Pyridine Adducts Research Articles

Enhancement of Second-Order Nonlinear Optical Properties of Centrosymmetric Ferrocenyl Borasiloxane by a Broken-Symmetry Approach

A new eight-membered centrosymmetric ferrocenyl borasiloxane FcBSi (1) and its pyridine adduct FcBSiPy (2) were synthesized and spectroscopically characterized. Further, the compound FcBSi (1) is c...

Experimental and Computational Studies on Quadruply Bonded Dimolybdenum Complexes with Terminal and Bridging Hydride Ligands.

This contribution focuses on complex [Mo2 (H)2 (μ-AdDipp2 )2 ] (1) and tetrahydrofuran and pyridine adducts [Mo2 (H)2 (μ-AdDipp2 )2 (L)2 ] (1⋅thf and 1⋅py), which contain a trans-(H)Mo≣Mo(H) core (AdDipp2 =HC(NDipp2 )2 ; Dipp=2,6-iPr2 C6 H3 ). Computational studies provide insights into the coordination and electronic characteristics of the central trans-Mo2 H2 unit of 1, with four-coordinate, fourteen-electron Mo atoms and ϵ-agostic interactions with Dipp methyl groups. Small size C- and N-donors give rise to related complexes 1⋅L but only one molecule of P-donors, for example, PMe3 , can bind to 1, causing one of the hydrides to form a three-centered, two-electron (3c-2e) Mo-H→Mo bond (2⋅PMe3 ). A DFT analysis of the terminal and bridging hydride coordination to the Mo≣Mo bond is also reported, along with reactivity studies of the Mo-H bonds of these complexes. Reactions investigated include oxidation of 1⋅thf by silver triflimidate, AgNTf2 , to afford a monohydride [Mo2 (μ-H)(μ-NTf2 )(μ-AdDipp2 )2 ] (4), with an O,O'-bridging triflimidate ligand.

Reactivity of O,N-heterocyclic germylene and stannylene towards μ-dithio-bis(tricarbonyliron)

Synthesis and single-crystal X-ray diffraction study (SC-XRD) of the O,N-heterocyclic germylene Ge(PhAp) (1) containing chelate 4,6-di-tert-butyl-N-phenyl-o-amidophenolate ligand (PhApH2, where Ap – o-amidophenolate) are reported. Germylene 1 demonstrates a monomeric structure in contrast to earlier known related stannylene Sn(PhAp) (2) existing as a dimer. Diverse weak intermolecular interactions (Ge…Ge, CH…π(chelate) and Ge…π(arene)) were detected in the crystal packing of germylene 1. Hirshfeld surface analysis has been performed to evaluate such interactions. Reactivity of compounds 1 and 2 towards dithiodiiron hexacarbonyl has been examined. Low-valent germanium(II) and tin(II) centers are readily inserted into S-S bond of dithiodiiron hexacarbonyl with the formation of Fe4(µ4-ES4)(CO)12 (E: Ge(3); Sn(4)) and bis-ligand complexes of tetravalent metals E(PhAp)2. The resulting germanium(IV) and tin(IV) bis-o-amidophenolates were isolated as six-coordinated pyridine adducts E(PhAp)2(Py)2 (E: Ge(5); Sn(6)). All complexes were characterized by SC-XRD.

From Pyridine Adduct of Borabenzene to (In)finite Graphene Architectures Functionalized with N → B Dative Bonds. Prototype Systems of Strong One- and Two-Photon Quantum Transitions Triggering Large Nonlinear Optical Responses

The synthesis and optoelectronics properties of polyaromatic hydrocarbons (PAHs) doped with boron and nitrogen units (BN) monopolize the interest of increasing numbers of researchers the past few y...

Ligand-Mediated Spin-State Changes in a Cobalt-Dipyrrin-Bisphenol Complex.

