Polyethylenimine-impregnated mesoporous silica: effect of amine loading and surface alkyl chains on CO2 adsorption

Poly(ethyleneimine) (PEI) supported on pore-expanded MCM-41 whose surface is covered with a layer of long-alkyl chains was found to be a more efficient CO(2) adsorbent than PEI supported on the corresponding calcined silica and all PEI-impregnated materials reported in the literature. The layer of surface alkyl chains plays an important role in enhancing the dispersion of PEI, thus decreasing the diffusion resistance. It was also found that at low temperature, adsorbents with relatively low PEI contents are more efficient than their highly loaded counterparts because of the increased adsorption rate. Extensive CO(2) adsorption-desorption cycling showed that the use of humidified feed and purge gases affords materials with enhanced stability, despite limited loss due to amine evaporation.     

Catalytic Asymmetric Epoxidation of Aldehydes with Two VANOL‐Derived Chiral Borate Catalysts

A highly diastereo‐ and enantioselective method for the epoxidation of aldehydes with α‐diazoacetamides has been developed with two different borate ester catalysts of VANOL. Both catalytic systems are general for aromatic, aliphatic, and acetylenic aldehydes, giving high yields and inductions for nearly all cases. One borate ester catalyst has two molecules of VANOL and the other only one VANOL. Catalysts generated from BINOL and VAPOL are ineffective catalysts. An application is shown for access to the side‐chain of taxol.     

Tetranuclear azido-bridged copper(II) complex [Cu4(μ-salpn)2(μ1,1-N3)2(N3)2(H2O)2]: Synthesis,characterization and crystal structure

The reaction of salpnH₂ Schiff-base ligand (salpnH₂ = N,N′-bis(salicylidene)-1,3-propylenediamine) with Cu(NO₃)₂·3H₂O and a large excess of NaN₃ (1:2:8 molar ration), lead to the formation of [Cu₄(μ-salpn)₂(μ_1,1-N₃)₂(N₃)₂(H₂O)₂] (1), which has been successfully obtained and characterized by elemental analyses, IR spectroscopy and single-crystal X-ray diffraction. The strong absorption band at about 2000–2100 cm^?1 and at 1597 cm^?1 regions of the IR spectrum of 1 clearly proves the presence of the both end-on (EO) bridging and terminal azido ions and CN (azomethine) groups, respectively. Single-crystal X-ray analyses revealed that the copper atoms are bridged alternately by end-to-on (EO) azido and phenoxo-salpn ligands in the prepared tetranuclear copper(II) complex [Cu₄(μ-salpn)₂(μ_1,1-N₃)₂(N₃)₂(H₂O)₂] (1).     

Synthesis,Crystal Structure,Spectral and Thermal Studies of (<Emphasis Type="Italic">E</Emphasis>)-4-Dimethamino[(1-phenylethyl)iminomethyl]benzyne

Abstract  

Schiff-base compound (E)-4-dimethamino[(1-phenylethyl)iminomethyl]benzyne was synthesized and characterized by elemental analyses (CHN), FT-IR and ¹H-NMR spectroscopic techniques and thermogravimetric analyses (TG). Crystal structure of the title compound was obtained by single crystal X-ray diffraction. The title compound crystallizes in the monoclinic space group P2₁ with unit cell parameters: a = 8.5283(2), b = 6.0699(2), c = 13.6997(4) Ǻ, β = 91.471(2)°, V = 708.94(4) Ǻ³ and Z = 2.     

Immobilization of Keggin and Preyssler tungsten heteropolyacids on various functionalized silica

The Keggin and Preyssler tungsten heteropolyacids, H3PW12O40 and H15P5W30O110, have been immobilized on the inner surface of mesoporous MCM-41, fume silica and silica-gel by means of chemical bonding to aminosilane groups. The materials were characterized by FT-IR spectroscopy, low-angle XRD and BET surface area analysis. The tendencies of heteropolyacids adsorption in solution on functionalized silicas have been investigated by UV-vis. Among the functionalized silica materials, MCM-41 showed the largest amine to silica and the least heteropolyacid to silica ratios. The BET surface area revealed that in all three cases the surface area decreased after grafting amine group and anchoring of the HPAs clusters. Low-angle XRD analysis showed that by introducing HPA into functionalized MCM-41 the intensity of the main reflection decreased significantly.     

