Ethynyl pi-extended 2,5-diphenyl-1,3,4-oxadiazoles and 2-phenyl 5-(2-thienyl)-1,3,4-oxadiazoles: synthesis, X-ray crystal structures and optical properties

2-(4-tert-Butylphenyl)-5-(4-ethynylphenyl)-1,3,4-oxadiazole reacts with a series of heteroaryl iodides under standard Sonogashira cross-coupling conditions (Pd[PPh(3)](2)Cl(2), CuI, triethylamine, THF) to yield products 2a-g in 40-79% yields (heteroaryl = 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrazyl, 5-bromo-2-pyrimidyl, 2-thienyl and 3-thienyl, respectively). Compound 2f was lithiated followed by electrophilic iodination (BuLi, perfluorohexyl iodide) to give 3, which by a two-step sequence gave the terminal ethynylthienyl derivative 5. Conversion of 5 into the terminal ethynylaldehyde derivative 7, via acetal derivative 6, proceeded in high yield. Starting from 2-iodo-5-methoxycarbonylthiophene, a five-step sequence afforded 2-(4-tert-butylphenyl)-5-(4-ethynylthienyl)-1,3,4-oxadiazole 13 (13% overall yield). Reactions of 13 gave terminal pyridyl, pyrazyl, pyrimidyl and thienyl derivatives, analogous to those obtained from 1. Two-fold reaction of 13 with 2,5-diiodothiophene gave the bis(ethynylthienyl)thiophene derivative 15 (30% yield). Solution UV-Vis absorption and photoluminescence spectra establish that replacement of the phenyl ring in the 2,5-diphenyl-1,3,4-oxadiazole series 2a-g by a thienyl ring [i.e. the 2-phenyl-5-(2-thienyl)-1,3,4-oxadiazole series 14a-g] leads to a red shift in the lowest energy band in both the absorption spectra and emission spectra. The X-ray crystal structures of compounds 2d, 2g, 5 and 14d.CHCl(3) reveal that the molecular structures are approximately planar although there are substantial differences in the conformations.     

Effects of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles on the temperature range of liquid crystalline blue phases: a systematic study

Four series of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles with different lateral substituents and terminal alkoxy chain length were synthesised and characterised. Then, all these bent-shaped compounds were separately doped into the blue phase (BP) liquid crystal host and their effects on the BP range of the host were investigated, which shows that the BP ranges varied greatly with the difference in the structure of 2,5-disubstituted 1,3,4-oxadiazoles and their doped concentration. Moreover, in order to explore the influence of the inherent molecular geometry and properties of the bent-shaped molecules on the stability of BPs, the molecular structures of all the compounds were studied by using the theory of density functional theory, and the optimised structural parameters of the molecules were calculated at the B3LYP/6–31G* level.     

Remarkably stable iron porphyrins bearing nonheteroatom-stabilized carbene or (alkoxycarbonyl)carbenes: isolation,X-ray crystal structures,and carbon atom transfer reactions with hydrocarbons

Reactions of [Fe(TPFPP)] (TPFPP = meso-tetrakis(pentafluorophenyl)porphyrinato dianion) with diazo compounds N(2)C(Ph)R (R = Ph, CO(2)Et, CO(2)CH(2)CH=CH(2)) afforded [Fe(TPFPP)(C(Ph)R)] (R = Ph (1), CO(2)Et (2), CO(2)CH(2)CH=CH(2) (3)) in 65-70% yields. Treatment of 1 with N-methylimidazole (MeIm) gave the adduct [Fe(TPFPP)(CPh(2))(MeIm)] (4) in 65% yield. These new iron porphyrin carbene complexes were characterized by NMR and UV-vis spectroscopy, mass spectrometry, and elemental analyses. X-ray crystal structure determinations of 1.0.5C(6)H(6).0.5CH(2)Cl(2) and 4 reveal Fe=CPh(2) bond lengths of 1.767(3) (1) and 1.827(5) A (4), together with large ruffling distortions of the TPFPP macrocycle. Complexes 2 and 4 are reactive toward styrene, affording the corresponding cyclopropanes in 82 and 53% yields, respectively. Complex 1 is an active catalyst for both intermolecular cyclopropanation of styrenes with ethyl diazoacetate and intramolecular cyclopropanation of allylic diazoacetates. Reactions of 2 and 4 with cyclohexene or cumene produced allylic or benzylic C-H insertion products in up to 83% yield.     

