Pyridyl Moiety Research Articles

Syntheses and crystal structures of coordination polymers of a porphyrin ligand bearing two pyridyl and two carboxyl moieties

In this work, we designed and synthesized a porphyrin-based ligand, 5,15-bis(4-carboxyphenyl)-10,20-dipyridyl porphyrin, DCDPP (H4L), which bears two carboxyl and two pyridyl moieties. Coordination of Mn(II) and Zn(II) acetates with DCDPP afforded two novel coordination polymers, [MnHL]n (1) and [ZnH2L]n·nCH3COOH (2), respectively. Single crystal X-ray diffraction analyses revealed that complex 1 exhibits 2D coordination networks, which are further linked through hydrogen bonds to form a 3D network structure. In complex 2, 1D zigzag coordination chains were generated and further linked through hydrogen bonds to form a 2D structure. Interestingly, the carboxyl moieties in these complexes are noncoordinated, and the pyridyl moieties are either coordinated or noncoordinated, and the noncoordinated carboxyl and pyridyl moieties are involved in intermolecular hydrogen bonds, which are favorable for forming the hydrogen-bonded networks.

ChemInform Abstract: One‐Pot Synthesis and Applications of N‐Heteroaryl Iodonium Salts.

An efficient one-pot synthesis of N-heteroaryl iodonium triflates from the corresponding N-heteroaryl iodide and arene has been developed. The reaction conditions resemble our previous one-pot syntheses, with suitable modifications to allow N-heteroaryl groups. The reaction time is only 30 min, and no anion exchange is required. The obtained iodonium salts were isolated in a protonated form, these salts can either be employed directly in applications or be deprotonated prior to use. The aryl groups were chosen to induce chemoselective transfer of the heteroaryl moiety to various nucleophiles. The reactivity and chemoselectivity of these iodonium salts were demonstrated by selectively introducing a pyridyl moiety onto both oxygen and carbon nucleophiles in good yields.

Optoelectronic properties and structural effects of the incremental addition of pyridyl moieties on a rhodium dimer.

The synthesis and characterization of five C-C coupling products obtained from the reaction of a paddlewheel tetrakis 4-bromo-N,N'-diphenylbenzamidinate dirhodium dimer with 4-pyridineboronic acid pinacol ester are reported. The coupling reactions occur on one to four amidinate ligands, leading to rhodium dimers containing [tetrakis, tris, cis-bis, trans-bis, or mono]-N,N'-diphenyl-4-(pyridin-4-yl)benzamidinate ligands, effectively creating new binding sites on the metal complexes. The new compounds were isolated by column chromatography, and the exact conformations were verified by X-ray crystallography. Redox processes showed only a small variation within the coupling products and included two oxidations (1.30 ± 0.02 V, 0.27 ± 0.01 V vs SCE) and one reduction (-1.55 ± 0.02 V vs SCE), all centered on the Rh-Rh core. Time-dependent density functional theory (TD-DFT) was used to analyze this series with four other fully characterized N,N'-diphenyl-aryl-amidinate rhodium dimers that were found in the literature. The two main absorption bands of these nine rhodium dimers were compared to TD-DFT calculations, both giving excellent correlation. The first, a metal-to-metal (MM) transition around 11800 cm(-1) (845 nm) was blue-shifted in the calculation, with an average difference of 1378 cm(-1) but had only a 15 cm(-1) standard deviation, showing a strong correlation despite the energy difference. The second, a metal-to-ligand charge transfer (MLCT) transition around 18900 cm(-1) (530 nm) was a near perfect match with only a 64 cm(-1) average difference and a 35 cm(-1) standard deviation. The electronic transition, redox potentials, and HOMO and LUMO energies of all dimers were plotted versus the Hammett parameter (σ) of the aryl group and Taft's model with 2 components: field effects (σF) and resonance (σR). The properties involving only the Rh-Rh core (MM band, all oxidation potentials, HOMO and LUMO) were fit with a single set of σF and σR contributions (73% and 27%), with a goodness-of-fit (R(2)) value ranging from 90% to 99.7%. The metal-dimer to ligand charge-transfer band, involving the amidinate ligand, displayed different values of contribution with 45% and 55% for the σF and σR, respectively, with a fit of 94.8%. The accuracy of these fits enables the designed modification of amidinate-based dirhodium complexes to achieve desirable redox and spectroscopic properties.

