Pyridine Subunits Research Articles

N-Phenylated Pyridine-Containing N2S2 Macrocycle

Single crystals of the N-phenylated 12-membered N2S2 macrocycle with a pyridine subunit were prepared and the crystal structure was analyzed. The title compound exhibits a chair-like conformation and the macrocyclic ring is folded over a pyridine subunit. Two S donors are exo-oriented to the macrocyclic ring cavity.

A hybrid macrocycle containing benzene and pyridine subunits is a better anion receptor than both its homoaromatic congeners

The hybrid tetraamide receptor 3 containing both 2,5-diamidopyridine and 1,3-diamidobenzene anion binding units has been synthesized. NOESY spectroscopy revealed that the new receptor is well preorganized for anion complexation, presumably owing to the macrocyclic topology and the rigidity of the 2,5-diamidopyridine unit. Association constants of 3 with several anions are higher than those determined earlier for its homoaromatic congeners 1 and 2 . X-ray crystallographic analysis of the chloride complex of hybrid macrocycle 3 enabled direct comparison of structural aspects of anion recognition by the 2,5-diamidopyridine and 1,3-diamidobenzene moieties.

Metal complexes of a new ligand derived from 2,3-quinoxalinedithiol and 2,6-bis(bromomethyl)pyridine

The synthesis of a new ligand containing quinoxaline and pyridine subunits is described. The reaction of 2,3-quinoxalinedithiol with 2,6-bis(bromomethyl)pyridine leads to the isolation of bis(2-thio-3-mercaptoquinoxalino)-2,6-dimethylpyridine (L), which is a macrocyclic ligand precursor. The reaction of transition metal ions with L gives [M(L)X]X complexes (where M = Mn(II), Co(II), Cu(II), Ag(I), Zn(II), or Cd(II), and X = Cl or Br). The compounds were characterized by physical and spectroscopic measurements which indicated that the ligand is probably acting as a pentadentate NS4 chelating agent

Metallosupramolecular zippers generated by self-organization of self-complementary molecular clefts.

The binding of Co(2+) and Pb(2+) ions to the terpyridine and pyridine subunits of the ligand 1 leads to the self-complementary molecular clefts 2-6, which result from the crossover combination of orthogonal-terpyridine and linear-pyridine metal-coordination subprograms and are stabilized by strong pi-pi stacking interactions. Four different cleft-type entities, [Co(2+) (2)(1)(2)] (3), [Pb(2+) (2)(1)(2)] (4), [Co(2+) (4)(1)(2)] (5), [Pb(2+) (4)(1)(2)] (6), are generated in both solution and the solid state, and may be interconverted as a function of metal/ligand stoichiometry. One- and two-dimensional metallosupramolecular zipper architectures result from self-assembly in the solid state driven by a combination of different pi-pi stacking subprograms. The U-shaped geometry of the ligand influences the possibility of zipping and thus, in turn, the generation of different zipper architectures. The structures of 2-5 have been confirmed by X-ray crystallography; that of 6 is based on NMR spectral data.

Polyhalogenated Heterocyclic Compounds. Macrocycles from Perfluoro‐4‐isopropylpyridine.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Self-assembly mechanism of a bimetallic europium triple-stranded helicate.

We report the self-assembly process of a supramolecular edifice based on the coordination of europium(III) by a ditopic strand L bearing tridentate bis(benzimidazolyl)pyridine subunits. Varying the metal/ligand ratio and using a fruitful combination of electrospray mass spectrometry and absorption spectrophotometry, we characterized three major complexes (EuL(2), Eu(2)L(2), and Eu(2)L(3)) in acetonitrile. Kinetic investigations showed an alternative "braiding" and "keystone" mechanism leading to Eu(2)L(3). The formation mechanism of the dinuclear triple-stranded helicate, which is mainly governed by electrostatic interactions, goes via the "side-by-side" Eu(2)L(2) intermediate. Our thermodynamic and kinetic data allow the prediction of the apparent "magic" self-assembly of Eu(2)L(3) which is fast and efficient only under a strict set of conditions.

Polyhalogenated heterocyclic compounds. Macrocycles from perfluoro-4-isopropylpyridine.

Perfluoro-4-isopropylpyridine was used as a building block for the two-step synthesis of a variety of macrocyclic systems bearing pyridine sub-units which were characterised by X-ray crystallography. Electrospray mass spectrometry revealed that complexation of either cations and, unusually, anions is possible depending on the structure of the macrocycle.

A periodic walk: a series of first-row transition metal complexes with the pentadentate ligand PY5.

