Number Of Alkoxy Groups Research Articles

Ligand-Induced Intramolecular Redox Diversity in Titanium Complexes with Acenaphthene-1,2-diimine.

A series of the chlorido and alkoxychlorido titanium complexes of the general formula (dpp-Bian)Ti(OiPr)nCl3-n, where dpp-Bian = 1,2-bis[(2,6-iPr2C6H3)imino]acenaphthene n = 0 (2), 1 (3), 2 (4), as well as (dpp-Bian)Ti(OiPr)2 (5) and (dpp-Bian)Ti(OiPr)Cl3 (3-Cl), were isolated and characterized using single-crystal X-ray diffraction analysis and spectroscopic studies combined with density functional theory (DFT) calculations. In the solid state, compounds 2-4 reveal a square-pyramidal geometry at the metal center supported with monoanionic dpp-Bian, whereas 3-Cl with a neutral diimine ligand and 5 bearing a dianionic enebisamide dpp-Bian show, respectively, an octahedral and tetrahedral coordination surrounding the metal ion. Paramagnetic complexes 2-4 exhibit electron paramagnetic resonance spectra in both toluene solution and solid state, confirming the transfer of spin density from the metal ion to the dpp-Bian ligand as the number of alkoxy groups increases. The increase in polarity of the Ti-N bonds in the row 2 < 3 < 4 contributes to enhanced stability of the metal complexes with respect to O-donor molecules. Thus, in tetrahydrofuran (THF), compounds 2 and 3 undergo reversible solvolysis, whereas complex 4 is stable. The charge and spin density distributions as well as molecular orbital energies in 2-4 were analyzed on the basis of DFT calculations which also provided information on the electronic transition energies, absorption band assignments, and thermodynamic parameters of the reactions between the complexes and THF.

Influence of Different Substitution Patterns on the 2D Crystalline Aggregation of Small Molecules on HOPG Surfaces.

A series of benzoic and terephthalic acid derivatives and their corresponding ethyl esters have been synthesized. These are decorated with dendritic units carrying alkoxy chains that differ in the number of alkoxy groups and/or their substitution pattern. These molecules were deposited from solution on highly oriented pyrolytic graphite, and the resulting supramolecular surface patterns have been studied by scanning tunneling microscopy at the solid/liquid interface. Thus, we were able to perform a systematic study on the influence of orthogonal functional groups governing the supramolecular assembly, that is, the alkoxy chains of dendritic units and the carboxylic acid (ester) functions, on the intermolecular interactions, that is, van der Waals interactions and hydrogen bonding between the adsorbed species that drive the pattern formation.

Synthesis and liquid crystalline properties of novel fluorinated N-benzoyl thiourea compounds. Effect of perfluoroalkyl chains on the thermal behavior and smectic phases stability

A series of novel N-benzoyl-N’-aryl thiourea derivatives (BTU) bearing different number of alkoxy groups in terminal positions of benzoyl unit and a perfluorooctyl group on the other side have been designed and prepared. Their liquid crystalline properties were investigated by a combination of three techniques: polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and variable-temperature powder X-ray diffraction (XRD). Their thermal stability was studied by thermogravimetric analysis (TG). It was found that only the compounds which have only one alkoxy chain attached to benzoyl unit, 1a and 1b, show calamitic mesomorphic behavior, with smectic A and C phases being displayed. The type and stability of these mesophases are greatly influenced by the alkyl chain length as well as by the presence of perfluorooctyl group. The clearing and the mesophase ranges are significantly increased with the incorporation of perfluoroalkyl chains when compared to non-fluorinated analogues, with almost 40°C. The attachment of additional alkoxy groups on the benzoyl moiety led to a significant decrease of the clearing points and suppression of the mesogenic character.