The influence of a redox-active ligand on spin-changing events induced by the coordination of exogenous donors is investigated within the cobalt complex [CoII(DPP·2–)], bearing a redox-active DPP2– ligand (DPP = dipyrrin-bis(o,p-di-tert-butylphenolato) with a pentafluorophenyl moiety on the meso-position. This square-planar complex was subjected to the coordination of tetrahydrofuran (THF), pyridine, tBuNH2, and AdNH2 (Ad = 1-adamantyl), and the resulting complexes were analyzed with a variety of experimental (X-ray diffraction, NMR, UV–visible, high-resolution mass spectrometry, superconducting quantum interference device, Evans’ method) and computational (density functional theory, NEVPT2-CASSCF) techniques to elucidate the respective structures, spin states, and orbital compositions of the corresponding octahedral bis-donor adducts, relative to [CoII(DPP·2–)]. This starting species is best described as an open-shell singlet complex containing a DPP·2– ligand radical that is antiferromagnetically coupled to a low-spin (S = 1/2) cobalt(II) center. The redox-active DPPn– ligand plays a crucial role in stabilizing this complex and in its facile conversion to the triplet THF adduct [CoII(DPP·2–)(THF)2] and closed-shell singlet pyridine and amine adducts [CoIII(DPP3–)(L)2] (L = py, tBuNH2, or AdNH2). Coordination of the weak donor THF to [CoII(DPP·2–)] changes the orbital overlap between the DPP·2– ligand radical π-orbitals and the cobalt(II) metalloradical d-orbitals, which results in a spin-flip to the triplet ground state without changing the oxidation states of the metal or DPP·2– ligand. In contrast, coordination of the stronger donors pyridine, tBuNH2, or AdNH2 induces metal-to-ligand single-electron transfer, resulting in the formation of low-spin (S = 0) cobalt(III) complexes [CoIII(DPP3–)(L)2] containing a fully reduced DPP3– ligand, thus explaining their closed-shell singlet electronic ground states.

Development of a reliable analytical method for the precise extractive spectrophotometric determination of cadmium(II) by using of chromogenic reagent: analysis of real samples

ABSTRACT A new analytical reagent N’’,N’’’-bis[(E)-(4-fluorophenyl)methylidene] thiocarbonohydrazide: bis-(4-fluoroPM)TCH was used for simple, fast and synergistic extractive spectrophotometric determination of cadmium(II). Cadmium(II) forms stable faint yellow coloured ternary complex at room temperature with reagent and pyridine as synergent having composition 1:2:2 (M:L:Py) at pH 4.0. The absorbance of coloured organic layer in iso amyl acetate is measured spectrophotometrically at 390 nm against reagent blank. In the extraction of cadmium(II), various affecting factors including the solution pH, reagent concentration, synergent concentration, equilibrium time, colour stability and effect of foreign ions are optimised. Beer’s law is obeyed in the concentration range 10–40 μg mL−1 of cadmium(II) and optimum range of 15–35 μg mL−1 of the metal as evaluated from Ringbom’s plot. Molar absorptivity and Sandell’s sensitivity value of complex in amyl acetate were 18,660 lit/mol cm and 6.0 × 10−3 μg/cm2, respectively. The composition of cadmium(II)–bis-(4-fluoroPM)TCH–pyridine adduct was established by slope ratio, mole ratio and Job’s method. Effects of foreign ions were also studied and use of suitable masking agent enhances the selectivity of method. Method has been successfully applied for determination of cadmium(II) in binary and synthetic mixtures, thin films, pharmaceuticals, coatings of ships, alloys, weeds in water and spiked water samples. The results obtained of proposed method were judged by using AAS for testing the validity of method. All the obtained results indicate a reliable, precise and fast analytical method for the extraction and quantification of trace levels of cadmium(II) from various synthetic and real samples without the use of sophisticated instrumentation and procedure.

Crystal structures of a series of bis-(acetyl-aceto-nato)oxovanadium(IV) complexes containing N-donor pyridyl ligands.

