Macrocyclic aromatic polysulfones and sulfide-sulfones: synthesis and structural characterisation of molecular pentagons and rectangles

Cyclo-condensation of arylenedithiols with bis(4-chlorophenylenesulfone)s under pseudo-high-dilution conditions affords macrocyclic aromatic sulfide-sulfones which are readily oxidised to all-sulfone-linked macrocycles. The cyclic pentamer of poly(1,4-phenylenesulfone) and cyclic dimer of poly(1,4-phenylenesulfonyl-4,4'-biphenylenesulfone) have been isolated and characterised.

Unexpectedly superior enantioselectivity for trans-stilbene cis-dihydroxylation over anchored triosmium carbonyl species in confined Al-MCM-41 channels

Superior enantioselectivity in the dihydroxylation of trans-stilbene catalysed by anchored triosmium carbonyl species without using a chiral modifier is observed inside sterically congested MCM-41 channels; this effect is more pronounced through the introduction of surface Al sites into the silicate.

Dinuclear copper and zinc complexes of a hexaazamacrocycle containing p-xylyl spacers and bridging anions: theoretical and spectroscopic studies

The hexaazamacrocycle 7,22-dimethyl-3,7,11,18,22,26-hexaazatricyclo[26.2.2.2(13,16)] tetratriaconta-1(30), 13,15,28,31,33- hexaene (Me-2[30] pbz(2)N(6)) was synthesized and characterised by single crystal X-ray diffraction. The macrocycle adopts a conformation with the two aromatic rings almost parallel at a distance of ca. 4.24 Angstrom, but displaced relative to each other by ca. 1.51 Angstrom. The protonation constants of this compound and the stability constants of its complexes with Cu2+ and Zn2+, were determined in water - methanol (9 : 1 v/v) at 25 degreesC with ionic strength 0.10 mol dm(-3) in KCl. The potentiometric and spectroscopic studies (NMR of zinc, cadmium and lead complexes, and EPR of the copper complexes) indicate the formation of only dinuclear complexes. The association constants of the dinuclear copper complex with anions ( thiocyanate, terephthalate and glyphosate) and neutral molecules (1,4-benzenedimethanol, p-xylylenediamine and terephthalic acid) were determined at 20 degreesC in methanol. The structural preferences of this ligand and of its dinuclear copper(II) complex with a variety of bridging ligands were evaluated theoretically by molecular mechanics calculations (MM) and molecular dynamics (MD) using quenching techniques.

Aromatic-aromatic interaction between metallacycle and phenyl ring

The X-ray crystal structure of [CuL2]ClO4 where L is the 1:1 condensate of benzil-monohydrazone and 2-pyridinecarboxalde-hyde, reveals unprecedented pi - pi interaction between the metallacycles and phenyl rings. The interaction is intramolecular. (C) 2003 Elsevier Science B.V. All rights reserved.

Crystal and molecular structure of the thioether-analogue of PEEK from X-ray powder data and diffraction-modelling

Analysis of X-ray powder data for the melt-crystallisable aromatic poly(thioether thioether ketone) [-S-Ar-S-Ar-CO-Ar](n), ('PTTK', Ar= 1,4-phenylene), reveals that it adopts a crystal structure very different from that established for its ether-analogue PEEK. Molecular modelling and diffraction-simulation studies of PTTK show that the structure of this polymer is analogous to that of melt-crystallised poly(thioetherketone) [-SAr-CO-Ar](n) in which the carbonyl linkages in symmetry-related chains are aligned anti-parallel to one another. and that these bridging units are crystallographically interchangeable. The final model for the crystal structure of PTTK is thus disordered, in the monoclinic space group 121a (two chains per unit cell), with cell dimensions a = 7.83, b = 6.06, c = 10.35 angstrom, beta = 93.47 degrees. (c) 2005 Elsevier Ltd. All rights reserved.

Dithioacetalisation of PEEK: a general technique for the solubilisation and characterisation of semi-crystalline aromatic polyketones

The family of semi-crystalline, aromatic, high-temperature thermoplastics known as poly(ether-ketone)s are insoluble in conventional organic solvents, but undergo completely general and quantitatively reversible reactions with alkanedithiols in strong acid media, to give soluble poly(dithioacetal)s, which are readily characterisable by GPC and light scattering techniques.

Recognition of sequence-information in synthetic copolymer chains by a conformationally-constrained tweezer molecule

A novel type of tweezer molecule containing electron-rich 2-pyrenyloxy arms has been designed to exploit intramolecular hydrogen bonding in stabilising a preferred conformation for supramolecular complexation to complementary sequences in aromatic copolyimides. This tweezer-conformation is demonstrated by single-crystal X-ray analyses of the tweezer molecule itself and of its complex with an aromatic diimide model-compound. In terms of its ability to bind selectively to polyimide chains, the new tweezer molecule shows very high sensitivity to sequence effects. Thus, even low concentrations of tweezer relative to diimide units (<2.5 mol%) are sufficient to produce dramatic, sequence-related splittings of the pyromellitimide proton NMR resonances. These induced resonance-shifts arise from ring-current shielding of pyromellitimide protons by the pyrenyloxy arms of the tweezer-molecule, and the magnitude of such shielding is a function of the tweezer-binding constant for any particular monomer sequence. Recognition of both short-range and long-range sequences is observed, the latter arising from cumulative ring-current shielding of diimide protons by tweezer molecules binding at multiple adjacent sites on the copolymer chain.