Luminescent palladium(II) metallomesogens based on cyclometalated Schiff bases and N-benzoyl thiourea derivatives as co-ligands

Luminescent cyclometalated palladium(II) complexes based on Schiff bases and N-benzoylthiourea (BTU) ligands with different numbers of alkoxy groups at their periphery were designed and prepared. The BTU ligands coordinate through the O and S atoms in a deprotonated bidentate fashion as confirmed by IR and NMR spectroscopy data. Additionally, giving the asymmetrical structure of BTU ligands, the 1H-NMR showed the presence of only one of the two possible isomers. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM) and differential scanning calorimetry (DSC) while their thermal stability was studied by thermogravimetric analysis (TGA). The mesomorphic behavior of palladium(II) complexes depends on the number and chain length of alkoxy groups grafted on BTU derivatives (monotropic smectic A and C phases). The palladium(II) complexes are thermally stable on a broad temperature range up to about 220 °C. Interestingly, when the number of alkoxy groups on the BTU ancillary ligands was increased, the corresponding palladium(II) complexes lost their mesogenicity and only melting to the isotropic state was observed. The solid-state emission spectra of palladium(II) complexes show two maxima around 580 and 650 nm, respectively, with a shoulder around 710 nm when the samples are irradiated in the 330–380 nm range.

Polyethyleneglycol grafting of y-alumina membranes for solvent resistant nanofiltration

A method is presented for grafting mesoporous γ-alumina (pore size 5 nm), supported on an α-alumina ceramic membrane, with polyethylene glycols (PEG). The grafting performance of γ-Al2O3 powders with various PEG grafting agents, having different molecular weights, alkoxy groups, and ureido functionality, was analyzed by TGA, 29Si-NMR, FTIR, and the BET method. FTIR analysis indicated that grafting has occurred. It was found that the molecular weight, the presence of an ureido functionality and the number of hydrolyzable groups of the grafting agents influenced the grafting density. The highest grafting density in this work was obtained by using a silylated ureido PEG with the shortest chain length (n = 10), while the number of alkoxy groups of the grafting agents influenced the structural configuration of the grafted moiety. The grafted membrane surface showed a hydrophilic character. A decrease in solvent permeation of both ethanol and hexane after grafting was observed, due to the presence of the grafted moiety inside the membranes reducing the membrane pore diameter. The permeability with respect to different types of solvents (polar and nonpolar) was investigated. Lower permeability of ethanol than hexane was observed accompanied by a higher retention of Sudan Black in ethanol than in hexane. This effect is explained by the difference in solvent sorption in the grafted moiety for different types of permeating solvents.

New liquid crystals derived from thiophene connected to the 1,2,3-triazole heterocycle

In this work, six new compound derivatives from thiophene were synthesised. The three symmetrical compounds were synthesised containing two heterocyclic 1,2,3-triazole on each side of thiophene, 2,5-disubstituted and the three non-symmetrical compounds were synthesised containing alkyne groups as a spacer in replacing one of these heterocycles. The structural modifications were made by changing the number of alkoxy groups in order to understand the relation between structure and mesomorphic behaviour. Some of the compounds presented liquid crystalline properties, smectic and nematic mesophases. The non-symmetrical compounds allowed for a low emission in the blue region.

Molecular Engineering of Zinc Phthalocyanine Sensitizers for Efficient Dye-Sensitized Solar Cell