Crystal structures for a series of bis-(acetyl-acetonato)oxovanadium(IV) complexes containing N-donor pyridyl ligands are reported, namely, bis-(acetyl-acetonato-κ2 O,O')oxido(pyridine-κN)vanadium(IV), [V(C5H7O2)2O(C5H5N)], 1, bis-(acetyl-acetonato-κ2 O,O')oxido(pyridine-4-carbo-nitrile-κN)vanadium(IV), [V(C5H7O2)2O(C6H4N2)], 2, and bis-(acetyl-acetonato-κ2 O,O')(4-meth-oxy-pyridine-κN)oxidovanadium(IV), [V(C5H7O2)2O(C6H7NO)], 3, Compounds 1-3 have the formulae VO(C5H7O2)2 L, where L = pyridine (1), 4-cyano-pyridine (2), and 4-meth-oxy-pyridine (3). Compound 1 was previously reported [Meicheng et al. (1984 ▸). Kexue Tongbao, 29, 759-764 and DaSilva, Spiazzi, Bortolotto & Burrow (2007). Acta Crystallogr., E63, m2422] and redetermined here at cryogenic temperatures. Compounds 1 and 2 as pyridine and 4-cyano-pyridine adducts, respectively, crystallize as distorted octa-hedral structures with the oxo and pyridyl ligands trans to one another. A crystallographic twofold axis runs through the O-V-N bonds. Compound 3 containing a 4-meth-oxy-pyridine ligand crystallizes as a distorted octa-hedral structure with the oxo and pyridyl ligands cis to one other, removing the twofold symmetry seen in the other complexes.

P⋯N type pnicogen bonding in phosphorus trichloride–pyridine adduct: A matrix isolation infrared, DFT and ab initio study

Matrix isolation infrared spectroscopy in low temperature N2 matrices with the support of Density Functional Theory (DFT) and ab initio computations have been employed to investigate noncovalent forces formed between phosporous trichloride (PCl3) and hetero cyclic Pyridine (C5H5N) molecules. The possible geometries of PCl3–C5H5N adducts were optimized by computations performed at B3LYP/6–311++G(d,p) and MP2/6–311++G(d,p) levels of theory. Two minima, a global minimum and a local minimum, on the potential energy surface have been obtained for PCl3–C5H5N adduct system and the main force of interaction for their stabilization is pnicogen bonding (phosphorus bonding). The global minimum is stabilized by Cl–P⋯N interaction whereas local minimum is stabilized by Cl–P···π interaction. Interestingly, experiments revealed large red shift of 48.5 cm−1 for P–Cl stretching vibrational mode (ν3) in N2 matrix and this magnitude of shift is in good agreement with computational shift for PCl3–C5H5N adduct which is stabilized by Cl–P⋯N interaction. Moreover, computations predicted that P⋯N interacting adduct is stronger than the P···π interacting adduct by 2.02 kcal/mol at MP2/6–311++G(d,p) levels of theory. To understand the nature of interactions and the effect of charge transfer interaction on the stability of the adducts, Atoms In Molecules (AIM) and Natural Bond Orbital (NBO) analysis were performed.

A trigold carbide cation stabilized as a labile pyridine adduct

Auration of trimethylsilyldiazomethane by an (N-heterocyclic carbene)gold alkoxide affords a stable (silyldiazoalkyl)gold complex. The reaction of this species with a gold(I) fluoride, more efficient in the presence of an added gold cation equivalent, results in auration, desilylation, and N2 loss. The putative trigold carbide cation was isolated as its pyridine adduct, a stable N-(triauromethyl)pyridinium ion. Reaction of the cationic pyridine adduct with carbon monoxide breaks the CN bond, forming the stable trigold ketenylidene cation. DFT studies suggest substantial negative charge at the bridging carbon in the methylpyridinium analogue and in two possible intermediates, the trigold carbide cation and the pyridine adduct of a neutral digold carbide.