Synthesis of cyclomanganated complexes derived from 2,5-diphenyl-1,3,4-oxadiazole and their reactivity with respect to 1,1-diphenyldiazomethane: Evidence for a fluxional trihaptobenzylic coordination mode

The cyclometallation of 2,5-diphenyl-1,3,4-oxadiazole with benzylpentacarbonylmanganese afforded the related mono- and binuclear complexes. The thermolytic coupling of 1,1-diphenyldiazomethane with monometallated 2,5-diphenyl-1,3,4-oxadiazole afforded substantial amounts of a new trihaptobenzylic complex. In the solid state, an X-ray diffraction analysis confirmed the coordination of manganese metal to one of the phenyl groups introduced by the 1,1-diphenyldiazomethane and to one of ligand’s nitrogen centre. In solution, this trihaptobenzylic complex displays a fluxionality which is assumed to be related to the equilibration of its helical Λ and Δ enantiomers.     

Synthetic approaches and pharmacological activity of 1,3,4-oxadiazoles: a review of the literature from 2000-2012

This review provides readers with an overview of the main synthetic methodologies for 1,3,4-oxadiazole derivatives, and of their broad spectrum of pharmacological activities as reported over the past twelve years.     

Cyclooctene epoxidation with H2O2 and single crystal X-ray determined crystal structures of new molybdenum and tungsten catalysts bearing the hydrophilic ligand hydroxymethyldiphenylphosphine oxide

The dioxo molybdenum and tungsten complexes MoO₂Cl₂(OPPh₂CH₂OH)₂ and WO₂Cl₂(OPPh₂CH₂OH)₂ have been synthesized and characterized by FT-IR, ¹H and ³¹P NMR. Their structures, as determined by single crystal X-ray diffraction analysis, reveal distorted octahedral geometries with cis terminal oxygen atoms, trans Cl ligands and that the hydroxymethyldiphenylphosphine oxide ligands coordinate through the oxygen atom bonded to the P atom. Both of the compounds are studied as catalysts for the epoxidation of cis-cyclooctene in the presence of hydrogen peroxide as a source of oxygen. Both complexes showed good activity and very high selectivity for the formation of cyclooctene oxide.     

Cyclodextrin cavity size effect on the complexation and rotational dynamics of the laser dye 2,5-diphenyl-1,3,4-oxadiazole: from singly occupied complexes to their nanotubular self-assemblies

The general complexation scheme as well as the dynamic features of the supramolecular structures resulting from the interaction of the laser dye 2,5-diphenyl-1,3,4-oxadiazole (PPD) with the naturally occurring alpha-, beta-, and gamma-cyclodextrins in water are studied by means of fluorescence spectroscopy, both steady-state (SS) and time-resolved (TR). PPD interacts weakly, from a thermodynamic point of view, with alpha-cyclodextrin (alpha-CD), forming 1:1 complexes with an association constant of K(11) = 85 +/- 4 M(-1). However, the local motion of the substrate (PPD) with respect to the ligand (CD) in the complexed form is hindered; namely, dynamically, they are strongly coupled and only a global tumbling motion, = 370 +/- 30 ps, of the whole adduct is observed. The next homologue beta-CD also forms 1:1 entities with PPD, but although the binding strength of reactants (K(11) = 682 +/- 60 M(-1)) is almost an order of magnitude greater than the former case with the alpha-CD, these are dynamically weakly coupled. In fact, two independent motions are detected: one is that of the whole nanostructure motion (1:1, PPD/beta-CD) with a global rotational relaxation time of = 480 +/- 30 ps, and the other is an internal librational motion of the dye inside the host cavity with an average angular displacement of theta approximately 27 degrees . Finally, the interaction of PPD with the wider and more flexible cavity of the gamma-CD "triggers" a self-associative scheme of the initially formed supramolecular building blocks, namely, singly occupied complexes, leading to the formation of nanotubular superstructures. It is found that these linear arrays are constituted from more than 17 gamma-CD units which are held together with the aid of dimers of PPD. Interestingly, our results supported that two distinct dimeric forms of PPD play the role of the "shaft" between adjacent cyclodextrin units. The topology of the dimers in the interlinking space of gamma-CD units is such that PPD molecules are held in suitable proximity, resulting, upon excitation, in the observation of dual excimer emission.     

