Electrochemical Synthesis and Characterisation of Alternating Tripyridyl–Dipyrrole Molecular Strands with Multiple Nitrogen‐Based Donor–Acceptor Binding Sites

Synthesis of alternating pyridine–pyrrole molecular strands composed of two electron‐rich pyrrole units (donors) sandwiched between three pyridinic cores (acceptors) is described. The envisioned strategy was a smooth electrosynthesis process involving ring contraction of corresponding tripyridyl–dipyridazine precursors. 2,6‐Bis[6‐(pyridazin‐3‐yl)]pyridine ligands 2 a – c bearing pyridine residues at the terminal positions were prepared in suitable quantities by a Negishi metal cross‐coupling procedure. The yields of heterocyclic coupling between 2‐pyridyl zinc bromide reagents 12 a – c and 2,6‐bis(6‐trifluoromethanesulfonylpyridazin‐3‐yl)pyridine increased from 68 to 95 % following introduction of electron‐donating methyl groups on the metallated halogenopyridine units. Favorable conditions for preparative electrochemical reduction of tripyridyl–dipyridazines 2 b , c were established in THF/acetate buffer (pH 4.6)/acetonitrile to give the targeted 2,6‐bis[5‐(pyridin‐2‐yl)pyrrol‐2‐yl]pyridines 1 b and 1 c in good yields. The absorption behavior of the donor–acceptor tripyridyl–dipyrrole ligands was evaluated and compared to theoretical calculations. Highly fluorescent properties of these chromophores were found (ν_em≈2×10⁴ cm^?1 in MeOH and CH₂Cl₂), and both pyrrolic ligands exhibit a remarkable quantum yield in CH₂Cl₂ (?_f=0.10). Structural studies in the solid state established the preferred cis conformation of the dipyrrolic ligands, which adopting a planar arrangement with an embedded molecule of water having a complexation energy exceeding 10 kcal mol^?1. The ability of the tripyridyl–dipyrrole to complex two copper(II) ions in a pentacoordinate square was investigated.     

trans‐(2‐Acetylpyridine‐κ2N,O)dichlorobis(dimethyl sulfoxide‐κS)ruthenium(II)

In the title complex, [RuCl₂(C₇H₇NO)(C₂H₆OS)₂], the metal ion is at the centre of a distorted octahedral NOCl₂S₂ coordination sphere. The neutral 2‐acetyl­pyridine ligand binds to the metal ion through the pyridine N and carbonyl O atoms, forming a five‐membered chelate ring. The monodentate S‐coordinating di­methyl sulfoxide mol­ecules are mutually cis, and the two remaining positions in the coordination sphere are occupied by two mutually trans Cl^? ions.     

Molecular tectonics: design,synthesis and structural analysis of thiacalixarene-based tectons

The synthesis of five new coordinating tectons based on tetrathiacalix[4]arene backbone was achieved and their structure analysed and confirmed by X-ray diffraction on single crystal. All tectons were based on tetrafunctionalisation of either tetrathiacalix[4]arene or tetramercaptotetrathiacalix[4]arene derivatives by four pyridine units. The junction between the pyridine units and the calix backbone was ensured by ester or thioester groups. On the pyridine ring, either position 3 or 4, defining the location of the coordination sites, were used to connect the monodentate site to the calix framework. To cite this article: H. Akdas et al., C. R. Chimie 6 (2003).     

Coordination polymers from kinetically labile copper(I) and silver(I) complexes: true macromolecules or solution aggregates?

Copper(I) and silver(I) coordination polymers have been prepared via conversion of equimolar amounts of o‐phenanthroline‐based bis‐bidentate ligand monomers, and [Cu(CH₃CN)₄]PF₆ or AgBF₄ as the respective metal comonomers. Using NMR spectroscopy, the homogeneous constitution of the diamagnetic products has been proved, and their average chain length has been estimated to be P_n ≥ 20. Moreover, NMR studies showed the multinuclear complexes to be open (dynamic) solution aggregates when dissolved in solvents that contain coordinating species like acetonitrile or pyridine. When strictly non‐coordinating solvents are used, on the other hand, the multinuclear complexes were found to be “true” polymers, i.e. macromolecules with a constant number of repeating units per individual chain in time. At very high dilution, finally, transformation of the originally formed chain molecules into cyclic oligomers was observed when coordinating solvents are used, but not in the case of non‐coordinating solvents.     