Dye-sensitized solar cells (DSSCs) have been expected as low-cost, lightweight, and flexible energy conversion devices. To date, the highest conversion efficiency above 12 % has been achieved with p-conjugated macrocyclic zinc porphyrin sensitizer YD2-o-C8 using cobalt polypyridine redox shuttles. Designed p-conjugated macrocycles such as porphyrins and phthalocyanines have attracted special attention as versatile molecular platforms of highly efficient dyes for DSSCs. While a lot of porphyrin-based sensitizers have been designed and synthesized to enhance the conversion efficiency in DSSCs, the efficiencies of DSSCs employing red/near-IR absorbing phthalocyanine-based sensitizers had not been impressive due to their strong tendency to aggregate and the lack of directionality of electron transfer in the excited states. To overcome these drawbacks of phthalocyanine-based sensitizers, several approaches such as steric suppression of aggregation, electronic push-pull structures through asymmetrical substitutions, and optimization of adsorption sites have been reported. Recently, we showed that the structural modification of peripheral bulky substituents and adsorption site around the phthalocyanine core induced the improvement of incident photon-to-current efficiency (IPCE), and thereby achieved a solar-to-electric power-conversion efficiency (PCE) of 5.9% from solar cells employing PcS18 under one sun condition. However, while the maximum value of IPCE was more than 80 %, the values around 520 nm was about 30 %. Since the absorption coefficient of the sensitizers at the wavelength is very low, in order to increase the efficiency, higher dye adsorption density is desired. This can be done by decreasing the molecular size. In addition to IPCE spectrum, open circuit voltage of the PcS18 cell was not high. This could be improved by modifying the size of peripheral substituents attached to the phthalocyanine core to cover the TiO2 surface by the dye molecules. In this presentation, we examine the effect of the length and number of alkoxy groups around the phthalocyanine moiety on the photovoltaic properties. We now expect the alkoxy groups to have three functions, preventing aggregation, filling the space among dyes on TiO2 surface and increasing dye adsorption density. We found that an asymmetrical zinc phthalocyanine (ZnPc) PcS20 bearing propoxy groups in the 2 and 6 positions of peripheral phenoxy units showed a record PCE value of 6.4 % under simulated air mass 1.5 global sunlight.

Enhancement of smectic C mesophase stability by using branched alkyl chains in the auxiliary ligands of luminescent Pt(II) and Pd(II) complexes

A novel series of Pd(II) and Pt(II) complexes based on cyclometallated imine ligands and N-benzoylthiourea (BTU) derivatives as auxiliary ligands has been prepared and their liquid crystalline properties as well as photophysical properties have been investigated. The crystal structure of one cyclometallated Pt(II) complex with N-(p-F-phenyl)-N′-benzoylthiourea as a co-ligand has been solved. The liquid crystalline properties have been investigated by a combination of DSC, POM and variable temperature powder X-ray diffraction. These new metallomesogens display either a monotropic SmC phase or both SmA and SmC phases, depending on the number of alkoxy groups attached to the imine ligand, alkyl chain length or the use of branched alkoxy terminal groups. We found that the introduction of branched alkoxy terminal groups lead to lower transition temperatures and stabilization of the SmC phase in both the Pd(II) and Pt(II) complexes. While the Pd(II) complexes display no emission, the Pt(II) complexes show good emission properties in solution, in the solid state and as a PMMA film at room temperature, and their investigation is reported.

Hydroxyl Terminated Hydrophilic Silanes

Hydroxyakyl terminated silanes were prepared by reacting 3-aminopropyl alkoxysilanes with ethylene carbonate. Unlike most silanes, these hydrophilic silanes are partially hydrolyzed in water and the siloxane oligomers thus obtained remain soluble in the water. Further condensation leads to water soluble linear or branched polysiloxanes depending on the structure of the hydroxylalkyl terminated silane. The water solubility is not limited to a narrow pH range and does not require alcohols (or other additives). The preparation method of these silanes was found to proceed smoothly at RT with no need for a solvent or a catalyst. The reactions followed second order reaction kinetics irrespective of the number of alkoxy groups attached to the silicon atom. Some condensation was unavoidable even in the absence of any catalyst but the viscosity remained low (0.10–0.16 Pa·sec) and was primarily dependent on the density of branching and the extent of the hydrogen bonding. The structures of these silanes were confirmed by FTIR, 1H NMR and 29Si NMR.

