipitation, self-assembly of 2 affords a micrometer-sized flowerlike and a discoid morphology. Based on the crystal packing of 2, the proper formation mechanism of different morphologies was proposed. Meanwhile, the photoelectrochemical properties of different morphologies of 2 was also unveiled.

Photoinduced Intramolecular Charge Transfer and Hyperpolarizability Coefficient in Push-Pull Pyridinium Salts with Increasing Strength of the Acceptor Group.

The synthesis of three push-pull cationic dyes is reported here together with a photophysical study carried out by stationary and ultrafast spectroscopies. The hyperpolarizability (β) values of the three molecules have been estimated through a simple solvatochromic method based on conventional, low-cost equipment, which had been tested previously with success in our laboratory. The investigated pyridinium salts showing strong negative solvatochromism bear the same piperidine ring as a strong electron-donor group and the same thiophenes as electron-rich π-linkers, but differ in terms of the N-substituent on the electron-acceptor pyridinium unit, namely N-methyl in compound A, N-pyrimidin-2yl in B and N-2,4-dinitrophenyl in C. The derived β values were found to increase (in the order A<B<C) along with the increasing electron-acceptor strength of the pyridinium substituent, with the highest polarizability being estimated for the derivative bearing the strongest electron-withdrawing substituent dinitrobenzene. State-of-the-art femtosecond transient absorption measurements evidenced fast kinetics and dynamics in the singlet excited state in agreement with charge transfer (CT) processes promoted by excitation, with a proper ICT state observed in the case of C. This finding confirms the efficiency of photoinduced intramolecular CT as a significant factor that affects the NLO response.

Structural Insight into Enantioselective Inversion of an Alcohol Dehydrogenase Reveals a "Polar Gate" in Stereorecognition of Diaryl Ketones.

Diaryl ketones are important building blocks for synthesizing pharmaceuticals and are generally regarded as "difficult-to-reduce" ketones due to the large steric hindrance of their two bulky aromatic side chains. Alcohol dehydrogenase from Kluyveromyces polyspora ( KpADH) has been identified as a robust biocatalyst due to its high conversion of diaryl ketone substrate (4-chlorophenyl)(pyridine-2-yl)ketone (CPMK) with a moderate R-selectivity of 82% ee. To modulate the stereoselectivity of KpADH, a "polarity scanning" strategy was proposed, in which six key residues inside and at the entrance of the substrate binding pocket were identified. After iterative combinatorial mutagenesis, variants Mu-R2 and Mu-S5 with enhanced (99.2% ee, R) and inverted (97.8% ee, S) stereoselectivity were obtained. The crystal structures of KpADH and two mutants in complex with NADPH were resolved to elucidate the evolution of enantioselective inversion. Based on MD simulation, Mu-R2-CPMKProR and Mu-S5-CPMKProS were more favorable in the formation of prereaction states. Interestingly, a quadrilateral plane formed by α-carbons of four residues (N136, V161, C237, and G214) was identified at the entrance of the substrate binding pocket of Mu-S5; this plane acts as a "polar gate" for substrates. Due to the discrepancy in charge characteristics between chlorophenyl and pyridine substituents, the pro- S orientation of CPMK is defined when it passes through the "polar gate" in Mu-S5, whereas the similar plane in wild-type is blocked by several aromatic residues. Our result paves the way for engineering stereocomplementary ADH toward bulky diaryl ketones and provides structural insight into the mechanism of stereoselective inversion.

Design, synthesis and characterization of new trimethine oxonol dyes from 1,3-indandione and 2-substituted vinamidinium salts

A series of novel cationic trimethine oxonol dyes with pyridinium substituents in the β-position of polymethine chain have been synthesized via an easy and efficient methodology by the condensation of 1,3-indandione with various substituted vinamidinium salts in ethanol as a green solvent without formation of any byproducts. The chemical structure of the synthesized dyes was investigated by FTIR, 1H NMR, 13C NMR, and HRMS techniques. The solutions of the new dyes in DMF absorbed visible light wavelengths at about 524–530 nm with narrow band widths and high molar absorption coefficients (around 1–2 × 105 dm3 mol−1 cm−1). They also exhibited fluorescence with a maximum emission intensity at about 700 nm and a relatively large (about 171–176 nm) Stokes shift. An optimized geometrical configuration of the dyes has been determined by using the density functional theory (DFT) at B3LYP/6-311G(d,p) theoretical level.

Selective Palladium-Catalyzed Carbonylation of Alkynes: An Atom-Economic Synthesis of 1,4-Dicarboxylic Acid Diesters.

A class of novel diphosphine ligands bearing pyridine substituents was designed and synthesized for the first time. The resulting palladium complexes of L1 allow for chemo- and regioselective dialkoxycarbonylation of various aromatic and aliphatic alkynes affording a wide range of 1,4-dicarboxylic acid diesters in high yields and selectivities. Kinetic studies suggest the generation of 1,4-dicarboxylic acid diesters via cascade hydroesterification of the corresponding alkynes. Based on these investigations, the chemo- and regioselectivities of alkyne carbonylations can be controlled as shown by switching the ligand from L1 to L3 or L9 to give α,β-unsaturated esters.

Poly(N-bromo-2-ethynylpyridinium bromide) for quasi-solid state dye-sensitized solar cell applications

ABSTRACTA new conjugated ionic polymer, poly(N-bromo-2-ethynylpyridinium bromide) (PBEPB) was applied for a quasi-solid-state dye-sensitized solar cells (DSSCs) and compared the device performance with poly(N-bromo-2-ethynylpyridinium iodide) (PBEPI) as reference cell. The polymer was prepared by the spontaneous polymerization of 2-ethynylpyridine using bromine. The PBEPB was completely soluble in such organic solvents as DMF, DMSO and NMP etc. The photoluminescence peaks of PBEPB was observed at 407 nm and 516 nm, which corresponds to the photon energy of 3.15 eV and 2.41 eV, respectively. Quasi-solid-state DSSCs with a SnO2:F/TiO2/D719 dye/solid-state electrolyte/Pt device was fabricated with an ionic conjugated polymer with pyridinium substituents, which shows the power conversion efficiency (PCE) of 5.95%.