A series of transition metal complexes derived from the pentadentate ligand PY5, 2,6-(bis-(bis-2-pyridyl)methoxymethane)pyridine, illustrates the intrinsic propensity of this ligand to complex metal ions. X-ray structural data are provided for six complexes (1-6) with cations of the general formula [M(II)(PY5)(Cl)](+), where M = Mn, Fe, Co, Ni, Cu, Zn. In complexes 1-4 and 6, the metal ions are coordinated in a distorted-octahedral fashion; the four terminal pyridines of PY5 occupy the equatorial sites while the axial positions are occupied by the bridging pyridine of PY5 and a chloride anion. Major distortions from an ideal octahedral geometry arise from displacement of the metal atom from the equatorial plane toward the chloride ligand and from differences in pyridine-metal-pyridine bond angles. The series of complexes shows that M(II) ions are consistently accommodated in the ligand by displacement of the metal ion from the PY5 pocket, a tilting of the axial pyridine subunit, and nonsymmetrical pyridine subunit ligation in the equatorial plane. The displacement from the ligand pocket increases with the ionic radius of M(II). The axial pyridine tilt, however, is approximately the same for all complexes and appears to be independent of the electronic ground state of M(II). In complex 5, the Cu(II) ion is coordinated by only four of the five pyridine subunits of the ligand, resulting in a square-pyramidal complex. The overall structural similarity of 5 with the other complexes reflects the strong tendency of PY5 to enforce a distorted-octahedral coordination geometry. Complexes 1-6 are further characterized in terms of solution magnetic susceptibility, electrochemical behavior, and optical properties. These show the high-spin nature of the complexes and the anticipated stabilization of the divalent oxidation state.

Missing-link macrocycles: hybrid heterocalixarene analogues formed from several different building blocks.

The synthesis and structural characterization of hybrid heterocalix[4]arene analogues containing pyrrole, benzene, methoxy-substituted benzene, and pyridine subunits is described. Macrocycles 1 and 2, examples of calix[2]benzene[2]pyrrole and calix[1]benzene[3]pyrrole systems, respectively, are synthesized by the condensation of pyrrole and an appropriate phenylbis(carbinol). Macrocycles 3 and 7, examples of calix[2]benzene[1]pyridine[1]pyrrole and calix[1]pyridine[3]pyrrole, respectively, are synthesized by the use of a carbene-based pyrrole-to-pyridine ring-expansion procedure. Single-crystal X-ray analysis reveals that compounds 1a, 1b, and 2b adopt 1,3-alternate conformations in the solid state, whereas compounds 3 and 7 display structures that are best described as "flattened partial cones" in terms of their conformation. (Series a refers to pure benzene-derived systems, whereas series b indicates macrocycles containing 5-methoxyphenyl subunits). In the solid state, the methoxy-functionalized macrocycles 1b and 2b, and the chloropyridine-containing macrocycle 7 exist as dimers. In the case of 1a and 7, these compounds interact with neutral solvent in the solid state. The conformations of the macrocycles in solution were explored by temperature-dependent proton NMR and NOESY spectral analysis. At 188 K, macrocycles 1a and 2a adopt flattened 1,3-alternate conformations, whereas macrocycles 3 and 7 exist in the form of flattened partial-cone conformations. Standard proton NMR titration analyses were carried out in the case of macrocycles 1a and 2a, and reveal that at least the second of these systems is capable of binding fluoride and chloride anions in CD(2)Cl(2) solution at room temperature (K(a)=571 and 17M(-1) in the case of 2a and F(-) and Cl(-), respectively).

Intermolecular CH⋯N/CH⋯O hydrogen bonds in the crystal structures of α,β-unsaturated ketones carrying a terminal pyridine subunit

α,β-Unsaturated ketones 1– 4 carrying a terminal pyridine subunit form aggregates in the crystalline state with the molecules linked together through CH⋯N/CH⋯O hydrogen bonds. The hydrogen-bonding motifs are discussed.

Programmed construction of discrete self-assembled cyclic aggregates

Examples for programmed self-assembly of alpha,beta-unsaturated ketoximes carrying a terminal pyridine subunit are described. The solid-state structures of a series of pyridinyl alpha,beta-unsaturated ketoximes 1 were investigated by X-ray structural analysis; this demonstrated that molecules 3-5 predictably form discrete cyclic aggregates stabilized by a network of hydrogen bonds and aromatic interactions.

Pyridine-based dendritic wedges with a specific metal ion coordination site and their palladium(II) complexes

The 2,6-di(thiomethyl)pyridine sub-unit has been incorporated into pyridine-based dendritic structures providing a series of dendritic wedges, which readily form PdII complexes.

