Pyridazine Ligands Research Articles

Rigid molecular racks featuring the 1,10-phenanthroline ligand especially those co-functionalised with redox-active groups or other bidentate ligands

Abstract 6,7-Diazaphencyclone (DAPC), prepared for the first time, exists as a dimer in the solid state but is in thermal equilibrium with the monomer 11 in solution. DAPC is a reactive diene reacting with ring-strained and electron-deficient dienophiles with high stereospecificity. Bridged 1,10-phenanthrolines with different separation distances and ligand, ligand orientations have been prepared and mixed ligand systems are described with diazafluorene and 3,6-di(2-pyridyl)pyridazine ligand components. New diad and triad systems are reported which contain redox-active components linked to ligand centres. The rigid nature of the polyalicyclic molrac framework and the fusion method used to attach the functionality, provides molecules with exact geometric positioning and orientation of chromophores. This makes these systems key molecules for the study of electron-transfer and energy-transfer processes.

1,2-Metallotropic shifts in tricarbonylrhenium(I) complexes of pyridazine (pydz): a dynamic NMR investigation of the effects of cis-chelating ligands

Complexes of general formula fac-[Re(CO) 3(L–L)(pydz)][BF 4] (L–L=neutral bidentate chelate ligand; pydz=pyridazine) were prepared in high yield from fac-[ReBr(CO) 3(L–L)]. The pyridazine ligand coordinates to the metal moiety in a monodentate fashion, and undergoes a facile intramolecular 1,2-Re–N shift. The kinetics of the 1,2-metallotropic shift were measured by either one-dimensional NMR bandshape analysis or two-dimensional exchange spectroscopy. The free energies of activation, Δ G ≠ (298 K), were found to be dependent on the nature of the chelate ligand, and were in the range 77–87 kJ mol −1. The origins of the chelate ligand effects are discussed.

The synthesis of inward-facing 3,6-di(2-pyridyl)pyridazine ligands

A new class of inward-facing bis(dpp-ligands) fused to rigid molecular racks are reported, eg 17 and 19. The 3,6-di(2-pyridyl)pyridazine ligand units are formed by the reaction of 3,6-di(2-pyridyl) s-tetrazine with molrac bis(olefins), eg 11 and 18 (followed by oxidation of the intermediate dihydropyridazines); additionally mono-olefin, mono-pyridazines 14 and 21 are reported. Molecular modelling and comments of the mechanism of product formation are included.

The preparation of space-separated chelating agents based on the 3,6-dipyridyl pyridazine ligand

Linear, bent, cavity and Z-shaped molracs of varying length are converted to end-functionalised bis-chelating agents 3 containing the 3,6-(di-2′-pyridyl)pyridazine ligand by reaction of their norbornenyl end-groups with 3,6-di-(2′-pyridyl)- s-tetrazine 4 followed by oxidation with DDQ, sometimes in a one pot reaction. New representative molracs as well as new chelating agents are described. Molecular mechanics (MM2) has been used to evaluate geometric parameters for these systems which display ligand separations from 6–21 Å; however shorter or longer systems are possible.

Bicyclic [ b]-heteroannulated pyridazine derivatives—II. Structure-activity relationships in the 6-aryltriazolo-[4,3- b]pyridazine ligands of the benzodiazepine receptor

Electronic parameters (molecular electrostatic potential MEP, charge distribution on the nitrogen atoms, dipole moment μ and ionization potential IP) were calculated by semiempirical quantum chemistry methods for 2 sets (X = H and m-CF 3, the syn- and anti-rotamers of the latter being considered separately) of the 6-aryl-3-substituted-triazolo[4,3- b]pyridazine ligands of the benzodiazepine receptors (Figure 1; for X and Y c.f. Table 1). The calculations located the deepest MEP minimum near the =NN= fragment of the triazole ring (Figure 2). Activity of the investigated compounds (1 μM), expressed as % inhibition of in vitro 3H-diazepam (1.5 nM) binding, revealed a significant dependence on IP, which combined in correlation studies with the hydrophobic constants π X and π Y and the Swain-Lupton field constant X Y gave a 100 % explanation of variance (Equations 1–3). However, extrapolation pointed to a compound with excessive hydrophobicity. The dipole moment orientation, roughly consistent with the C(6)-aryl main molecular axis, was considered as another factor controlling the docking of the investigated triazolopyridazine ligands to the benzodiazepine receptor (Figure 3). A model of the triazolopyridazine-benzodiazepine receptor interaction was proposed (Figure 4).