Remarkable shape-sustaining, load-bearing, and self-healing properties displayed by a supramolecular gel derived from a bis-pyridyl-bis-amide of L-phenyl alanine.

A series of bis-amides decorated with pyridyl and phenyl moieties derived from L-amino acids having an innocent side chain (L-alanine and L-phenyl alanine) were synthesized as potential low-molecular-weight gelators (LMWGs). Both protic and aprotic solvents were found to be gelled by most of the bis-amides with moderate to excellent gelation efficiency (minimum gelator concentration=0.32-4.0 wt.% and gel-sol dissociation temperature T(gel)=52-110 °C). The gels were characterized by rheology, DSC, SEM, TEM, and temperature-variable (1)H NMR measurements. pH-dependent gelation studies revealed that the pyridyl moieties took part in gelation. Structure-property correlation was attempted using single-crystal X-ray and powder X-ray diffraction data. Remarkably, one of the bis-pyridyl bis-amide gelators, namely 3,3-Phe (3-pyridyl bis-amide of L-phenylalanine) displayed outstanding shape-sustaining, load-bearing, and self-healing properties.

ChemInform Abstract: Synthesis of Heteroaryl Compounds Through Cross‐Coupling Reaction of Aryl Bromides or Benzyl Halides with Thienyl and Pyridyl Aluminum Reagents.

AbstractAn efficient method for synthesis of useful biaryl building blocks containing thienyl or pyridyl moieties is provided through cross‐coupling reactions of freshly prepared heteroaryl aluminum reagents with aryl bromides or benzyl halides.

Hybrid fluorescent nanoparticles fabricated from pyridine-functionalized polyfluorene-based conjugated polymer as reversible pH probes over a broad range of acidity-alkalinity

Conjugated polymer nanoparticles (CPNs) were developed based on a polyfluorene-based conjugated polymer with thiophene units carrying pyridyl moieties incorporated in the backbone of polymer chains (PFPyT). Hybrid CPNs fabricated from PFPyT and an amphiphilic polymer (NP1) displayed pH-sensitive fluorescence emission features in the range from pH 4.8 to 13, which makes them an attractive nanomaterial for wide range optical sensing of pH values. The fluorescence of hybrid CPNs based on chemically close polyfluorene derivatives without pyridyl moieties (NP3), in contrast, remains virtually unperturbed by pH values in the same range. The fluorescence emission features of NP1 underwent fully reversible changes upon alternating acidification/basification of aqueous dispersions of the CPNs and also displayed excellent repeatability. The observed pH sensing properties of NP1 are attributed to protonation/deprotonation of the nitrogen atoms of the pyridine moieties. This, in turn, leads to the redistribution of electron density of pyridine moieties and their participation in the π-conjugation within the polymer main chains. The optically transparent amphiphilic polymers also exerted significant influence on the pH sensing features of the CPNs, likely by acting as proton sponge and/or acid chaperone.

Preparation and Characterization of a Halogen-Bonded Shape-Persistent Chiral Alleno-acetylenic Inclusion Complex

A chiral bidentate inclusion complex has been formed by halogen-bond interaction between the pyridyl moieties of a pyridoallenoacetylenic host and octafluorodiiodobutane. X-ray crystallography showed that the guest adopts a chiral conformation inside the molecular channels formed by stacking of the host units. A 10 ppm shielding of the (15)N NMR resonance for the pyridil units provided evidence of the formation of the halogen-bond complex in solution.