CO(2)-Induced Degradation of Amine-Containing Adsorbents: Reaction Products and Pathways

A comprehensive study was conducted to investigate the stability of a wide variety of mesoporous silica-supported amine-containing adsorbents in the presence of carbon dioxide under dry conditions. CO(2)-induced degradation of grafted primary and secondary monoamines (pMono, sMono), diamines with one primary and one secondary amines (Diamine) and triamine with one primary and two secondary amines (TRI) as well as different impregnated polyamines such as branched and linear polyethylenimine (BPEI and LPEI) and polyallylamine (PALL) was investigated using extensive CO(2) adsorption-desorption cycling as well as diffuse reflectance infrared Fourier transform (DRIFT) and (13)C CP MAS NMR measurements. Except for sMono, all other supported amines underwent significant deactivation in the presence of dry CO(2) under mild conditions. In all cases, the decrease in CO(2) uptake was associated with the formation of urea linkages at the expense of amine groups. The urea-containing species were identified, and the deactivation pathways were delineated.     

Synthesis, Spectroscopic and Thermal Studies of Zinc(II) Complexes with the Symmetrical Bidentate Schiff-Base Ligand (2,3-MeO-ba)2en: Crystal Structure of Zn((2,3-MeO-ba)2en)I2

Abstract  

Two zinc(II) complexes [ZnI₂((2,3-MeO-ba)₂en)] (1) and [ZnCl₂((2,3-MeO-ba)₂en)] (2), with the symmetrical bidentate Schiff-base ligand (2,3-MeO-ba)₂en [N,N′-bis(2,3-dimethoxybenzylidene)-1,2-diaminoethane] have been synthesized and characterized by elemental analyses (CHN), FT-IR and ¹H-NMR spectroscopy. The thermal behaviors of these complexes were studied using thermogravimetry in order to evaluate their thermal stability and thermal decomposition pathways. The crystal structure of [ZnI₂((2,3-MeO-ba)₂en)] (1) was determined from single-crystal X-ray diffraction. The coordination polyhedron about the zinc(II) center in the complex 1 is best described as a distorted tetrahedron.     

Direct Synthesis of PbO Nanoparticles From a Lead(II) Nano Coordination Polymer Precursor: Synthesis,Crystal Structure,and DFT Calculations of [Pb2(dmp)2(μ‐N3)2(μ‐ClO4)2]n with the First Pb2‐(μ‐ClO4)2 Unit

Nanostructures of a new coordination polymer of divalent lead with the ligand 2, 9‐dimethyl‐1, 10‐phenanthroline (dmp) containing the first Pb₂‐(μ‐ClO₄)₂ motif, [Pb₂(dmp)₂(μ‐N₃)₂(μ‐ClO₄)₂]_n ( 1 ), was synthesized by a sonochemical method that produces the coordination polymers at nano size. The new nanostructure was characterized by scanning electron microscopy, X‐ray powder diffraction, IR, ¹H NMR and ¹³C NMR spectroscopy, and elemental analysis. Compound 1 was structurally characterized by single‐crystal X‐ray diffraction and the single‐crystal X‐ray data shows that the coordination number of Pb^II ions is six, (PbN₄O₂), with two N‐donor atoms from aza‐aromatic base ligands and four O‐donors from two perchlorate anions and two N‐donors from two azide anions. It has a “stereo‐chemically active” electron lone pair, and the coordination sphere is hemidirected. The supramolecular features in these complexes are guided and controlled by weak directional intermolecular interactions. The chains interact with each other through π–π stacking interactions creating a 3D framework. The structure of the title complex was optimized by density functional theory calculations. Calculated structural parameters and IR spectra for the title complex are in agreement with the crystal structure. The PbO nanoparticles were obtained by thermolysis of 1 at 180 °C with oleic acid as a surfactant. The average diameter of the nanoparticles was estimated by the Scherrer equation to be 23 nm. The morphology and size of the prepared PbO samples were further observed using SEM.