Monomeric, tetrameric, and polymeric copper di-tert-butyl phosphate complexes containing pyridine ancillary ligands

The reaction of di-tert-butyl phosphate (((t)BuO)(2)P(O)(OH), dtbp-H) with copper acetate in the presence of pyridine (py) and 2,4,6-trimethylpyridine (collidine) has been investigated. Copper acetate reacts with dtbp-H in a reaction medium containing pyridine, DMSO, THF, and CH(3)OH to yield a one-dimensional polymeric complex [Cu(dtbp)(2)(py)(2)(mu-OH(2))](n) (1) as blue hollow crystalline tubes. The copper atoms in 1 are octahedral and are surrounded by two terminal phosphate ligands, two pyridine molecules, and two bridging water molecules. The mu-OH(2) ligands that are present along the elongated Jahn-Teller axis are responsible for the formation of the one-dimensional polymeric structure. Recrystallization of 1 in a DMSO/THF/CH(3)OH mixture results in the reorganization of the polymer and its conversion to a more stable tetranuclear copper cluster [Cu(4)(mu(3)-OH)(2)(dtbp)(6)(py)(2)] (2) in about 60% yield. The molecular structure of 2 is made up of a tetranuclear core [Cu(4)(mu(3)-OH)(2)] which is surrounded by six bidentate bridging dtbp ligands. While two of the copper atoms are pentacoordinate with a tbp geometry, the other two copper atoms exhibit a pseudooctahedral geometry with five normal Cu-O bonds and an elongated Cu-O linkage. The pentacoordinate copper centers bear an axial pyridine ligand. The short Cu.Cu nonbonded distances in the tetranuclear core of 2 lead to magnetic ordering at low temperature with an antiferromagnetic coupling at approximately 20 K (J(P) = -44 cm(-1), J(c) = -66 cm(-1), g = 2.25, and rho = 0.8%). When the reaction between di-tert-butyl phosphate (dtbp-H) and copper acetate was carried out in the presence of collidine, large dark-blue crystals of monomeric copper complex [Cu(dtbp)(2)(collidine)(2)] (3) formed as the only product. A single-crystal X-ray diffraction study of 3 reveals a slightly distorted square-planar geometry around the copper atom. Thermogravimetric analysis of 1-3 revealed a facile decomposition of the coordinated ligands and dtbp to produce a copper phosphate material around 500 degrees C. An independent solid-state thermolysis of all the three complexes in bulk at 500-510 degrees C for 2 days produced copper pyrophosphate Cu(2)P(2)O(7) along with small quantities of Cu(PO(3))(2) as revealed by DR-UV spectroscopic and PXRD studies.     

Dioxygen-initiated oxidation of heteroatomic substrates incorporated into ancillary pyridine ligands of carboxylate-rich diiron(II) complexes

Progress toward the development of functional models of the carboxylate-bridged diiron active site in soluble methane monooxygenase is described in which potential substrates are introduced as substituents on bound pyridine ligands. Pyridine ligands incorporating a thiol, sulfide, sulfoxide, or phosphine moiety were allowed to react with the preassembled diiron(II) complex [Fe(2)(mu-O(2)CAr(R))(2)(O(2)CAr(R))(2)(THF)(2)], where (-)O(2)CAr(R) is a sterically hindered 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh). The resulting diiron(II) complexes were characterized crystallographically. Triply and doubly bridged compounds [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-MeSpy)] (4) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-MeS(O)py)(2)] (5) resulted when 2-methylthiopyridine (2-MeSpy) and 2-pyridylmethylsulfoxide (2-MeS(O)py), respectively, were employed. Another triply bridged diiron(II) complex, [Fe(2)(mu-O(2)CAr(4)(-)(FPh))(3)-(O(2)CAr(4)(-)(FPh))(2-Ph(2)Ppy)] (3), was obtained containing 2-diphenylphosphinopyridine (2-Ph(2)Ppy). The use of 2-mercaptopyridine (2-HSpy) produced the mononuclear complex [Fe(O(2)CAr(Tol))(2)(2-HSpy)(2)] (6a). Together with that of previously reported [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-PhSpy)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-Ph(2)Ppy)] (1), the dioxygen reactivity of these iron(II) complexes was investigated. A dioxygen-dependent intermediate (6b) formed upon exposure of 6a to O(2), the electronic structure of which was probed by various spectroscopic methods. Exposure of 4 and 5 to dioxygen revealed both sulfide and sulfoxide oxidation. Oxidation of 3 in CH(2)Cl(2) yields [Fe(2)(mu-OH)(2)(mu-O(2)CAr(4)(-)(FPh))(O(2)CAr(4)(-FPh))(3)(OH(2))(2-Ph(2)P(O)py)] (8), which contains the biologically relevant {Fe(2)(mu-OH)(2)(mu-O(2)CR)}(3+) core. This reaction is sensitive to the choice of carboxylate ligands, however, since the p-tolyl analogue 1 yielded a hexanuclear species, 7, upon oxidation.     