One‐Pot Synthesis and Applications of N‐Heteroaryl Iodonium Salts

An efficient one-pot synthesis of N-heteroaryl iodonium triflates from the corresponding N-heteroaryl iodide and arene has been developed. The reaction conditions resemble our previous one-pot syntheses, with suitable modifications to allow N-heteroaryl groups. The reaction time is only 30 min, and no anion exchange is required. The obtained iodonium salts were isolated in a protonated form, these salts can either be employed directly in applications or be deprotonated prior to use. The aryl groups were chosen to induce chemoselective transfer of the heteroaryl moiety to various nucleophiles. The reactivity and chemoselectivity of these iodonium salts were demonstrated by selectively introducing a pyridyl moiety onto both oxygen and carbon nucleophiles in good yields.

Magnetically Recoverable Catalysts Based on Polyphenylenepyridyl Dendrons and Dendrimers

Here, a systematic study of magnetite nanoparticle (NP) formation in the presence of functional polyphenylenepyridyl dendrons and dendrimers of different generations and structures (such as focal groups, periphery and a combination of phenylene and pyridyl moieties) has been reported. For certain dendron/dendrimer concentrations and structures, well-dispersible, multi-core, flower-like crystals are formed which display ferrimagnetic-like behavior. It is noteworthy that the least complex second generation polyphenylenepyridyl dendrons with a carboxyl focal group already allow formation of flower-like crystals. Magnetically recoverable catalysts were obtained via Pd NP formation in the dendron/dendrimer shells of magnetite NP and tested in selective hydrogenation of dimethylethynylcarbinol to dimethylvinylcarbinol. Dependences of catalytic activity and selectivity on the dendron/dendrimer generation and structure, type of Pd species, and Pd NP size have been demonstrated. High selectivity and activity of these catalysts along with easy catalyst recovery and successful repeated use make them promising in catalytic hydrogenation.

Rhodium Amidinate Dimers as Structural and Functional Hubs for Multimetallic Assemblies

The synthesis and characterization of multichromophore assemblies based on a dirhodium tetra-N,N'-diphenylisonicotinamidinate dimer are reported. The pyridyl moieties were used to coordinate up to four positively charged rhenium(I) chromophores of the form fac-[Re(bpy)(CO)3L]PF6 (bpy = 2,2'-bipyridine, L = a pyridyl group on the Rh2 dimer). The mono-, bis-, tris-, and tetrarhenium assemblies were isolated by size-exclusion chromatography, and their spectroscopic and electrochemical properties were studied and compared with DFT and time-dependent (TD) DFT models of the original rhodium dimer and the mono- and tetrarhenium assembly. The rhenium chromophores modify the properties of the rhodium dimer: for example, the first oxidation of the Rh2 dimer (Rh-Rh δ* orbital) increased from the original 210 mV versus SCE in acetonitrile, by 45 mV per rhenium complex added, finishing at 390 mV for the tetrarhenium complex. The rhodium dimers display solvatochromism with acetonitrile (MeCN) due to the formation of an axial adduct and has an association constant that increased by a factor of 3.8 when the dimer has four rhenium chromophores. The absorption data clearly exhibited the cumulative effect of the addition of rhenium chromophores in the 230 to 400 nm range. The main visible band, a metal-dimer-to-ligand charge transfer ((1)M2LCT) transition determined by TD-DFT, red-shifts from 541 nm to 603 nm, while the main near-IR band, a (1)Rh2(π*→σ*) transition, has a small blue-shift (∼26 cm(-1)/Re), varying from 837 to 831 nm upon addition of the four Re(I) chromophores. This was observed in TD-DFT also with a total shift of 105 cm(-1) for the tetrarhenium assembly. In terms of emission, the rhenium excited state was completely quenched upon coordination to the dimer, suggesting fast electron transfer of the rhodium dimer. All other aspects of the rhenium chromophore are similar to the parent complex where L = pyridine, showing similar redox couples and additive spectral characteristics.