Synthese monodisperser linearer und cyclischer Oligomere der (R)-3-Hydroxybuttersäure mit bis zu 128 Einheiten

Monodisperse Linear and Cyclic Oligo[(R)-3-hydroxybutanoates] Containing up to 128 Monomeric Units Using benzyl ester/(tert-butyl)diphenylsilyl ether protection, (COCl)₂/pyridine esterification conditions, and a fragment-coupling strategy (with H₂/Pd-C debenzylation and HF · pyridine desilylation), linear oligomers of (R)-3-hydroxybutanoic acid (3-HB) containing up to 128 3-HB building blocks (mol. weight > 11 000 Da) are assembled (Schemes 1,2,5, and 6). In contrast to the previously employed protecting-group combination, and due to the low-temperature esterifying conditions, this procedure leads to monodisperse oligomers: all steps occur without loss of single 3-HB units. The product oligomers with two, one, and no terminal protecting groups (mostly prepared in multi-gram amounts) are characterized by all standard spectroscopic methods, especially by mass spectroscopy (Figs. 2 and 3), by their optical activity, and by elemental analyses. Cyclization of the oligo[(R)-3-hydroxybutanoic acids] with up to 32 3-HB units, using thiopyridine activation and CuBr₂ for the ring closure, produces oligolides consisting of up to 128 ring atoms (Scheme 7). Mixed oligolides containing 3-HB and (R)-3-hydroxypentanoic units are prepared from the corresponding linear trimers, using Yamaguchi's method for the ring closure (Scheme 8 and Fig.4 (X-ray crystal structures of two folded conformers)). Comparisons of melting points (Table 1), of [α] values (Tables 2 and 3), of ¹H-NMR coupling constants (Table 3), and of molecular volume/hydroxyalkanoate unit (Table 4) of linear and cyclic oligomer derivatives and of the high-molecular-weigh polymer show that the monodisperse oligomers appear to be surprisingly good models for the polymer. Besides this insight, our synthesis is supplying the samples to further test the role of P(3-HB) (ca. 140 units) as a component of complexes forming channels through cell-wall phospholipid bilayers.     

Methyl Iodide Accelerated Asymmetric Epoxidation of Alkenes Catalyzed by Chiral Salen-Mn（Ⅲ） Complexes with Tertiary Amine Units

A series of chiral salen-Mn（Ⅲ） complexes featuring two tertiary amine units were synthesized and employed in the enantioselective epoxidation of unfunctionalized alkenes in the presence of pyridine N-oxide and 2,6-dimethylpyridine N-oxide as proximal ligands, respectively. Moderate to high enantioselectivity and acceptable yields were achieved when NaClO was used as terminal oxidant under CH2Cl2/H2O biphasic media. Methyl iodide was found to be an effective additive to accelerate the epoxidation, possibly owing to the formation of quaternary ammonium units on catalysts, which may facilitate the reaction in an oil/water biphasic medium. The subsequent stimulation experiment was carried out, and the resulting ESI-HRMS analysis revealed the formation of a novel （salen）manganese（m） intermediate featuring two quaternary ammonium units, and bearing a pyridine N-oxide and a molecule of water simultaneously axially-coordinated backbone.     

Bis­[4‐(di­methyl­amino)­pyridinium] hexa­chloro­stannate(IV)

In the title compound, 4‐(di­methyl­amino)­pyridine is proton­ated on the pyridine N atom. The N(CH₃)₂ moiety is twisted 4.4 (2)° from the pyridine‐ring plane. The octahedral [SnCl₆]^2? anion is hydrogen bonded via trans‐Cl atoms to pyridinium N atoms from two cations forming (C₇H₁₁N₂)₂[SnCl₆] structural units.     

Di‐2‐pyridyl ketone p‐aminobenzoylhydrazone hydrate

The title compound [systematic name: 4‐amino‐2′‐(di‐2‐pyridyl­methyl­ene)­benzohydrazide hydrate], C₁₈H₁₅N₅O·H₂O, crystallizes in the triclinic space group P. Structural analysis shows one pyridine ring and the p‐amino­benzoylhydrazone moiety to be coplanar and orthogonal to the second pyridine ring. The packing reveals infinite molecular units interlocked via a network of hydrogen bonds.     

(4,4′‐Bipyridine)dichloroman­ganese(II), a two‐dimensional ­coordination polymer

The title compound, [MnCl₂(C₁₀H₈N₂)]_n, crystallizes with a two‐dimensional network constructed from linear chains of edge‐sharing MnCl₄ square‐planar units cross‐linked by bidentate 4,4′‐bi­pyridine bridges. The Mn atom and the bipyridine moieties lie on sites with 222 crystallographic symmetry; the Cl atom lies on a twofold axis. The bi­pyridine mol­ecule is twisted about the central C—C bond by 33.5 (3)°.     