Synthesis and molecular structures of complexes of TlBrI2 with pyridine N-oxide and some substituted pyridine N-oxides

The following compounds, TlBrI₂(PyO)₂, TlBrI₂(2-PicO)₂, TlBrI₂(3-PicO)₂, TlBrI₂(4-PicO)₂, TlBrI₂(4-Cl-PyO)₂, TlBrI₂(4-CN-PyO)₂, TlBrI₂(4-NO₂-PyO)₂ and TlBrI₂(4-CH₃O-PyO)₂, have been prepared and characterized by elemental analysis. The solids behave as non-electrolytes in acetonitrile solution and are monomers in benzene. Vibrational (IR and Raman) spectra suggest that the most probable structure is that of a trigonal bipyramid with the halogen atoms in equatorial positions and the two ligands in axial positions.     

Infrared absorption spectra of pyridine N-oxide and benzoic acid complexes

The infrared absorption spectra in the 4000–1600cm⁻¹ region of some benzoic acid pyridine N-oxide derivative complexes are described.     

Catalysis by rhodium complexes bearing pyridine ligands: Mechanistic aspects

The present review describes several examples of the use of soluble and immobilized complexes of rhodium with pyridine ligands as catalysts. Examples include the water-gas shift reaction, the carbonylation of methanol, the reduction of nitroarenes, the hydrocarboxylation and oligomerization of CO/ethylene, the hydrocarbonylation of 1-hexene, the hydroesterification and hydroformylation–acetalization of 1-hexene, the hydrodechlorination of dichloroethane, the carbonylation of naphtha and the hydrogenation and hydroformylation of alkenes.     

Redox characteristics of manganese and cobalt complexes obtained from pyridine N-oxide

Manganese and cobalt complexes, using pyridine N-oxide as ligand, have been synthesized, and their cyclic and square-wave voltammetric measurements have been carried out. The results reveal that the complexes exhibit different voltammetric pattern, which suggests that the redox processes are most probably metal-centered. In both complexes, extra redox activity is observed once the potential exceeds certain value of the voltage. The observation of an oxidation wave in manganese complex at + 0.75 V vs. Ag/AgCl or + 0.95 V vs. NHE strongly suggests that this complex can bring about oxidation of water and can, thus, serve as a synthetic analogue of water oxidizing complex (WOC) of PS II.     

Flexible bidentate pyridine and chiral ligands in the self-assembly of supramolecular 3-D cages

Discrete, nanoscopic 3-D cages are prepared in high yield via coordination-driven self-assembly from a variety of building blocks, including bidentate 3-substituted pyridines, chiral, and silicon-based tripods. All are characterized by NMR ((31)P, (1)H) and electrospray ionization mass spectrometry.     