Synthesis of N-picolylcarboxamides via palladium-catalysed aminocarbonylation of iodobenzene and iodoalkenes

A systematic investigation of the palladium-catalysed aminocarbonylation of iodobenzene, 1-iodocyclohexene and 1′-iodostyrene in the presence of N-nucleophiles containing pyridyl moieties (2-, 3- and 4-picolylamine, N-ethyl-4-picolylamine, di-(2-picolyl)amine) was carried out. The two types of iodo substrates differ substantially regarding the selectivity towards carbonylation: while the aminocarbonylation of iodobenzene resulted in the formation of carboxamide and ketocarboxamide mixtures under various conditions, with the predominant formation of ketocarboxamide even at low carbon monoxide pressure, the aminocarbonylation of iodoalkenes under same conditions gave the corresponding unsaturated carboxamide exclusively. Most of the carboxamides and phenylglyoxylamides, obtained via single and double carbon monoxide insertion, respectively, were isolated in yields of synthetic interest (up to 86%). Low reaction rates and unexpected chemoselectivity towards carboxamide formation have been observed with di-(2-picolyl)amine as N-nucleophile in the aminocarbonylation of iodobenzene.

Synthesis, characterization and electrochemical recognition of metal ions of three new ferrocenyl derivatives containing pyridyl moiety

Three new ferrocene (Fc) based receptors with pyridyl moiety, named methyl-6-ferrocenoylacetyl-2-pyridine carboxylate (FcL1), 1,1′-(2,6-bispyridyl)bis-3-ferrocenyl-1,3-propanedione (FcL2), ferrocenecarboxaldehyde-2,6-dipicolinoyhydrazone (FcL3) were synthesized, and further characterized by elemental analysis, IR spectra, UV-Vis spectra, 1H and 13C NMR. The electrochemical properties and ion sensing properties of FcL1, FcL2 and FcL3 were also investigated by means of cyclic voltammetry in ethanol solution with 0.1 mol/L LiClO4 as the supporting electrolyte. The E0 values of the receptors increase with the scanning rate increasing at high scanning rate, and Ipa/Ipc approaches unity, indicating that the redox reaction is basically reversible. Their recognition performances to different metal cations such as Cd(II), Co(II), Cu(II), Hg(II), Mn(II), Ni(II), Zn(II) show that the FcL1 is responsive to Cu(II) with the maximum electrochemical shift of the FcL1 for Cu(II) of about 72.0 mV, whereas the FcL2 is responsive to Cu(II) and Mn(II) with shift of 102 mV and 109 mV, respectively, and the FcL3 is responsive to Hg(II) and Mn(II) with the shift of 53.0 mV and 54.0 mV, respectively. All the results show that these receptors may have potential applications in electrochemical sensor technology, material science, and molecular devices.

Efficient Electronic Communication of Two Ruthenium Centers through a Rigid Ditopic N‐Heterocyclic Carbene Linker

A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co-planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L4Ru-C,N-bbi-C,N-RuL4] were obtained by a transmetalation methodology (C,N-bbi-C,N=benzobis(N-pyridyl-N'-methyl-imidazolylidene). The two metal centers are electronically decoupled when the ruthenium is in a pseudotetrahedral geometry imparted by a cymene spectator ligand (L4=[(cym)Cl]). Ligand exchange of the Cl(-)/cymene ligands for two bipyridine or four MeCN ligands induced a change of the coordination geometry to octahedral. As a consequence, the ruthenium centers, separated through space by more than 10 Å, become electronically coupled, which is evidenced by two distinctly different metal-centered oxidation processes that are separated by 134 mV (L4=[(bpy)2]; bpy=2,2'-bipyridine) and 244 mV (L4=[(MeCN)4]), respectively. Hush analysis of the intervalence charge-transfer bands in the mixed-valent species indicates substantial valence delocalization in both complexes (delocalization parameter Γ=0.41 and 0.37 in the bpy and MeCN complexes, respectively). Spectroelectrochemical measurements further indicated that the mixed-valent Ru(II)/Ru(III) species and the fully oxidized Ru(III)/Ru(III) complexes gradually decompose when bound to MeCN ligands, whereas the bpy spectators significantly enhance the stability. These results demonstrate the efficiency of carbenes and, in particular, of the bbi ligand scaffold for mediating electron transfer and for the fabrication of molecular redox switches. Moreover, the relevance of spectator ligands is emphasized for tailoring the degree of electronic communication through the benzobis(carbene) linker.