Synthesis and crystal structure of an M4L6 tetrahedral cage with outward‐facing pockets from a substituted pyrazolyl–pyridine ligand

The self‐assembly of metal–polydentate ligands to give supramolecular tetrahedral complexes is of considerable current interest. A new ligand, 4‐benzyl‐2‐[1‐(2‐{[3‐(4‐benzylpyridin‐2‐yl)‐1H‐pyrazol‐1‐yl]methyl}benzyl)‐1H‐pyrazol‐3‐yl]pyridine (L), with chelating pyrazolyl–pyridine units substituted on the 4‐position of the pyridyl ring with benzyl units, has been synthesized and fully characterized. The self‐assembly of L with cobalt(II) gave rise to a tetrahedral cage (hexakis{μ‐4‐benzyl‐2‐[1‐(2‐{[3‐(4‐benzylpyridin‐2‐yl)‐1H‐pyrazol‐1‐yl]methyl}benzyl)‐1H‐pyrazol‐3‐yl]pyridine}perchloratotetracobalt(II) octakis(perchlorate) acetonitrile undecasolvate, [Co₄(ClO₄)(C₃₈H₃₂N₆)₆](ClO₄)₇·11CH₃CN) with approximate T symmetry. The X‐ray crystal structure of the cage, i.e. [Co₄L₆ClO₄](ClO₄)₇, shows that the substituted benzyl groups are oriented away from the centres of their respective ligands towards the Co^II vertices, making small outward‐facing pockets from three benzyl rings at the corners of the tetrahedron.     

Synthesis of nonactin (author's transl)]

Synthesis of Nonactin. The macrotetrolide antibiotic nonactin (I), containing four units of a C₁₀ hydroxy acid, has been synthesized starting from two adequately protected derivatives (III and IV) of nonactic acid (II). The 32-membered ring of the macrotetrolide is built up by a sequence of condensation and deprotection steps leading first to a product with two, and subsequently to one with four nonactic acid residues (VIII) which is then cyclized in the presence of Ag⁺-ions. Two reactions forming ester bonds have been developed to condense the hydroxy acids and to effect the final cyclization. In one the activation of the carboxyl group is achieved by conversion into the mixed anhydride with 2,4,6-trimethylbenzene sulfonyl chloride in pyridine. In the other the Ag⁺-ion induced reaction of a S-(2-pyridyl) hydroxy carbothioate is used to form the corresponding macrocyclic lactone. In the case of nonactin the ring closure is promoted by the coordinating effect of Ag⁺-ions present in the reaction mixture.     

Study of the Bonding Modes of Di‐2‐pyridyl ketoxime Ligand towards Ruthenium,Rhodium and Iridium Half Sandwich Complexes

The bonding modes of the ligand di‐2‐pyridyl ketoxime towards half‐sandwich arene ruthenium, Cp*Rh and Cp*Ir complexes were investigated. Di‐2‐pyridyl ketoxime {pyC(py)NOH} react with metal precursor [Cp*IrCl₂]₂ to give cationic oxime complexes of the general formula [Cp*Ir{pyC(py)NOH}Cl]PF₆ ( 1a ) and [Cp*Ir{pyC(py)NOH}Cl]PF₆ ( 1b ), for which two coordination isomers were observed by NMR spectroscopy. The molecular structures of the complexes revealed that in the major isomer the oxime nitrogen and one of the pyridine nitrogen atoms are coordinated to the central iridium atom forming a five membered metallocycle, whereas in the minor isomer both the pyridine nitrogen atoms are coordinated to the iridium atom forming a six membered metallacyclic ring. Di‐2‐pyridyl ketoxime react with [(arene)MCl₂]₂ to form complexes bearing formula [(p‐cymene)Ru{pyC(py)NOH}Cl]PF₆ ( 2 ); [(benzene)Ru{pyC(py)NOH}Cl]PF₆ ( 3 ), and [Cp*Rh{pyC(py)NOH}Cl]PF₆ ( 4 ). In case of complex 3 the ligand coordinates to the metal by using oxime nitrogen and one of the pyridine nitrogen atoms, whereas in complex 4 both the pyridine nitrogen atoms are coordinated to the metal ion. The complexes were fully characterized by spectroscopic techniques.     