Introduction of new ancillary ligands to the iridium complexes having 2,3-diphenylquinolinato ligands for OLED

We investigated the effect of an ancillary ligand (AL) on the emission color and luminous efficiencies of its complex, Ir(4-Me-2,3-dpq)₂(AL), where 4-Me-2,3-dpq represents 4-methyl-2,3-diphenylquinolinato ligand. We expected that ancillary ligand modification by introduction of the bulky substituent to the complexes might allow luminous efficiency increase by reduction of T–T annihilation. Furthermore, some ancillary ligands may contribute to fine-tuning of their complex emission colors by influencing the energy level of Ir d-orbitals upon the orbital mixing. As new ancillary ligands substituting for acac which is a typical AL in the iridium complexes, pyrazolone-based ligands, 4-R-5-methyl-2-phenyl-2,4-dihydro-pyrazol-3-one series (przl-R), were prepared, where R represents C₆H₅, C₆H₄CH₃ and C₆H₄Cl. These ligands were chelated to the iridium center to yield a new series of the iridium complexes, Ir(4-Me-2,3-dpq)₂(przl-R). The X-ray crystal structure of Ir(4-Me-2,3-dpq)₂(przl-C₆H₄Cl) was determined. The electrochemical and luminescence properties of the iridium complexes were investigated. The effect of the przl-substituents on the emission colors of the complexes was not significant. On the other hand, the luminous efficiencies of Ir(4-Me-2,3-dpq)₂(przl-C₆H₅) and Ir(4-Me-2,3-dpq)₂(przl-C₆H₄CH₃) were higher than that of Ir(4-Me-2,3-dpq)₂(acac).     

Tuning photophysical properties with ancillary ligands in Ru(II) mono-diimine complexes

The series of complexes [XRu(CO)(L-L)(L′)₂][PF₆] (X = H, TFA, Cl; L-L = 2,2′-bipyridyl, 1,10-phenanthroline, 5-amino-1,10-phenanthroline and 4,4′-dicarboxylic-2,2′-bipyridyl; L′₂ = 2PPh₃, Ph₂PC₂H₄PPh_2, Ph₂PCHCHPPh₂) have been synthesized from the starting complex K[Ru(CO)₃(TFA)₃] (TFA = CF₃CO₂) by first reacting with the phosphine ligand, followed by reaction with the L-L and anion exchange with NaPF₆. In the case of L-L = phenanthroline and L′₂ = 2PPh₃, the neutral complex Ru(Ph₃P)(CO)(1,10-phenanthroline)(TFA)₂ is also obtained and its solid state structure is reported. Solid state structures are also reported for the cationic complexes where L-L = phenanthroline, L₂ = 2PPh₃ and X = Cl and for L-L = 2,2′-bipyridyl, L₂ = 2PPh₃ and X = H. All the complexes were characterized in solution by a combination of ¹H and ³¹P NMR, IR, mass spectrometry and elemental analyses. The purpose of the project was to synthesize a series of complexes that exhibit a range of excited-state lifetimes and that have large Stokes shifts, high quantum yields and high intrinsic polarizations associated with their metal-to-ligand charge-transfer (MLCT) emissions. To a large degree these goals have been realized in that excited-state lifetimes in the range of 100 ns to over 1 μs are observed. The lifetimes are sensitive to both solvent and the presence of oxygen. The measured quantum yields and intrinsic anisotropies are higher than for previously reported Ru(II) complexes. Interestingly, the neutral complex with one phosphine ligand shows no MLCT emission. Under the conditions of synthesis some of the initially formed complexes with X = TFA are converted to the corresponding hydrides or in the presence of chlorinated solvents to the corresponding chlorides, testifying to the lability of the TFA Ligand. The compounds show multiple reduction potentials which are chemically and electrochemically reversible in a few cases as examined by cyclic voltammetry. The relationships between the observed photophysical properties of the complexes and the nature of the ligands on the Ru(II) is discussed.     

Effects of electron-rich ancillary ligands on green and yellow-emitting bis-cyclometalated iridium complexes