Solution and Solid-State Characterization of PbSe Precursors.

The addition of lead to diphenyl diselenide in ethylenediamine (en) or pyridine (py) allowed for the observation of the solvento complexes, (en)Pb(SePh)2 or (py)2Pb(SePh)2, respectively. Performing this reaction in dimethyl sulfoxide and subsequent crystallization was found to afford Pb(SePh)2. Inductively coupled plasma optical emission spectroscopy revealed a 1:2 lead to selenium ratio for all three complexes. Nuclear magnetic resonance spectroscopy confirms that Pb(SePh)2 is readily solubilized by ethylenediamine, and electrospray ionization mass spectrometry supports the presence of Pb(SePh)2 moieties in solution. Single-crystal X-ray diffraction analysis of the pyridine adduct, (py)2Pb(SePh)2, revealed a seesaw molecular geometry featuring equatorial phenylselenolate ligands. Crystals of Pb(SePh)2 grown from dimethyl sulfoxide revealed one-dimensional polymeric chains of Pb(SePh)2. We believe that the lead(II) phenylselenolate complexes form via an oxidative addition reaction.

Phenylmethylene, an intermediate of perchloric acid catalyzed oxygen absorption by styrene oxide in a polar solvent

Under conventional conditions of styrene oxide conversion catalyzed by perchloric acid in an alcohol solution (ButOH-chlorobenzene (9 : 1 by vol.), 343 K), an iminium ylide absorption band (λmax ≈ 460–470 nm) was recorded in the presence of pyridine trap, which corresponds to the adduct of pyridine and phenylmethylene. In the presence of oxygen, another intermediate product was detected, the absorption band of which (λmax ≈ 400 nm) coincides with the corresponding carbonyl oxide absorption. A similar observation was made earlier for the acid-catalyzed conversion of styrene oxide in the presence of p-toluenesulfonic acid in alcohol and acetonitrile solutions. Thus, the obtained results confirm formation of active intermediate species of carbene nature in two epoxide-acid systems.

Analytical strategies for the identification and characterization of protein adducts with HNE and related compounds

Advanced Lipoxidation Endproduct (ALEs) are modified proteins that can act as pathogenic factors in several chronic diseases, like diabetes and cardiovascular diseases [1]. These covalent adducts belong to a heterogeneous class of compounds derived from the protein adduction by reactive carbonyl species (RCS), which are generated upon lipid peroxidation. A similar class of compounds, Advanced Glycation Endproducts (AGEs), exhibit the same damaging effects as ALEs, partly due to binding to the Receptor for Advanced Glycation End products (RAGE). Using this receptor as a stationary phase for affinity chromatography, modified proteins could be potentially entrapped and enriched from any sample, to identify and characterize the origin of the modification. Applying this innovative approach, it has been shown already that AGEs can be captured, enabling the full characterization of the adducted moieties and site of modification using a bottom-up approach [2]. In order to validate this strategy for ALEs, and with the aim to understand whether ALEs are also binder of RAGE, fully characterized ALEs were produced in-vitro, by incubating human serum albumin (HSA) with glyoxal (GO), methylglyoxal (MG), 4-hydroxynonenal (HNE), acrolein (ACR) and malondialdehyde (MDA). The formation of ALEs was confirmed using a top-down MS approach by direct infusion on a triple-quadrupole mass spectrometer and the modifications and sites of adduction fully characterized by a bottom-up approach. The in-vitro produced ALEs were then subjected to VC1 Pull-Down relying on magnetic beads bound to VC1, the domain of RAGE necessary for binding, which can easily be separated. ALEs will be retained by VC1 and unbound protein can be easily removed, enriching ALEs in the sample. After binding, ALEs are eluted from the magnetic beads and subjected to GeLC-MS/MS to identify and localize the modification. Data obtained using this method were analysed using a targeted approach based on setting known modifications. Results obtained using VC1 Pull-Down were compared to the results of the in-solution digested ALEs and showed that ALEs containing a cyclic moiety induced by the modifications, are better retained by VC1, including pyrimidine, pyridine, pyraline and imidazolone adducts. Another observation is the binding of ALEs containing a carboxy-derivative, since these adducts exhibit a negative charge and increases the binding specificity to VC1, which has a positive charge. Semi-quantitative analysis also showed an enrichment of ALEs from VC1 Pull-Down, compared to unenriched sample. Results showed that VC1 can be used as a stationary phase to selectively enrich ALEs, depending on the structure and nature of the modification. Different applications of this technique are underway to identify and characterize ALEs and AGEs from samples of patients affected by diseases involving oxidative stress. In conclusion, we have found that besides AGEs, also ALEs are RAGE binders. ALEs involvement in the RAGE dependent proinflammatory cascade is currently under investigation.