Ring-Opened Hemiporphyrazines: Helical Molecules Exhibiting Circularly Polarized Luminescence

We designed and synthesized a new type of small helical molecule exhibiting intense circularly polarized luminescence (CPL) ( 1_2H ) by modifying a 20π-electron hemiporphyrazine with a large transition magnetic dipole moment. The hemiporphyrazine ring was opened and one additional pyridine unit was introduced, resulting in an overlap of two pyridine rings. X-ray structure analysis confirmed that 1_2H and its zinc complex ( 1_Zn ) adopt a helical geometry. A racemic mixture of 1_Zn was resolved into two enantiomers ((P)- and (M)- 1_Zn ), which exhibited CPL with a high luminescence dissymmetry factor (g_lum) value of ±2.1×10⁻². The origin of the large g_lum value was rationalized by means of DFT calculations. Helical structures could be formed in a diastereoselective manner by covalently attaching chiral units to the skeleton ( 1’_2H and 1’_Zn ). 1_Zn was found to possess chiral recognition ability for amines.     

Exo conformers of N‐(pyridin‐2‐yl)‐ and N‐(pyridin‐3‐yl)norbornene‐5,6‐dicarboximide crystals

Two isomeric pyridine‐substituted norbornenedicarboximide derivatives, namely N‐(pyridin‐2‐yl)‐exo‐norbornene‐5,6‐dicarboximide, (I), and N‐(pyridin‐3‐yl)‐exo‐norbornene‐5,6‐dicarboximide, (II), both C₁₄H₁₂N₂O₄, have been crystallized and their structures unequivocally determined by single‐crystal X‐ray diffraction. The molecules consist of norbornene moieties fused to a dicarboximide ring substituted at the N atom by either pyridin‐2‐yl or pyridin‐3‐yl in an anti configuration with respect to the double bond, thus affording exo isomers. In both compounds, the asymmetric unit consists of two independent molecules (Z′ = 2). In compound (I), the pyridine rings of the two independent molecules adopt different conformations, i.e. syn and anti, with respect to the methylene bridge. The intermolecular contacts of (I) are dominated by C—H...O interactions. In contrast, in compound (II), the pyridine rings of both molecules have an anti conformation and the two independent molecules are linked by carbonyl–carbonyl interactions, as well as by C—H...O and C—H...N contacts.     

The crystal structure of racemic and meso-diastereoisomers of aqua[2,6-bis(3-carboxy-1,2-dimethyl-2-azapropyl)pyridine]-Co(III) · Hexafluorophosphate · Di- and monohydrate,respectively

Synthesis of the pentadentate ligand 2,6-bis(3-carboxy-1,2-dimethyl-2-azapropyl)pyridine yields a mixture of the racemic and meso-isomers which it was difficult to separate by column chromatography. When the cationic Co(III)-complex of this ligand was crystallized with hexafluorophosphate as anion, two distinct crystalline forms were produced. The complex of the racemic ligand, 1 , has C₂ symmetry and is a dihydrate; a = 8.999(8), b = 12.047(6), c = 20.65(1) Å, orthorhombic, space group Peen,Z = 4, R = 0.074 for 1439 observed reflections. The complex of the meso-ligand, 2 , shows two independent molecules ( 2A and 2B ) per asymmetric unit, both monohydrates with a resolved disordered H₂O molecule in 2A ; a = 10.109(4), b = 12.835(2), c = 16.651(3) Å, α = 89.5(1)°, β = 84.7(3)°, γ = 88.6(3)°, triclinic, space group P1 , Z = 4, Rs = 0.054 for 4198 observed reflections. The coordination around the Co-atom is distorted octahedral in both complexes, with the coordinated H₂O molecule trans to the pyridine N-atom. In the racemic form of the complex, 1 , the pyridine ring is twisted about the Co-N(1) bond with respect to the plane defined by atoms Co, N(1), O(W1), N(2) and N(2P) by 17.2(2)°. In the meso-form of the complex, 2 , the CH₃ substituent C(8P) on atom C(4P), is now axial with respect to the 5-membered chelate ring. As a result of steric hinderance between atom O(1) and CH₃(8P), the pyridine ring has been displaced from the best mean-plane formed by atoms Co, O(W1), N(2) and N(2P). The principal axis of the pyridine ring C(3)…N(1), makes an angle of 14.1(1)° (mean) with this plane. At the same time the pyridine ring is twisted about axis C(3)…N(1) with respect to this plane by 19.7(1)° (mean).     