Principles of sequence-recognition in aromatic polyimides

Pyrene-based molecular tweezers show sequence-specific binding to aromatic polyimides through sterically-controlled donor-acceptor pi-stacking and hydrogen bonding; H-1 NMR spectra of tweezer-complexes with polyimides having different sequence-restrictions show conclusively that the detection of long range sequence-information results from multiple tweezer-binding at adjacent imide residues.

Microfabrication of high-performance aromatic polymers as nanotubes or fibrils by in situ ring-opening polymerisation of macrocyclic precursors

Melt-phase nucleophilic ring-opening polymerisation of macrocyclic aromatic ethers and thioethers at high temperatures within the cylindrical pores of an anodic-alumina membrane, followed by dissolution of the template, enables replication of the membrane's internal pore structure and so affords high-performance aromatic polymers with well-defined fibrillar or tubular morphologies.

Spontaneous ring-opening polymerization of macrocyclic aromatic thioether ketones under transient high-temperature conditions

Spontaneous ring-opening polymerization of macrocyclic aromatic thioether ketones [-1,4-SC6H4CO-C6H4-](n) (n = 3 and 4), in which the thioether linkages are para to the ketone, occurs during rapid, transient heating to 480degreesC, to afford a soluble, semi-crystalline poly(thioether ketone) of high molar mass (eta(inh) > 1.0 dL . g(-1)). Corresponding macrocyclic ether ketone, and a macrocyclic thioether ether ketone in which the thioether linkage is para to the ether rather than to the ketone, show no evidence of polymerization under analogous conditions.

A hexadecanuclear copper(I)-copper(II) mixed-valence compound: structure, magnetic properties, intervalence charge transfer, EPR, and NMR

Hexadecanuclear copper mixed-valence complex 2 containing 10 Cu-II, centers and 6 Cu-I centers was isolated with N,O donor ligands. From the X-ray crystal structure, 2 was found to contain a centrosymmetric dimeric cation - each monomeric unit composed of eight copper centers. It displays a very broad and weak intervalence charge-transfer band around 1100 nm at room temperature in the solid state. Variable-temperature magnetic susceptibility measurements indicate an S = 1/2 ground state for half of 2, explicitly, each Cu-8 moiety has a g value around 2.26. Complex 2 was examined by NMR spectroscopy at room temperature in solution and by EPR at low temperature; the data indicates that the valence is delocalized in 2 at room temperature but localized at low temperature. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Observation of carbonyl oxygen-pi interaction in a metal complex

X-ray crystallography shows that [Ag2L2(H2O)(2)](BF4)(2) where L is a 1:1 condensate of 1,2-diphenylethane-1,2-dione and 2-(2-aminoethyl pyridine), contains an Ag(I)-Ag(I) bond of length 2.979(2) angstrom and an angular, intraligand interaction of the keto O with the pi cloud of the pyridine moiety (O-pyridine centroid = 3.12 angstrom). Model MP2/6-311++G(d,p) calculations indicate that the observed lone pair-pi type interaction is stabilising and not merely a tolerated short contact. (C) 2008 Elsevier B.V. All rights reserved.

Synthesis of chiral 3,4,5,6-tetrahydro-1,4-thiazin-2-ones (thiamorpholin-2-ones)-novel heterocycles possessing enhanced carbonyl electrophilicity over their oxygen counterparts

We report herein the first synthesis of chiral derivatives possessing the 1,4-thiazinone core. As predicted, the thiolactone is more susceptible to nucleophilic attack than the equivalent lactone system.

Ruthenium complexes of C,C '-bis(ethynyl)carboranes: an investigation of electronic interactions mediated by spherical pseudo-aromatic spacers

The complexes [Ru(1-C=C-1,10-C2B8H9)(dppe)Cp*] (3a), [Ru(1-C C-1,12-C2B10H11)(dppe)-Cp*] (3b), [{Ru(dppe)Cp*}(2){mu-1,10-(C C)(2)-1,10-C2B8H8}] (4a) and [{Ru(dppe)Cp*}(2){mu-1,12-(C C)2- 1,12-C2B10-H-10}] (4b), which form a representative series of mono- and bimetallic acetylide complexes featuring 10- and 12-vertex carboranes embedded within the dethynyl bridging ligand, have been prepared and structurally characterized. In addition, these compounds have been examined spectroscopically (UV-is-NIR, IR) in all accessible redox states. The significant separation of the two, one-electron anodic waves observed in the cyclic voltammograms of the bimetallic complexes 4a and 4b is largely independent of the nature of the electrolyte and is attributed to stabilization of the intermediate redox products [4a](+) and [4b](+) through interactions between the metal centers across a distance of ca. 12.5 angstrom. The mono-oxidized bimetallic complexes (4a](+) and [4b](+) exhibit spectroscopic properties consistent with a description of these species in terms of valence-localized (class II) mixed-valence compounds, including a unique low-energy electronic absorption band, attributed to an, IVCT-type transition that tails into the IR region. DFT calculations with model systems [4a-H](+) and [4b-H](+) featuring simplified ligand sets reproduce the observed spectroscopic data and localized electronic structures for the mixed-valence cations [4a](+) and [4b](+).