X-ray structural investigation of the adduct of 1,3-di(tert-butyl)-2,4-di(tert-butylamido)diazadiphosphetidine with carbon disulfide and 2,5-diphenyl-3-cyclohexyl-4-oxo-4-cyclohexylamido-1,3,4-oxazaphospholidine

An x-ray structural investigation of the products of the reactions of 1,3-di(tert-butyl)-2,4-di(tert-butylamido)diazadiphosphetidine and 1,3-dicyclohexyl-2,4-di(cyclohexylamido)diazadiphosphetidine with carbon disulfide and benzaldehyde, respectively, has been carried out (Mo, 2006 and 1484 reflections, R=0.038 and 0.083). It has been shown that in the former reaction the four-membered P₂N₂ ring is maintained, and a new exocyclic bond appears between one of its P atoms and the carbon atom of carbon disulfide with the formation of a zwitterionic adduct with the formula C₁₅H₃₈N₄P₂·CS₂. In the latter case the P₂N₂ ring is opened, and a new five-membered heterocycle is closed with the formation of 2,5-diphenyl-3-cyclohexyl-4-oxo-4-cyclohexylamido-1,3,4-oxazaphospholidine C₂₆H₃₅O₂N₂P. The geometric parameters of both molecules investigated have been analyzed in detail.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. A. N. Nesmeyanov Institute of Organometallic Compounds, Academy of Sciences of the USSR. Institute of Organic Chemistry, Academy of Sciences of the Ukrainian SSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 133–138, March–April, 1991.     

Reactive dications: the superacid-catalyzed reactions of alkynes bearing adjacent N-heterocycles or amine groups

A variety of aminoalkynes and related heterocycles are reacted in the Bronsted superacid CF(3)SO(3)H (triflic acid), and products are obtained in generally good yields (69-99%) from Friedel-Crafts-type reactions. The reactions are consistent with the formation of novel dicationic intermediates having a vinyl cationic site and an adjacent protonated N-heterocycle or ammonium cation.     

X-ray crystal structures of reduced rubrerythrin and its azide adduct: a structure-based mechanism for a non-heme diiron peroxidase

Rubrerythrin (Rbr) is a 44-kDa homodimeric protein, found in many air-sensitive bacteria and archaea, which contains a unique combination of a rubredoxin-like [Fe(SCys)(4)] site and a non-sulfur, oxo/dicarboxylato-bridged diiron site. The diiron site structure resembles those found in O2-activating diiron enzymes. However, Rbr instead appears to function as a hydrogen peroxide reductase (peroxidase). The diferrous site in all-ferrous Rbr (Rbr(red)) shows a much greater reactivity with H2O2 than does the diferric site in all-ferric Rbr (Rbr(ox)), but only the latter structure has been reported. Here we report the X-ray crystal structures of the recombinant Rbr(red) from the sulfate reducing bacterium, Desulfovibrio vulgaris, as well as its azide adduct (Rbr(red)N3). We have also redetermined the structure of Rbr(ox) to a higher resolution than previously reported. The structural differences between Rbr(ox) and Rbr(red) are localized entirely at the diiron site. The most striking structural change upon reduction of the diferric to the diferrous site of Rbr is a 1.8-A movement of one iron away from a unique glutamate carboxylate ligand and toward a trans-disposed histidine side chain, which replaces the glutamate as a ligand. This movement increases the inter-iron distance from 3.3 to 4 A. Rbr(red)N(3) shows this same iron movement and His-->Glu ligand replacement relative to Rbr(ox), and, in addition, an azide coordinated to the diiron site in a cis mu-1,3 fashion, replacing two solvent ligands in Rbr(red). Relative to those in O2-activating enzymes, the bridging carboxylate ligation of the Rbr diiron site is less flexible upon diferric/diferrous interconversion. The diferrous site is also much more rigid, symmetrical, and solvent-exposed than those in O2-activating enzymes. On the basis of these unique structural features, a mechanism is proposed for facile reduction of hydrogen peroxide by Rbr involving a cis mu-eta(2) H2O2 diferrous intermediate.     