A Review of Organotin Compounds: Chemistry and Applications

The field of organotin chemistry has a long history that started since 1849, when Frankland isolated a specimen of diethyltin diiodide [1]. In 1852, Lowich reported on the reaction of alkyl halides with a tin-sodium alloy giving alkyltin compounds [2]. This last publication is usually considered to represent the beginning of organotin chemistry. By 1935, about hundreds of publications concerning organotin chemistry had appeared in the literature. At that time, important names had played a role in the development of organotin chemistry were Krause in Germany, Kraus in the United States, and Kozeshkov in Russia. The discovery of organotin compounds industrial applications as polyvinyl chloride (PVC) stabilizers, as agrochemicals, biocides, and wood preservatives produced a revival of organotin chemistry. Particularly van der Kerk and his co-workers in Netherlands played a major role in this development [3,4]. In early of 1960s it was found that the tin atom in organ tin compounds is capable of extending its coordination number beyond four. Based on colligative studies, the trimethyltin chloride pyridine adduct, Figure 1, was the first documented fivecoordinate triorganotin halide complex that was proven by X-ray crystal structure [5]. Though divalent tin compounds had known for a long time, bis (cyclopentadienyl) tin (II) was the first example of a divalent organotin compound that was reported in 1956 [6].

Direct Access to Titanocene Imides via Bis(η5:η1-penta-fulvene)titanium Complexes and Primary Amines

The formation of the titanocene imido complexes 2b, 4, and 5 via double N–H bond activations at ambient temperature of sterically demanding amines (2,6-diisopropylaniline, tert-butylamine) by the use of the bis(η5:η1-adamantylidenepentafulvene)titanium complex (1) has been investigated. The titanium imido complex 2b exists in equilibrium with its corresponding titanium monoamide complex 2a. The equilibrium can be shifted to the side of the imide 2b by increasing the temperature. Starting from the equilibrium 2a/2b, or the titanium imido pyridine adduct 5, a broad range of [2 + 2] cycloaddition reactions are realized. In reactions with alkynes, the regioselective formation of the azacyclobutenes 6 and 7 are observed. By using carbodiimides, asymmetric (8 and 10a) and symmetric cycloaddition products (9 and 10b) are formed. In the reaction with isocyanates, dependent on the substitution pattern of the Ti═NR imido unit, the C═O or the C═N [2 + 2] cycloaddition occurs, resulting in the N,O-bound ureato(2-) co...

Metal-Free Acetylene Coupling by the (C6 F5 )2 B-X 1,2-Halogenoboration Reaction.

(C6 F5 )2 B-halides were conveniently prepared by treatment of (C6 F5 )2 BH with tritylchloride or -bromide, respectively. With cyclopropylacetylene, (C6 F5 )2 BBr underwent sequential cis-1,2-halogenoboration followed by 1,2-carboboration to give the 4-bromo-2,4-dicyclopropylbutadienyl-B(C6 F5 )2 product. It reacted further with additional cyclopropylacetylene to give the linear triene and tetraene products in a metal-free alkyne oligomerization reaction. The pyridine adduct of the initial diene product was characterized by X-ray diffraction. (C6 F5 )2 BCl reacted analogously. Similar (C6 F5 )2 BX induced oligomerization reactions were carried out with two conjugated enynes.