Abstract

Six new green to yellow-emitting heteroleptic bis-cyclometalated iridium(III) complexes of the type Ir(C?N)₂(L?X) (C?N?=?cyclometalating ligand, L?X?=?monoanionic chelating ancillary ligand) bearing two widely used cyclometalating ligands (C?N?=?2-(2-thienyl)pyridine (thpy) and 2-phenylbenzoxazole (bo)) and six different ancillary ligands were prepared. In this study, the complexes include structurally diverse ancillary ligands that allow us to investigate several aspects of structure-property relationships. Ancillary ligands used in this study are small-bite-angle N-phenylacetamidate (paa), N-isopropylbenzamidate (ipba) and N,N′-diisopropylbenzamidinate (dipba), and larger bite-angle β-ketoiminate (acNac), β-diketiminate (NacNac), and β-thioketoiminate (SacNac). The emission color is governed by the choice of the cyclometalating ligand, but the ancillary ligands influence the electrochemical and photophysical properties. Electrochemical analysis shows that the energy of the HOMO varies substantially as the L?X structure is altered, whereas the energy of LUMO remains nearly constant. The emission maxima range from 537?nm to 590?nm, with solution quantum yields between 0.0094 and 0.60 and microsecond lifetimes. The results here reveal the ancillary ligands provide a channel to control redox properties and excited-state dynamics in cyclometalated iridium complexes that luminesce in the middle regions of the visible spectrum.     

Absorption spectra of some pyridine and pyridine N-oxide derivatives in oleum

The absorption spectra of a number of pyridlne and pyridine N-oxide derivatives in media of different acidity functions have been investigated. The bathochromic shift of the shortwave absorption band in oleum is interpreted as a consequence of the addition of a proton to the conjugate acid. The formation of a hydrogen bond between the 3-hydroxy derivative of the heterocyclic compounds investigated and the oleum, appearing as a hypsochromic shift of the long-wave absorption band, has been detected. This phenomenon is absent in the case of the 2-methoxy derivative.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 963–966, July, 1973.     

Metal ion complexes of 2-pyridylcarbinol N-oxide

Transition metal ion complexes of the potentially bidentate ligand 2-pyridylcarbinol N-oxide have been prepared. They are characterized and identified by chemical analysis and physical measurements. Their IR and electronic spectra are discussed with regard to monodentate or bidentate bonding of the ligand. The Cr(III) and Fe(III) complexes each contain two 2-pyridylcarbinol N-oxide ligands and a conjugate base of the carbinol in their coordination spheres. The remaining metal ions crystallized with either four (Mn(II), Ni(II), Cu(II), Zn(II)) or six (Co(II)) neutral ligands.     

Novel complexes of 2,6-(dibenzothiazol-2-yl)pyridine and related ligands

The coordination chemistry of 2,6-pyridinedicarboxaldehyde (Dial) has been recently reported¹. The Schiff base derived from Dial and o-aminobenzene     

Cation-radical of pyridine N-oxide and its reactions with C?H bonds

Visible absorption spectrum for the cation-radical of pyridine N-oxide pyO⁺ obtained in the oxidation of the appropriate N-oxide by the photo-excited triplet state of chloranil, has a wide maximum at =430–460 nm. pyO⁺ reacts with cyclohexane, methanol or toluene with the formation of intermediate complexes. Equilibrium constants of their formation K×10^–2 dm³/mol amount to 0.1, 1.0 and 2.0, respectively. The (pyO⁺...RH) complex readily reacts with O₂, and in the absence of O₂ its decomposition is independent of the hydrocarbon nature.

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- N- (pyO⁺) N- . pyO⁺ , =430–460 . , pyO⁺ , , , (×10^{–2 3}/) 0,1, 1,0 2,0. , .

     

Highly phosphorescent iridium complexes with chromophoric 2-(2-hydroxyphenyl)oxazole-based ancillary ligands: interligand energy-harvesting phosphorescence

We disclose a controlled phosphorescence color tuning in a series of cyclometalated heteroleptic IrIII complexes (IrIII bis(2-(2,4-difluorophenyl)pyridinato- C,N (2'))(LX)) containing chromophoric 2-(2-hydroxyphenyl)oxazole-derivative ancillary ligands (LX). From a cyclometalated chloride-bridged IrIII dimer, three highly emissive cyclometalated heteroleptic IrIII complexes were obtained in good yields, each with a different conjugative plane in the chromophoric ancillary ligand (i.e., 2-(2-hydroxyphenyl)-4-methyloxazole, 2-(2-hydroxyphenyl)-6-methylbenzoxazole, and 2-(2-hydroxyphenyl)naphthoxazole). The three IrIII complexes showed highly efficient greenish blue (500 nm), green (525 nm), and yellow (552 nm) phosphorescence, respectively; a regular ca. 0.11 eV bathochromic shift was observed for each additional phenyl ring fused to the oxazole ring in the ancillary ligand. From the absorption, electrochemical measurements, static and transient photoluminescence (PL), and time-dependent density functional theory (TD-DFT) calculations, it can be concluded that the IrIII complexes have a single emission center with dual excitation paths. Finally, this characteristic energy-harvesting phosphorescence was further demonstrated in electrophosphorescence devices.     