Structural characterization of pyridazine (pydz) adducts of MX2(M = Mn, Fe, Co, Ni, Cu or Zn; X = Cl or Br). Ab-initio X-ray powder diffraction determination of polymeric [NiX2(pydz) complexes

The pyridazine (pydz) complexes of metal halides MX2(M = Mn, Fe, Co, Ni, Cu or Zn; X = Cl or Br) have been prepared, using a reagent molar ratio of 1 : 1, and investigated by X-ray powder diffraction methods. The crystal structures (orthorhombic, space group Imma, Z= 4) of [NiCl2(pydz)] and [NiBr2(pydz)]; have been determined, ab initio. from laboratory X-ray powder diffraction data only: [NiCl2(pydz)], a= 7.3758(4), b= 6.6069(3) and c= 1 2.7292(7)A, [NiBr2(pydz)], a= 7.5598(9), b= 6.8029(8) and c = 1 2.905(2) A. The structures have been solved by direct methods, and refined by the Rietveld technique down to Rprofilevalues of 0.062 and 0.078, respectively, for 4400 data points collected at room temperature in the range 17 < 2θ < 105°. Both compounds consist of infinite polymeric chains of nickel atoms, bridged by X (Cl or Br) and pyridazine ligands, showing an octahedral arrangement and trans-DH4h, NiX4N2 chromophores. The Ni–Cl and Ni–Br distances are 2.422(1) and 2.560(2)A, respectively. Analyses of the other species have shown that the analogues of Mn, Fe and Co are isomorphous with the nickel compounds, while those of Cu and Zn display different diffraction patterns.

Structure of (nitrato-O)(nitrato-O,O')tris(pyridazine-N)copper(II)

The coordination polyhedron about the copper(II) atom in Cu(pdz) 3 (NO 3 ) 2 , where pdz is pyridazine, is a distorted octahedron consisting of three N atoms from the pyridazine ligands, one O atom from the monodentate nitrate group and two O atoms from the unsymmetrically bidentate nitrate group

Copper(II) coordination chemistry of potentially octadentate (N 8) tetrapyridyl and tetrapyrazolyl-pyridazine ligands. X-ray crystal structures of [Cu 2(PTAPY)Br 4]·2DMF and [Cu 2(PTAPY)(NO 3) 2(N 3)(H 2O)] 2(NO 3) 2·1.2CH 3OH

The structural, electrochemical, ESR and magnetic properties of a series of dinuclear copper(II) complexes of two new polyfunctional pyridazine ligands, 3,6-bis( N,N,N′,N′-tetrakis(pyridine-2-ylmethyl)-aminoethanethiolato pyridazine (PTAPY), and 3,6-bis( N,N,N′,N′-tetrakis(pyrazol-1-ylmethyl)-aminoethanethiolato pyridazine (PTAPZ) are discussed. PTAPY and PTAPZ are potentially octadentate (N 8) ligands and on reaction with copper(II) salts form dinuclear complexes, [Cu 2(PTAPY)X 4]·yH 2O (X=NO 3, y=1 ( I); X=Br, y=2 ( II)), [Cu 2(PTAPY)(CH 3CN) 2](ClO 4) 4·0.5C 2H 5OH ( III), [Cu 2(PTAPZ)Cl 4]·5H 2O ( V), and a tetranuclear complex [Cu 2(PTAPY)(NO 3) 2(N 3)(H 2O)] 2(NO 3) 2·1.2CH 3OH ( IV). The single crystal X-ray structures of compounds II and IV have been determined, and in each case the ligand is hexadentate. II ([Cu 2(PTAPY)Br 4]·2DMF) crystallized in the triclinic system, space group P 1 , with a=14.037(3), b=14.941(4), c=11.782(6) Å, α=103.77(3), β=106.08(3), γ=84.59(2)°, V=2305(2) Å 3 and Z=2 ( R=0.036 and R w=0.032). Two different five-coordinate (CuN 3Br 2) geometries exist within the same molecule. IV crystallized in the triclinic system, space group P 1 , with a=14.876(5), b=16.172(4), c=10.068(2) Å, α=95.45(2), β=108.40(2), γ=64.74(2)° and Z=2 ( R=0.058 and R w=0.051). The two copper atoms are quite different with six- (axially elongated, distorted tetragonal) and five- (distorted square- pyramidal) coordinate arrangements, and dimerization through azido nitrogens results in the formation of a tetranuclear azide bridged molecule. The pyridazine nitrogens remain uncoordinated in all complexes and there is no magnetic interaction between the distant copper centers. Cyclic voltammograms are characterized by the presence of either one ‘two-electron’ or two ‘one-electron’ (overlapping) reversible or quasi-reversible redox processes, associated with the reduction of the dinuclear copper(II) species to dinuclear copper(I) species.

Self‐Assembly of a Cu4 Complex with Coplanar Copper(I) Ions: Synthesis, Structure, and Electrochemical Properties

π-Stacking interactions in the nearly parallel 3,6-bis(2-pyridyl)-pyridazine (dppn) ligands probably account for the distortion of the planar Cu4 unit in 1 from a square to a rhombus. Each Cu atom is surrounded in a tetrahedral fashion by two N atoms from pyridine and two N atoms from pyridazine units; the chelate rings themselves are planar. The distance between the pairs of dppn ligands is 3.47 Å.