A Neutral RuII Hydride Complex for the Regio- and Chemoselective Reduction of N-Silylpyridinium Ions.

A detailed experimental analysis of the 1,4-selective reduction of pyridine with hydrosilanes catalyzed by a coordinatively unsaturated RuII thiolate complex is reported. The previously suggested intermediates, N-silylpyridinium ions and a neutral RuII hydride, have been independently synthesized and do indeed participate in the catalytic cycle. The resting state is not the cationic RuII complex initially used as the catalyst but its pyridine-coordinated congener. All RuII complexes, including the one resulting from hydrosilane activation, are in equilibrium with each other. The N-silylated 1,4-dihydropyridine together with the cationic RuII complex convert back into the corresponding N-silylpyridinium ion and the neutral RuII hydride (retro-hydrosilylation), followed by further backward reaction into the hydrosilane and the pyridine adduct of the cationic complex. These steps prove the overall reversibility of the transformation.

Pyridine 1:1 adducts of urea (Z' = 1) and thiourea (Z' = 8).

During our studies of urea and thiourea adducts, we noticed that no adducts with unsubstituted pyridine had been structurally investigated. The 1:1 adduct of pyridine and urea, C5H5N·CH4N2O, crystallizes in the P21/c space group with Z= 4. The structure is of a standard type for urea adducts, whereby the urea molecules form a ribbon, parallel to the a axis, consisting of linked R22(8) rings, and the pyridine molecules are attached to the periphery of the ribbon by bifurcated (N-H...)2N hydrogen bonds. The 1:1 adduct of pyridine and thiourea, C5H5N·CH4N2S, crystallizes in the P21/n space group, with Z = 32 (Z' = 8). The structure displays similar ribbons to those of the urea adduct. There are two independent ribbons parallel to the b axis at z ≃ 0 and 1/2, and three at z ≃ 1/4 and 3/4; the latter are crosslinked to form a layer structure by additional long N-H...S interactions, which each formally replace one branch of a bifurcated hydrogen-bond system.

Synthetic methodology: Labelling of bioactive azaarenes

Phosphonium adducts of pyridines are labile in basic solution, an undesirable property with regard to organic synthesis. Yet, this very lability proves valuable for the labelling of pyridine and diazines with heavier isotopes of hydrogen.

Dynamic Interconversion between Boroxine Cages Based on Pyridine Ligation.

Dynamic interconversion between large covalent organic cages was achieved simply by heating or acid/base treatment. A mixture of the boroxine cages 12-mer and 15-mer was cleanly converted into a pyridine adduct of the 9-mer boroxine cage upon treatment with pyridine, and the geometry of N-coordinated boron atoms changed from trigonal to tetrahedral. The reverse reaction was achieved by heating or acid treatment. In this process, the larger boroxine cages 12-mer and 15-mer were found to be entropically favored owing to the release of free pyridine molecules from 9-mer⋅6 Py.

Dynamic Interconversion between Boroxine Cages Based on Pyridine Ligation

AbstractDynamic interconversion between large covalent organic cages was achieved simply by heating or acid/base treatment. A mixture of the boroxine cages 12‐mer and 15‐mer was cleanly converted into a pyridine adduct of the 9‐mer boroxine cage upon treatment with pyridine, and the geometry of N‐coordinated boron atoms changed from trigonal to tetrahedral. The reverse reaction was achieved by heating or acid treatment. In this process, the larger boroxine cages 12‐mer and 15‐mer were found to be entropically favored owing to the release of free pyridine molecules from 9‐mer⋅6 Py.