N-heterocyclic carbene adducts of cyclopalladated ferrocenylpyridine containing chloride or iodide anions: synthesis, crystal structures and application in the coupling of terminal alkynes with arylboronic acids

Two air-stable N-heterocyclic carbene (NHC) adducts of cyclopalladated ferrocenylpyridine containing chloride or iodide anions 2–3 have been easily prepared from the bridge-splitting reaction of the palladacyclic dimer 1 and anion exchange reaction, respectively. They were characterized by elemental analysis, IR, ¹H, and ¹³C NMR. Additionally, the structures of these complexes were determined by single-crystal X-ray analysis. These adducts have been successfully applied to the coupling of terminal alkynes with arylboronic acids under atmospheric conditions.     

Using nucleophilic substitution reactions to understand how a remote alkyl or alkoxy substituent influences the conformation of eight-membered ring oxocarbenium ions

[reaction: see text] A remote alkoxy substituent strongly stabilizes one particular conformer of an eight-membered ring oxocarbenium ion by a through-space electrostatic effect. X-ray crystallographic analysis of a crystalline derivative proves that kinetically controlled nucleophilic substitution favors the 1,4-trans product. Nucleophilic substitution of the corresponding alkyl-substituted acetate, however, is unselective. A computational model has been developed and experimentally validated to predict the low-energy conformers of C3-, C4-, or C5-alkyl- or alkoxy-substituted eight-membered ring oxocarbenium ions.     

Chiral crystalline hosts derived from lactic acid.* X-ray crystal structures of optically resolved and racemic host compound 1,1-diphenyl-1,2-propanediol and a 2:1 complex between optically resolved host and 3-picoline

Abstract

The X-ray crystal structures of racemic (1) and S-1,1-diphenyl-1,2-propanediol (2), and of a 2:1 inclusion complex (3) of 2 with 3-picoline are reported. Three different binding schemes characterize the packing of these structures. Only one of the two hydroxy groups (that which is not related to the asymmetric carbon) is involved in O-H…O hydrogen bonds responsible for the formation of dimers and chains in 1 and 2, leaving the other OH group for stabilization of dimers through OH…phenyl interactions in 1 or free of interactions in 2. In the crystal structure of the chiral complex 3, the hydroxy groups link the two independent host molecules, A and B, the 3-picoline guest to the B host molecule, and a remaining one forms H-bonded chains along the c axis.     

X‐ray crystal structures and MMA polymerization of cadmium(II) complexes with bidentate pyrazole ligands: the formation of monomers or dimers as a function of a methyl substituent on the pyrazole and aniline rings