Static and dynamic coordination behaviours of copper(i) ions in hexa(2-pyridyl)benzene ligand systems.

Two hexaarylbenzenes having six pyridine substituents (LH and LM) were prepared and six corresponding coordination complexes with copper(i) chloride were synthesized. Monomeric complexes (1, 2a and 2b) and 1D coordination polymers (3, 4 and 5) were synthesized via the judicious concentration control of copper(i) ions and characterized fully by X-ray crystal analysis. The binding modes of the ligands to copper(i) ions in the coordination polymers were dependent on steric effects and solvents to determine the morphology of the coordination polymers. More interestingly, dynamic behaviours of the monomeric complexes (1, 2a and 2b) in the solution phase were studied to show potential applications of molecular machines with fluxional motions.

Syntheses, Crystal Structures, and Properties of Two d10 Metal Complexes Based on Ferrocenyl Ligands Bearing Pyrazolyl Pyridine Substituents

Two new complexes, namely, [Cd2(L1)2(NCS)4(DMF)2] · 4H2O (I) and {[Zn3(L2)4(SO4)3(H2O)8] · 3DMF · 6H2O} n (II) have been synthesized through self-assembly of Cd(II) or Zn(II) salts with ferrocenyl ligands bearing pyrazolyl pyridine substituents. The two compounds were characterized by IR spectra, element analysis, X-ray powder diffraction, single-crystal X-ray diffraction (СIF files CCDC nos. 949526 (I), 949527 (II)), and thermogravimetric analysis. Complex I crystallizes in the monocline space group P21/c and exhibits a discrete dinuclear structure. The adjacent dinuclear molecules are packed into a 1D linear chain through the hydrogen-bond interactions. Complex II is a neutral one-dimensional infinite zigzag coordination chain. The 3D packing diagram of II contains two types of voids and the solvated DMF and water molecules filled them and stabilized by the hydrogen bonds. In addition, the redox properties of both complexes I and II have also been investigated.

Substitution of the laser borane anti-B18H22 with pyridine: a structural and photophysical study of some unusually structured macropolyhedral boron hydrides.

Reaction of anti-B18H221 with pyridine in neutral solvents gives sparingly soluble B16H18-3',8'-Py23a as the major product (ca. 53%) and B18H20-6',9'-Py22 (ca. 15%) as the minor product, with small quantities of B18H20-8'-Py 4 (ca. 1%) also being formed. The three new compounds 2, 3a and 4 are characterized by single-crystal X-ray diffraction analyses and by multinuclear multiple-resonance NMR spectroscopy. Compound 2 is of ten-vertex nido:ten-vertex arachno two-atoms-in-common architecture, long postulated for a species with borons-only cluster constitution, but previously elusive. Compound 3a is of unprecedented ten-vertex nido:eight-vertex arachno two-atoms-in-common architecture. The single-crystal X-ray diffraction analysis for the picoline derivative B16H18(NC5H4Me)23b, similarly obtained, is also presented. B18H20Py 4 is also previously unreported but is of known ten-vertex nido:ten-vertex nido two-atoms-in-common architecture of anti configuration, but now with the pyridine ligand positioned differently to other reported examples of B18H20L compounds. Factors behind the remarkably low solubility of 3a and 3b are elucidated in terms of electrostatic potential (ESP) calculations, polarity, and van der Waals complementarities. In view of contemporary developing high interest in the fluorescent properties of macropolyhedral boron-containing species, a detailed assessment of the photophysical characteristics of 3a and 4 is also presented. In contrast to the thermochromic fluorescence of 2 (from 620 nm brick-red at room temperature to 585 nm yellow at 8 K, quantum yield 0.15), compound 3a is only weakly phosphorescent in the yellow region (590 nm, quantum yield 0.01), whereas compound 4 exhibits no luminescence. The far more photoactive nature of compound 2 is associated with S1 excited-state minima structures that differ from each other only by the relative rotational positions of the pyridine substituents on its disubstituted ten-vertex {arachno-B10Py2}-subcluster. The wavelength and relative intensity of fluorescence from these structures depends on the rotational positions of the pyridine ligands, which in turn are influenced by temperature and/or rotational inhibition in the solid-state.

Effect of the Pyridine Substituent on the Role of the Phenol Functional Group in [Cu(pOHBz)2(dPy)2] Complexes (pOHBz: p‐Hydroxybenzoate, dPy= 4‐Phenylpyridine, 4‐Benzylpyridine, 3‐Phenylpyridine).

AbstractThe crystal structure of three new complexes of stoichiometry [Cu(pOHBz)2(dPy)2] (pOHBz: p‐hydroxybenzoate, dPy= 4‐phenylpyridine, 4‐benzylpyridine, 3‐phenylpyridine) and its comparison with the previously reported [Cu(pOHBz)2(Py)2] (1) indicate that the nature and position of the pyridine substituent determines different roles for the phenol group from the pOHBz ligand and, consequently, the coordination number and geometry of Cu(II) centers. Results herein reported show the versatility of the pOHBz ligand towards the coordination of Cu(II). Different carboxylate bonding modes are also observed: monodentate, bidentate chelating or bidentate bridge. Besides, this governs the different roles of the phenol group of the pOHBz ligand: founding of supramolecular hydrogen‐bond based network or direct bonding to the copper cation, yielding 2D coordination polymers.