A grid‐like two‐dimensional AgI coordination polymer: poly[[[μ3‐N′‐(4‐cyanobenzylidene)isonicotinohydrazide]silver(I)] perchlorate]

This study presents new coordinating modes of a Schiff base with three coordinating groups and an interesting two‐dimensional framework based on two types of constructing units. In the title compound, {[Ag(C₁₄H₁₀N₄O)]ClO₄}_n, the Ag^I ion is coordinated by three N atoms and one O atom from three different N′‐(4‐cyanobenzylidene)isonicotinohydrazide (L) ligands, forming a primary distorted square‐planar coordination geometry. Two ligands each bridge two metal centres through one carbonitrile N atom in a monodentate mode and the hydrazide N and O atoms in a bidentate mode to form a small centrosymmetric (2+2)‐Ag₂L₂ ring as a principal constructing unit. The pyridyl N atoms from four ligands in four of these small rings coordinate to Ag atoms in adjacent rings to form a large hexanuclear silver grid. A two‐dimensional framework of rectangular grids is constructed from these small rings and large grids. Two perchlorate anions are located in each large grid and are bound to the grid by N—H...O hydrogen bonding. Crosslinking between the layers is achieved through long Ag...O interactions between the perchlorate anions and Ag atoms in adjacent layers.     

Five (1H‐pyrrol‐2‐yl)­pyridines

The title (1H‐pyrrol‐2‐yl)­pyridines, C₉H₈N₂, substituted at the ortho, meta, and para positions of the pyridine ring all have hydrogen‐bonded arrangements with geometrically similar, nearly linear, N(pyrrole)—H⋯N(pyridine) hydrogen bonds of average length. The graph sets for the ortho, meta, and three para polymorphs are R(10), C(6), C(7), C(7), and R(28), respectively.     

Syntheses,crystal structures and luminescence of 2,6- bis - (5-phenyl-1H-pyrazol-3-yl)pyridine and its d10 metal complexes

A new bis-pyrazole derivative, 2,6-bis-(5-phenyl-1H-pyrazol-3-yl) pyridine (H₂BPPP), and two d¹⁰ metal complexes [Zn(H₂BPPP)Cl₂](DMF)₂ (1), [Cd(H₂BPPP)Cl₂](DMF)₂ (2) have been synthesized and characterized. There is a tautomeric equilibrium of the bis-pyrazole compound in solution and the H atom of pyrazolyl NH can transfer to the adjacent N atoms. X-ray structure analyses reveal the H atom is on the 2-position of pyrazolyl ring in donor solvents, while the H atom is on the 1-position of pyrazolyl ring in metal complexes. The luminescence of the ligand and complexes have been investigated.     

First‐row transition metal–pyridine (py)–sulfate [(py)xM](SO4) complexes (M = Ni,Cu and Zn): crystal field theory in action

The crystal structures of three first‐row transition metal–pyridine–sulfate complexes, namely catena‐poly[[tetrakis(pyridine‐κN)nickel(II)]‐μ‐sulfato‐κ²O:O′], [Ni(SO₄)(C₅H₅N)₄]_n, (1), di‐μ‐sulfato‐κ⁴O:O‐bis[tris(pyridine‐κN)copper(II)], [Cu₂(SO₄)₂(C₅H₅N)₆], (2), and catena‐poly[[tetrakis(pyridine‐κN)zinc(II)]‐μ‐sulfato‐κ²O:O′‐[bis(pyridine‐κN)zinc(II)]‐μ‐sulfato‐κ²O:O′], [Zn₂(SO₄)₂(C₅H₅N)₆]_n, (3), are reported. Ni compound (1) displays a polymeric crystal structure, with infinite chains of Ni^II atoms adopting an octahedral N₄O₂ coordination environment that involves four pyridine ligands and two bridging sulfate ligands. Cu compound (2) features a dimeric molecular structure, with the Cu^II atoms possessing square‐pyramidal N₃O₂ coordination environments that contain three pyridine ligands and two bridging sulfate ligands. Zn compound (3) exhibits a polymeric crystal structure of infinite chains, with two alternating zinc coordination environments, i.e. octahedral N₄O₂ coordination involving four pyridine ligands and two bridging sulfate ligands, and tetrahedral N₂O₂ coordination containing two pyridine ligands and two bridging sulfate ligands. The observed coordination environments are consistent with those predicted by crystal field theory.     

Design, synthesis, and structural aspects of chalcogen-substituted pyridine dicarboxamide donors and their reactions

The design and synthesis of a new family of potentially pentadentate N₃Se₂ or N₃Te₂ type donors bearing a 2,6-disubstituted pyridine dicarboxamide moiety as the central fragment [-NH-C(O)-pyridine-C(O)-NH-] functionalized with chalcogen as additional donors in the appended arms of the pyridine ring through the alkyl spacers and their potential applications and reactivity toward d⁸ and d¹⁰ metal ions have been demonstrated.