The reaction of CdBr₂·4H₂O with ancillary ligands, N,N‐bis(1H‐pyrazolyl‐1‐methyl)aniline ( L₁ ), N,N‐bis(1H‐pyrazolyl‐1‐methyl)‐p‐methylaniline ( L₂ ), N,N‐bis(1H‐pyrazolyl‐1‐methyl)‐3,5‐dimethylaniline ( L₃ ), N,N‐bis(3,5‐dimethyl‐1H‐pyrazolyl‐1‐methyl)aniline ( L₄ ) and N,N‐bis(1H‐pyrazolyl‐1‐methyl)‐2,6‐dimethylaniline ( L₅ ) in ethanol yields novel Cd(II) bromide complexes, [L₁CdBr₂]₂ , [L₂CdBr₂]₂ , [L₃CdBr₂]₂ , [L₄CdBr₂] and [L₅CdBr₂] . The X‐ray crystal structures of [L₁CdBr₂]₂ , [L₂CdBr₂]₂ and [L₃CdBr₂]₂ reveal a bromo‐bridged dimeric species with crystallographic inversion symmetry. Conversely, [L₄CdBr₂] and [L₅CdBr₂] exist as monomeric complexes, presumably due to the steric hindrance between the methyl substituents of the two pyrazole groups in the ligand and cadmium centre for [L₄CdBr₂] , and crowding around the cadmium metal by methyl substituents on the aniline residue in the ligand for [L₅CdBr₂] . The geometry at each Cd(II) centre for [L₁CdBr₂]₂ , [L₂CdBr₂]₂ and [L₃CdBr₂]₂ is best described as a distorted trigonal bipyramid. A distorted trigonal bipyramid is achieved in [L₄CdBr₂] by coordinative interaction of the nitrogen atom of the aniline unit and the cadmium atom with a σ plane of symmetry, based on the bond length of Cd―N_aniline (2.759(7) Å). [L₅CdBr₂] exists with a distorted tetrahedral geometry involving non‐coordination of the nitrogen atom of aniline and the Cd centre, resulting in the formation of an eight‐membered chelate ring. The catalytic activity of monomeric, five‐coordinated [L₄CdBr₂] in the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60°C resulted in a higher molecular weight and a narrower polydispersity index (PDI) than those obtained with dimeric [L_nCdBr₂]₂ (L_n = L₁ , L₂ , L₃ ) or monomeric tetrahedral [L₅CdBr₂] . Copyright © 2014 John Wiley & Sons, Ltd.     

Double Friedel-Crafts acylation reactions on the same ring of a metallocene: synthesis of a 2,5-diacetylphospharuthenocene

The synthetic outcome of the Friedel-Crafts acylation of 1',2',3,3',4,4',5'-heptamethylphospharuthenocene reflects the nature of the acylating agent, with alkanoyl anhydride/trifluoromethanesulfonic acid (TfOH) reagents giving monosubstitution at the phospholyl ring, whereas alkanoyl chloride/AlCl(3) gives 2,5-disubstitution. DFT calculations indicate that this unusual double acylation can be facilitated by the intervention of the phosphorus atom at an early stage in the reaction trajectory, with the acyl group being delivered from the phosphorus atom into the ring 2- or 2,5-positions.     

Primary and secondary phosphane complexes of metalloporphyrins: isolation, spectroscopy, and X-ray crystal structures of ruthenium and osmium porphyrins binding phenyl- or diphenylphosphane

[Ru(II)(por)(PH(n)Ph(3-n))2], [Os(II)(por)(CO)(PH(n)Ph(3-n))] (n=1, 2), and [Os(II)(F20-tpp){P(OH)Ph2}(PHPh2)] (F20-tpp=5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato dianion) were prepared from the reaction of [M(II)(por)(CO)] (M=Ru, Os) or [Os(VI)(por)O2] with the respective primary/secondary phosphane and characterized by 1H NMR, 31P NMR, UV/Vis, and IR spectroscopy, mass spectrometry, and elemental analysis. The reaction of [Os(VI)(por)O2] with PHPh2 also gave minor amounts of [Os(II)(por){P(OH)Ph2}2]. [Ru(II)(F20-tpp)(PH2Ph)2] exhibits a remarkable stability toward air and shows a reversible metal-centered oxidation couple at E(1/2)=0.39 V versus [Cp2Fe](+/0) in the cyclic voltammogram. The structures of [Ru(II)(F20-tpp)(PH2Ph)2] x 2CH2Cl2, [Ru(II)(4-Cl-tpp)(PHPh2)2] x 2CH2Cl2 (4-Cl-tpp=5,10,15,20-tetrakis(p-chlorophenyl)porphyrinato dianion), [Ru(II)(F20-tpp)(PHPh2)2], and [Os(II)(F20-tpp){P(OH)Ph2}2] were determined by X-ray crystallography and feature Ru-P distances of 2.3397(11)-2.3609(9) A and an Os-P distance of 2.369(2) A.