Structure of a Discrete 8:6 La(Iii): P-Sulfonatocalix[4]Arene Complex

Abstract

The crystal structure of a complex formed between La(III) and p-sulfonatocalix[4]arene is reported. The complex cristallizes in the monoclinic space group P2₁/n, a = 15.091(1), b = 28.550(3), c = 30.167(3) Å, β = 90.008(2)°, V = 12997(2) ų, ρ_calc. (g cm^?3) = 1.792, Z = 2. Refinement led to R₁ value of 0.0961 for 13930 unique reflections. It forms discrete units with 8 La(III) cations coordinated by 6 calixarene ligands. The calixarenes are organized in an up-down configuration, bridged by La(III), forming layers of 3 repeating calixarene units and channels along the a axis. The units are linked by hydrogen-bonds.     

Oxidation of Polyisoprene Popcorn Polymer. IV. Effect of Polymer Purity on Carbon Dioxide and Water Yields

Abstract

Recent oxidation studies on polysisoprene popcorn polymer have shown that the yields of volatile products are a function of the presence or absence of residual isoprene dimers on the polymer. In contrast to previously reported data, no carbon dioxide is detected when highly purified polymer is used. Also, the yields of water drop to approximately half the previously reported values. Quantitative data are presented for the production of water during the early stages of autoxidation. The reported data emphasize the possible errors that can occur when oxidation reaction mechanisms are based on the stoichiometry of volatile products produced from impure polymer samples.     

Bisthiourea: thermal and structural investigation

Bisthiourea derivatives 1,1′-(ethane-1,2-diyl)bis(3-phenylthiourea), 1,1′-(propane-1,3-diyl)bis(3-phenylthiourea), and 1,1′-(butane-1,4-diyl)bis(3-phenylthiourea) have been synthesized and characterized by IR, ¹H NMR, and ¹³C NMR. Suitable crystals of 1,1′-(propane-1,3-diyl)bis(3-phenylthiourea) were grown for single-crystal X-ray analysis and from the data it was observed that they organize into the P-1 space group. The thermal decomposition of these compounds has been studied by TG–DSC.     

Iridium-catalyzed asymmetric hydrogenation of olefins using TIQ phosphine–oxazoline ligands

A novel family of tetrahydroisoquinoline (TIQ) phosphine–oxazoline ligands and four corresponding iridium complexes have been developed and applied to the asymmetric hydrogenation of unfunctionalized olefins. The results showed that the best conversion rates were observed in up to 99% with an enantiomeric excess of 91%.     

An investigation of rare earth chloride mixtures: combinatorial optimisation for AA2024‐t3 corrosion inhibition

Rare earth (lanthanides) cations have demonstrated exceptional activity as cathodic corrosion inhibitors for aluminium alloys (AAs). While Ce is generally regarded as the most active, there have been reports of synergistic interactions between mixtures of rare earths, which show increased inhibitive activity. In this study a combinatorial experimental approach was used to evaluate the corrosion inhibition of four rare earth chlorides (Ce, La, Pr, Nd) singly and as mixtures. The estimation of corrosion currents using both potentiodynamic scans and electrochemical impedance spectroscopy (EIS) provided the quantification of corrosion inhibition. The results were then modelled to determine the best predicted inhibition activity. A partial least squares (PLS) regression indicated that the optimal response directly correlated with the amount of Ce present. From the regression analysis, Ce alone demonstrated the best inhibition activity, with the optimum mixture predicted to contain 100% Ce. The addition of La, Pr or Nd, was not observed to improve the inhibition activity. This study represents one of the first applications of combinatorial design to a fundamental question of corrosion inhibition. Copyright © 2010 John Wiley & Sons, Ltd.     

Functional polyisobutylenes via electrophilic cleavage/alkylation

Lewis‐acid catalyzed degradation of poly(isobutylene‐co‐isoprene) (butyl rubber) in the presence of an alkoxybenzene compound was studied as a new route toward low molecular weight multifunctional polyisobutylenes. Simultaneous cleavage and functionalization of butyl rubber was conducted at ?70 °C and ?40 °C under TiCl₄ or AlCl₃ catalysis in 60/40 hexane/methylene chloride cosolvents in the presence of (3‐bromopropoxy)benzene (BPB) for various times up to 24 h. The butyl rubber (EXXON? Butyl 365) possessed M _n = 1.91 × 10⁵ g/mol, PDI = 1.66 (GPC/MALLS), and 2.30 mol % isoprene units (nearly exclusively trans ?1,4). At ?70 °C with TiCl₄, molecular weight was reduced to various values within the range 7 to 11 × 10³ g/mol depending on conditions; lower BPB concentration produced lower molecular weight. However, the ratio of isobutylene repeat units to BPB units (IB/Q ) remained constant at about 43:1, which is approximately the same as the ratio of isobutylene to isoprene repeat units (IB/IP) in the starting butyl rubber (42.5:1). At ?40 °C with TiCl₄, molecular weight was reduced to about 5 × 10³ g/mol, and IB/Q was reduced below IB/IP, indicating nearly a difunctional telechelic structure. AlCl₃ was a more active catalyst and produced results similar to TiCl₄ at ?40 °C, even when used at seven times lower concentration. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1991–1997     

Triple Helical Ir(ppy)3 Phenylene Cage Prepared by Diol-Mediated Benzannulation: Synthesis,Resolution, Absolute Stereochemistry and Photophysical Properties

Cyclometalation of a triple helical N-doped phenylene cage prepared by ruthenium(0)-catalyzed diol–diene benzannulation delivers a chiral, conformationally constrained Ir(ppy)₃ analogue. Like the parent complex, fac-Ir(ppy)₃, the iridium-containing PAH-cage is phosphorescent, but displays enhanced resistance to oxygen quenching.     

The Distinct Conformational Landscapes of 4S-Substituted Prolines That Promote an endo Ring Pucker

4-Substitution on proline directly impacts protein main chain conformational preferences. The structural effects of N-acyl substitution and of 4-substitution were examined by NMR spectroscopy and X-ray crystallography on minimal molecules with a proline 4S-nitrobenzoate. The effects of N-acyl substitution on conformation were attenuated in the 4S-nitrobenzoate context, due to the minimal role of the n→π* interaction in stabilizing extended conformations. By X-ray crystallography, an extended conformation was observed for most molecules. The formyl derivative adopted a δ conformation that is observed at the i+2 position of β-turns. Computational analysis indicated that the structures observed crystallographically represent the inherent conformational preferences of 4S-substituted prolines with electron-withdrawing 4-position substituents. The divergent conformational preferences of 4R- and 4S-substituted prolines suggest their wider structure-specific application in molecular design. In particular, the proline endo ring pucker favored by 4S-substituted prolines uniquely promotes the δ conformation [(ϕ, ψ) ≈(−80°, 0°)] found in β-turns. In contrast to other acyl capping groups, the pivaloyl group strongly promoted trans amide bond and polyproline II helix conformation, with a close n→π* interaction in the crystalline state, despite the endo ring pucker, suggesting its special capabilities in promoting compact conformations in ϕ due to its strongly electron-donating character.