Synthesis, coordination chemistry and crystal structures of [2+2] macrocycles incorporating 2,6-bis(thiomethyl)pyridine sub-units

A series of potentially dinucleating [2+2] macrocyclic ligands with two SNS metal-binding domains separated by a variable polymethylene chain have been prepared. Two examples of these ligands have been structurally characterised. These ligands form polymeric adducts with [Rh 2(O 2CCMe 3) 4] in which the ligands are thought to act as exocyclic S-donors to the axial sites of the dinuclear complex. In contrast, reaction with [(CO) 2Rh( μ-Cl) 2Rh(CO) 2] resulted in the formation of dinuclear complexes in which two Rh(CO) units are bound to each macrocyclic ligand.

Synthesis of Petrosins C and D

Petrosins C and D (5 and 6), diastereomers of the known natural products petrosin (1), petrosin A (2), and petrosin B (3), have been prepared. The synthetic route involved initial creation of a 16-membered bis-pyridine intermediate, exemplified by compounds 7, 28, and 52. Several different methods for formation of the macrocycle were evaluated, and the most efficient (Schemes 7−9) involved use of Z double bonds in the six-carbon chains linking the two pyridine rings. This approach permitted the two pyridine subunits (37 and 39) to be joined by alkylation of a lithiated α-methylpyridine with an allylic chloride (e.g., 37 + 39 → 40 and 49 → 45). Bisannulation of compounds 7 and 28 was complicated by a surprising lack of acidity of the α-pyridyl methylene groups. Eventually, this problem was solved by stepwise introduction of two allyl groups, using the more acidic sulfone for introduction of the first (e.g., 52 → 53) and direct allylation to introduce the second (e.g., 54 → 55 + 56). The bisannulation was c...

Ligand exchange and catalysis in phenylation reactions mediated by lead tetracarboxylates

An investigation of catalysis and ligand exchange in the arylation of nucleophiles with phenylboronic acid and mixed ligand lead(IV) complexes is described. Although this reaction is known to be catalyzed by mercury(II) acetate, other heavy metals have been shown to have a similar effect, albeit less efficiently. The effect of pyridine has been investigated with a range of chelating ligands containing a pyridine sub-unit.

Homocalixpyridines: Ligands Exhibiting High Selectivity in Extraction and Sensor Processes

A novel spherical host architecture, based on pyridine subunits, has been created. It exhibits selective complexing properties toward soft metal ions (right), which have been tested in extraction and sensor processes. The complex-forming behaviour can be tailored by variation of the size of the cavity and by substitution. Homocalixpyridines are interesting in view of their application as selective carriers in separation and sensing techniques.

‘Living’ Free-Radical Polymerization Process: A New Approach Towards Well-Defined Photochromic (CO) Polymers

Different copolymers of styrene and 4-vinylpyridine were prepared using an easy set-up ‘living’ free-radical polymerization method. After reaction with spiro[cyclopropene-1,9′-fluorenes] on to the pyridine subunits, photochromic coploymers are obtained with controlled weight. Compared to corresponding free dihydroindolizine, a slight bathochromic shift is observed.

ChemInform Abstract: Conjugated Macrocycles Related to the Porphyrins. Part 6. Oxypyriporphyrin, the First Fully Aromatic Porphyrinoid Macrocycle with a Pyridine Subunit.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and Luminescence of Novel EuIII Complexing Agents and Labels with 4‐(Phenylethynyl)pyridine Subunits

AbstractThe synthesis of novel 4‐(phenylethynyl)pyridine subunits containing H2O‐soluble complexing agents and their luminescence with EuIII ions are reported. Ligands with high luminescence intensities as well as quantum yields were obtained. Also the prepared labeling reagents as antibody conjugates gave the highest quantum and luminescence yields reported for H2O‐soluble EuIII labels.

Synthesis and Reductive Complexation Properties of a Cone‐Configurated Tetra[p‐(tert‐butyl)]calix[4]arene incorporating bipyridyl and pyridine subunits. NMR characterization and crystal structure of its chiral copper(I) complex

AbstractThe hetero‐armed p(tert‐butyl)calix[4]arene 1 was synthesized by a stepwise procedure. This ligand presented a very strong complexing behavior towards Cu1, giving the chiral complex 2 and parent species when reacted with CuII salts. High‐resolution NMR techniques were employed for the characterization of 2, demonstrating notably exchange processes between its two enantiomeric forms. The racemic nature of 2 was confirmed by X‐ray crystal‐structure analysis.