Synthesis of Cis-Cisoid or Cis-Transoid Poly(Phenyl-Acetylene)s Having One or Two Carbamate Groups as Oxygen Permeation Membrane Materials

Three new phenylacetylene monomers having one or two carbamate groups were synthesized and polymerized by using (Rh(norbornadiene)Cl)2 as an initiator. The resulting polymers had very high average molecular weights (Mw) of 1.4–4.8 × 106, with different solubility and membrane-forming abilities. The polymer having two carbamate groups and no hydroxy groups in the monomer unit showed the best solubility and membrane-forming ability among the three polymers. In addition, the oxygen permeability coefficient of the membrane was more than 135 times higher than that of a polymer having no carbamate groups and two hydroxy groups in the monomer unit with maintaining similar oxygen permselectivity. A better performance in membrane-forming ability and oxygen permeability may be caused by a more extended and flexible cis-transoid conformation and lower polarity. On the other hand, the other two new polymers having one carbamate group and two hydroxy groups in the monomer unit showed lower performances in membrane-forming abilities and oxygen permeabilities. It may be caused by a very tight cis-cisoid conformation, which was maintained by intramolecular hydrogen bonds.

Synthesis and Structure of Methylsulfanyl Derivatives of Nickel Bis(Dicarbollide)

Symmetrically and unsymmetrically substituted methylsulfanyl derivatives of nickel(III) bis(dicarbollide) (Bu4N)[8,8′-(MeS)2-3,3′-Ni(1,2-C2B9H10)2], (Bu4N)[4,4′-(MeS)2-3,3′-Ni(1,2-C2B9H10)2], and (Bu4N)[4,7′-(MeS)2-3,3′-Ni(1,2-C2B9H10)2] were synthesized, starting from [Ni(acac)2]3 and the corresponding methylsulfanyl derivatives of nido-carborane (Bu4N)[10-MeS-7,8-C2B9H11] and (Bu4N)[10-MeS-7,8-C2B9H11]. Structures of the synthesized metallacarboranes were studied by single-crystal X-ray diffraction and quantum chemical calculations. The symmetrically substituted 8,8′-isomer adopts transoid conformation stabilized by two pairs of intramolecular C–H···S hydrogen bonds between the dicarbollide ligands. The unsymmetrically substituted 4,7′-isomer adopts gauche conformation, which is stabilized by two nonequivalent C–H···S hydrogen bonds and one short chalcogen B–H···S bond (2.53 Å, −1.4 kcal/mol). The gauche conformation was found to be also preferred for the 4,7′-isomer.

Electrochemical studies of grid and linear type M^2+ (M=Zn, Cd and Pb) complexes of a bis-(hydrazone) bearing two symmetric carboxylic groups

Herein we present the preparation of a bis-(hydrazone) containing a pyridine-pyrimidine-pyridine framework. This compound can be visualized as a double arm system able of coordinating two metal ions in a terpyridine-like manner. By NMR (1D and 2D) it was determined a transoid conformation and an E configuration around the two imine double bonds. Complexation with M2+ (M = Zn, Cd, and Pb) ions resulted in grid and linear type structures which were studied by cyclic and squared wave voltammetry at different temperatures. No linear correlations of the redox potentials as a function of temperature were observed. The latter is likely due to rearrangements in the structure or to spin crossover events. The present results deserve further studies on the electronic properties of these types of compounds for the development of smart materials.

Septipyridines as conformationally controlled substitutes for inaccessible bis(terpyridine)-derived oligopyridines in two-dimensional self-assembly

The position of the peripheral nitrogen atoms in bis(terpyridine)-derived oligopyridines (BTPs) has a strong impact on their self-assembly behavior at the liquid/HOPG (highly oriented pyrolytic graphite) interface. The intermolecular hydrogen bonding interactions in these peripheral pyridine units show specific 2D structures for each BTP isomer. From nine possible constitutional isomers only four have been described in the literature. The synthesis and self-assembling behavior of an additional isomer is presented here, but the remaining four members of the series are synthetically inaccessible. The self-assembling properties of three of the missing four BTP isomers can be mimicked by making use of the energetically preferred N–C–C–N transoid conformation between 2,2'-bipyridine subunits in a new class of so-called septipyridines. The structures are investigated by scanning tunneling microscopy (STM) and a combination of force-field and first-principles electronic structure calculations.

1,1′-Di(tert-butyl)metallocenium Cations. The X-Ray Crystal Structures of [M(C5H4tBu)2]PF6 (M = Fe, Co) and [Co (C5H4t Bu)2]2CoCl4

The hexafluorophosphate salts [Fe(C5H4tBu)2]PF6 (1) and [Co(C5 H4 tBu)2]PF6 (2) crystallize in isotypic structures with centrosymmetric cations which have a staggered (transoid) conformation of the exactly parallel ring ligands (conformational angle τ = 180°). The tetrachlorocobaltate salt, [Co(C5H4tBu)2 ]2 CoCl4 (3), contains one almost eclipsed (τ = 140.4°) and one almost staggered (τ = 101.4°) cobaltocenium cation; in both cases, the cyclopentadienyl ring planes are slightly inclined (by α = 5.4° and 4.1°, respectively) to give more room to the tert-butyl substituents which are bent away from the metal in all three complexes 1 - 3

Conformations and charge distributions in fluoronitrosoethylenes and nitrosoethylene

The optimized structures, bond orders, and electrostatic potentials for both transoid and cisoid fluoronitrosoethylenes and nitrosoethylene have been calculated by abinitio self-consistent-field molecular orbital procedure. The transoid structures are found to be of lower energy than the cisoids. Analyses of the calculated bond orders show that the C—C bond energy compares well with that of ethylene and the C—N bond energy with that of ethylamine, and therefore the contributions from ionic resonance structures are predicted to be small. The calculated electrostatic potential contour maps show that the presence of the nitroso group completely eliminates the negative potential region associated with the C—C double bond, thus rendering it less susceptible to electrophilic attack. Analyses of the values and relative locations of positive electrostatic potentials correctly predict that the nucleophilic addition to β-carbon is favoured when in the transoid conformation. Keywords: conformation, charge distribution, fluoronitrosoethylenes, nitrosoethylenes.

NMR-spektroskopische Untersuchung des Problems der Valenzisomerie zwischen 1,2-Dithiin und (Z)-But-2-en-1,4-dithion / NMR Spectroscopic Investigation Concerning the Problem of Valence Isomerism between 1,2-Dithiine and (Z)-But-2-ene-1,4-dithione

3,6-Diaryl-1,2-dithiines and their precursors, (Z,Z)-1,4-bis(organylthio)-buta-1,3-dienes, are investigated by 1H and 13C NMR spectroscopy. The chemical shifts and coupling constants, which are relevant to the investigated problem, are determined and assigned, respectively, by different techniques (shift increments, spectrum simulation, heteronuclear 2D J-resolved and heteronuclear shift correlated 2D NMR spectra, anomalous off-resonance splittings and selective decoupling experiments). The NMR parameters are discussed in relation to the molecular structure. The 13C shift values prove the ring structure of 1,2-dithiines and exclude existence of the valence isomer (Z)-but-2-ene-1,4-dithione (absence of thiocarbonyl resonances). The vicinal 1H,1H coupling constants of the C4 unit of the investigated compounds verify (1) the (Z,Z) configuration of the organylthio groups in 1,4 position of butadiene, (2) the s-transoid conformation of acyclic butadienes and (3) the forced s-cis structure in the cyclic 1,2-dithiines.