Dicopper(II) complexes of novel polyfunctional pyridazines: crystal structure and magnetic properties of bis[µ-pyridazine-3,6-dicarbaldehyde dioximato(1–)-κN1,N′:N2,N″]-bis[aqua(perchlorato-κO)copper(II)

Two novel pyridazine ligands with 3,6-CRNOH (R = H, H2L1; Ph, H2L2) oxime side chains were synthesised. The related copper(II) dinuclear complexes [Cu2(HL1)2(ClO4)2(H2O)2]1 and [Cu2(HL2)2(ClO4)2(MeOH)n]2 were obtained subsequently. The crystal structure of 1 was determined: space group P21/n, a= 12.031(6), b= 9.517(4), c= 9.973(5)A, β= 100.16(4)° and Z= 2. The copper(II) ions of the binuclear unit are bridged by the two diazine fragments of the two essentially planar tetradentate ligands with the oxime nitrogen atoms completing the equatorial co-ordination. Two intra-complex hydrogen bridges link the terminal oximato moieties to give dinucleating macrocyclic complexes. In complexes 1 and 2 the copper(II) is in a classical 4 + 2 environment. The magnetic properties of those compounds revealed a spin-singlet ground state in each case. The singlet-triplet energy gaps were found to be –536(2) for 1 and –545(4) cm–1 for 2. The low-lying states of the complexes are discussed in relation to the nearly planar structure of the macrocyclic complexes.

Synthetic conductive materials IV. Novel binuclear copper(II) complex as a donor to TCNQ

The binuclear copper(II) complex of Cu 2(PPA)Cl 4 was synthesized by refluxing of the 3,6-bis(2′pyridyl)-pyridazine(PPA) ligand with CuCl 2 in acetone for 2 hours. The green crystal was reacted with various amount of LiTCNQ in H 2O and then reacted with TCNQ. Three different composition of Cu 2 (PPA) and TCNQ have been identified by elemental analysis and quantitative analysis of solution state electronic spectra. The structure was confirmed by infrared spectra and mass spectra which shown the TCNQ, TCNQ and Cu 2 (PPA) peaks obviously. The electron spin resonance spectra have g=2.0078 which can be investigated as a result of strong coupling between Cu(II) and TCNQ. By using the weighted-average calculation, we found the Cu(II) in ratio of 0.02. The magnetic susceptibility and ESCA spectra coincide with the ESR results. The electric conductivity are shown thermally activated in the range of 10 −4 ∼ 10 −5 Scm −1 of n-type semiconductors.

ChemInform Abstract: Pentamethylcyclopentadienylrhodium Complexes with the Pyridazine Ligand. Molecular Structure of ((Rh(C5Me5))2(μ‐Cl)2(μ‐pydz))(ClO4)2·H2O (pydz = pyridazine).

AbstractThe preparation of the new mononuclear complexes (III), (IV), and (VI) containing unidentate pyridazine ligands is carried out according to the scheme.

Copper co-ordination chemistry of some quadridentate pyridazine and phthalazine (N4) thioether ligands. Binuclear copper(II) complexes exhibiting two-electron reduction at positive potentials

Binuclear, hydroxo-bridged, copper(II) complexes of a series of quadridentate pyridazine and phthalazine thioether ligands involving nitrogen donor groups (derived from pyridine, imidazole, benzimidazole) exhibit room-temperature magnetic moments in the range 1.1–1.7 B.M., indicative of antiferromagnetically coupled binuclear copper(II) centres. Cyclic voltammetry and coulometry on most of these systems indicate reversible or quasi-reversible redox processes, involving two-electron transfer, at positive potentials (0.23–0.49 V vs. a saturated calomel electrode in CH3CN or dimethylformamide). Mononuclear copper(II) derivatives, involving bidentate ligands, also exhibit reduction at positive potentials. Catecholase activity involving 3,5-di-t-butylbenzene1,2-diol has been demonstrated for the hydroxo-bridged complex [Cu2(ptpd)(OH)Cl3]·EtOH [ptpd = 3,6-di(2′-pyridylthio)pyridazine], in which a Michaelis-Menten kinetic treatment gave KM= 3.4 × 10–4 mol dm–3 and a value of kp= 2.1 × 10–2 s–1 for the dissociation of the catechol–complex intermediate.

Binuclear antiferromagnetically-coupled hydroxo-bridged copper(II) complexes with positive reduction potentials and involving sequential two electron transfer at the same potential

Binuclear hydroxo-bridged copper(II) complexes of some tetradentate phthalazine and pyridazine ligands represent the first examples of binuclear copper(II) complexes exhibiting sequential two electron reduction at positive potentials (0.40 to 0.45 V vs. standard calomel electrode), comparable to those observed for Type III copper protein centres.