Cyclometalated Ir(III) complexes containing N-aryl picolinamide ancillary ligands

The reaction of the cyclometalated chloro-bridged iridium(III) dimer, [(ppy)₂ Ir(μ-Cl)]₂ (ppy - 2-phenyl pyridine) with N-aryl picolinamides (LH, LH-NO₂, LH-CH₃, LH-l, LH-F) resulted in the formation of neutral heteroleptic complexes [Ir(ppy)₂L] (1), [Ir(ppy)₂L-NO₂](2), [Ir(ppy)₂L-CH₃](3), [Ir(ppy)₂L-Cl](4) and [Ir(ppy)₂L-F] (5). These complexes contain a six-coordinate iridium with a 2C, 4N coordination environment. The N-aryl picolinamide ligands are deprotonated during complexation and the resulting amidates bind to iridium in a chelating manner (N, N). Optical spectroscopic studies revealed that the complexes 1-5 exhibited intense π→π^∗ absorptions in the ultraviolet region. In addition low energy transitions due to ¹MLCT, ¹LLCT and ³MLCT are also seen. The emission spectra of 1-5, upon excitation at 450 nm, show a single emission with a λ_max around 513 nm. The lifetimes of this emission are in between 7.4 and 9.6 μs while the quantum yields are quite high and range from 0.2 to 0.5. Based on density functional theory (DFT) calculations on 1 and 3, the three highest occupied orbitals are composed of ligand π orbitals mixed with Ir-d orbitals while the three lowest unoccupied orbitals are mostly π orbitals of the ligands. From the time dependent DFT calculations it is revealed that the lowest energy electronic singlet and triplet excitations are a mixture of MLCT and LLCT.     

IR spectroscopic studies on substituted pyridine N-oxide complexes of tin(IV) chloride in acetonitrile

Complexes of eleven substituted pyridine N-oxide donors with stannic chloride in acetonitrile solution were investigated ultizing IR spectroscopy. Two distinct types of behaviour were noted: (1) Pyridine N-oxide donors containing electron releasing substituents generally form strong complexes with SnCl₄ and exhibit maxima in continuous variation plots at a 2:1 ligand-to-metal ratio. Little or no free ligand is detected in these solutions until this ratio is exceeded. Ligands exhibiting this behaviour include the 2-methyl-, 3-methyl-, 4-methyl-, 4-methoxy- and 4-phenylpyridine N-oxides.(2) Pyridine N-oxide donors containing electron neutral to electron with-drawing substituents generally form weaker complexes with SnCl₄ aM exhibit maxima in continuous variation plots at a 1:1 ligand-to-metal ratio. Free ligand is evident in these solutions even at ligand-to-metal ratios as low as 1:3. Formation plots for these complexes indicate the possibility that 1: 2 and 1:1 ligand to metal complexes exist in the concentration ranges studied. Ligands exhibiting this behaviour include the 4-chloro-, 4-nitro-, 3 and 4-acetyl-pyridine N-oxides and 2-pyridine methanol N-oxide.The complex of 2,6-1utidine N-oxide with SnCl₄ exhibits behaviour characteristic of the 1:1 complexes even though the substituents are electron releasing. This ligand contains the most sterically crowded N-O group in the series, however, and steric factors are invoked to explain this behavior.These results are rationalized in terms of an equilibrium model which includes the postulated existence of oxygen bridged dimers comprising a dominant species in solutions containing the 1:1 complexes. Some supporting ¹H NMR and polarographic data are also presented and discussed.