Synthesis and Antimicrobial Activity of New Pyrimidine-Hydrazones

The synthesis of twelve new pyrimidine hydrazone derivatives and subsequent evaluation of their antimicrobial activities were the aims of this present work. The intermediate product 2-((pyrimidin-2-yl)thio)acetohydrazide was re- fluxed with different aromatic aldehydes/ketones in ethanol to yield N'-(arylidene)-2-((pyrimidine-5-yl)thio)- acetohydrazide derivatives (3a-l). The structures of the compounds were elucidated by NMR, FTIR, MS, and elemental analyses. Additionally the final compounds (3a-l) were evaluated for their antimicrobial activity using a microdilution method against a panel of pathogenic Gram positive, Gram negative, and fungus strains, i.e. Escherichia coli, Pseudo- monas aeruginosa, Salmonella typhimurium, Bacillus cereus, Bacillus subtilis, Serrratia marcescens, Staphylococcus epi- dermidis, and Candida utilis. Compound N'-(2-pyrilidene)-2-((pyrimidine-5-yl)thio)acetohydrazide (3a) possessing a 2- pyridyl moiety was found to be the most active (MIC= 31.25-250 �g/mL) derivative toward the tested microorganisms.

Probing the Effects of Ligand Isomerism in Chiral Luminescent Lanthanide Supramolecular Self‐Assemblies: A Europium “Trinity Sliotar” Study

"Trinity Sliotar" family: Chiral ligands containing pyridyl and naphthalene moieties were synthesized and characterized. These ligands were successfully used for the synthesis of Eu(III) bundles where chirality of the ligand is successfully transferred onto the lanthanide centre resulting in circularly polarized red luminescence.

Protonation-Induced Chromism of Pyridylethynyl-Appended [core+exo]-Type Au8 Clusters. Resonance-Coupled Electronic Perturbation through π-Conjugated Group

A series of [core+exo]-type Au8 clusters bearing two alkynyl ligands on the exo gold atoms ([Au8(dppp)4(C≡CR)2](2+), 2-6) were synthesized by the reaction of [Au8(dppp)4](2+) (1) with alkynyl anions. Although the C≡C moieties directly attached to the Au8 units did not affect the optical properties arising from intracluster transitions, the pyridylethynyl-bearing clusters (4-6) exhibited reversible visible absorption and photoluminescence responses to protonation/deprotonation events of the terminal pyridyl moieties. The chromism behaviors and proton-binding constants of these clusters were highly dependent on the relative position of the pyridine nitrogen atom, such that the 2-pyridyl (4) and 4-pyridyl (6) isomers showed more pronounced responses than the 3-pyridyl isomer (5). These results suggest that the resonance-coupled movement of the positive charge upon protonation is involved in the optical responses, where the formation of extended charged resonance structures causes significant perturbation effects on the electronic properties of the Au8 unit and also contributes to the high binding affinities.

Novel triphenylamine-based cyclometalated platinum(II) complexes for efficient luminescent oxygen sensing

Novel triphenylamine-based cyclometalated Pt(II) complexes containing a pyridyl moiety have been synthesized and fully characterized. The cyclometalating ligands were prepared via an efficient palladium-catalyzed ligand-free Suzuki reaction of 4-(diphenylamino)phenylboronic acid with 2-pyridyl bromides under aerobic and aqueous conditions. The photophysical properties of the complexes exhibited that introducing an electron-withdrawing group like trifluoromethyl or cyano group on the 5-position of the pyridine ring affected the LUMO level of the Pt(II) complex significantly, resulting in a marked decrease in energy gap. Moreover, the complex with a cyano group at the 5-position imparts a substantial red-shift up to 56 nm. The O2 sensitivity of the complexes was quantitatively evaluated in a polymer film. The results of the O2-sensing sensitivity of the Pt(II) complexes demonstrated that the complex with a nitrile ligand exhibited the highest sensitivity (KSVapp = 0.102 Torr−1). The triphenylamine-based cyclometalated Pt(II) complexes are potential candidates for efficient luminescent oxygen sensing.

A Family of Porous Lonsdaleite-e Networks Obtained through Pillaring of Decorated Kagomé Lattice Sheets

A new and versatile class of metal-organic materials (MOMs) with augmented lonsdaleite-e (lon-e-a) topology is presented herein. This family of lon-e nets are built by pillaring of hexagonal two-dimensional kagomé (kag) lattices constructed from well-known [Zn2(CO2R)4] paddlewheel molecular building blocks (MBBs) connected by 1,3-benzenedicarboxylate (bdc(2-)) linkers. The pillars are [Cr3(μ3-O)(RCO2)]6 trigonal prismatic primary MBBs decorated by six pyridyl moieties (tp-PMBB-1). The three-fold symmetry (D3h) of tp-PMBB-1 is complementary with the alternating orientation of the axial sites of the paddlewheel MBBs and enables triple cross-linking of the kag layers by each pillar. These MOMs represent the first examples of axial-to-axial pillared undulating kag layers, and they are readily fine-tuned because the bdc(2-) moieties can be varied at their 5-position without changing the overall structure. This lon-e platform possesses functionalized hexagonal channels since the kag lattices are necessarily eclipsed. The effects of the substituent at the 5-positions of the bdc(2-) linkers upon gas adsorption, particularly the heats of adsorption of carbon dioxide and methane, were studied.

Polyphenylenepyridyl Dendrons with Functional Periphery and Focal Points: Syntheses and Applications

For the first time we report syntheses of a family of functional polyphenylenepyridyl dendrons with different generations and structures such as focal groups, periphery, and a combination of phenylene and pyridyl moieties in the dendron interior using a Diels–Alder approach and a divergent method. The dendron structure and composition were confirmed using NMR spectroscopy, MALDI-TOF mass spectrometry, FTIR, and elemental analysis. As a proof of concept that these dendrons can be successfully used for the development of nanocomposites, synthesis of iron oxide nanoparticles was carried out in the presence of thermally stable dendrons as capping molecules followed by formation of Pd NPs in the dendron shells. This resulted in magnetically recoverable catalysts exhibiting exceptional performance in selective hydrogenation of dimethylethynylcarbinol (DMEC) to dimethylvinylcarbinol (DMVC).

Synthesis and Fluoride Binding Properties of Tris-pyridinium Borane

A novel multi-cationic borane, tri-N-methylpyridinium substituted triarylborane, <TEX>$[BAr^N_3]I_3$</TEX> (<TEX>$[2]I_3$</TEX>) (<TEX>$Ar^N=4-(4-C_5H_4N-Me)-2,6-Me_2-C_6H_2$</TEX>) was prepared from the corresponding neutral tris-pyridyl borane, <TEX>$BAr_3$</TEX> (2a) (<TEX>$Ar=4-(4-C_5H_4N)-2,6-Me_2-C_6H_2$</TEX>). The crystal structure of 2a determined by X-ray diffraction study reveals the presence of tri-coordinate boron center with peripheral pyridyl moieties. The fluoride ion affinity of the cationic borane, <TEX>$[2]I_3$</TEX> was investigated by UV-vis absorption titrations and was compared with that of neutral 2a. While 2a binds fluoride with the binding constant of <TEX>$1.9{\times}10^2\;M^{-1}$</TEX> in <TEX>$THF/H_2O$</TEX> (9:1 v/v) mixture, <TEX>$[2]I_3$</TEX> shows a very high binding constant (<TEX>$K=1.0{\times}10^8\;M^{-1}$</TEX>) that is greater by six orders of magnitude than that of 2a in the same medium. This result indicates that the fluorophilicity of triarylborane can be drastically enhanced by multiple pyridinium substitutions.