Surface Analysis of Silane Nanolayer on Silica Particles Using 1H Pulse NMR

The surface treatment of spherical silica particles with silane coupling agent having mercapto group was carried out and structure and amount of silane nanolayer formed on silica surface were analyzed using 1H pulse nuclear magnetic resonance (NMR) and thermogravimetric analysis, respectively. Effects of loading amount and number of alkoxy groups of silane on the structure were investigated. Silanes with dialkoxy and trialkoxy structures were used as silane coupling agents and the loading amount of the silane on the silica surface was varied from one to nine times the amount required for monolayer coverage. The relaxation time was longer in the dialkoxy type than in the trialkoxy type of silane. The relaxation time increased with increase of the loading amount of silane for the dialkoxy type; on the other hand, there was no influence of the loading amount of silane for the trialkoxy type. It was found that the silane structure was flexible for the dialkoxy type, whereas it was rigid for the trialkoxy type. Effect of mixing ratio of silane coupling agents having di- and trialkoxy groups on the silane nanolayer structure was also investigated, and 1H pulse NMR studies confirmed that the relaxation time measured for the mixed silane-treated system was between those for the dialkoxy and the trialkoxy structures and depended on the mixing ratio. It was found that the network density of silane-treated layer on silica particles could be controlled by varying the molar ratio of dialkoxy/trialkoxy silane coupling agents.

Oligomeric Alkoxysilanes with Cagelike Hybrids as Cores: Designed Precursors of Nanohybrid Materials

Well-defined alkoxysilane oligomers containing a cagelike carbosiloxane core were synthesized and used as novel building blocks for the formation of siloxane-based hybrid networks. These oligomers were synthesized from the cagelike trimer derived from bis(triethoxysilyl)methane by silylation with mono-, di-, and triethoxychlorosilanes ((EtO)(n)Me(3-n)SiCl, n=1, 2, and 3). Hybrid xerogels were prepared by hydrolysis and polycondensation of these oligomers under acidic conditions. The structures of the products varied depending on the number of alkoxy groups (n). When n=2 and 3, microporous xerogels (BET surface areas of 820 and 510 m(2) g(-1), respectively) were obtained, whereas a nonporous xerogel was obtained when n=1. (29)Si NMR spectroscopic analysis suggested that partial rearrangement of the siloxane networks, which accompanied the cleavage of the Si-O-Si linkages, occurred during the polycondensation processes. By using an amphiphilic triblock copolymer surfactant as a structure-directing agent, hybrid thin films with a 2D hexagonal mesostructure were obtained when n=2 and 3. These results provide important insight into the rational synthesis of molecularly designed hybrid materials by sol-gel chemistry.

Proton-conductive sol–gel membranes from phenylvinylphosphonic acid and organoalkoxysilanes with different functionalities

Novel proton-conductive inorganic–organic hybrid membranes were synthesized from styryl-substituted alkoxysilanes containing different numbers of methoxy groups and phenylvinylphosphonic acid (PhVPA) through the use of radical copolymerization followed by sol–gel process. The substituted alkoxysilanes were copolymerized with phenylvinylphosphonic acid yielding copolymers that were chemically bound with phosphonic acid groups. The mechanical properties and flexibility of these membranes reflected the type of Si–O–Si linkages, which were controlled through the number of alkoxy groups on the Si atoms in the starting organosiloxane compounds. The proton conductivity of the hybrid membranes increased with increasing phosphonic acid content and with decreasing inorganic Si–O cross-linking. The membrane from difunctional methyl (dimethoxy)silylmethylstyrene/PhVPA = 1/4 exhibited a conductivity of 3.4 × 10 −3 S cm −1 under about 19.2% R.H. at 130 °C.

Alkoxysilylated-Derivatives of Double-Four-Ring Silicate as Novel Building Blocks of Silica-Based Materials

Novel oligomeric alkoxysilanes consisting of double-four-ring (D4R) units functionalized with mono-, di-, and trialkoxysilyl groups (designated as 1, 2, and 3, respectively) were designed as nanobuilding blocks for synthesizing silica-based nanomaterials. Hydrolysis and polycondensation of these oligomers were performed under acidic conditions. The gelation occurred much faster than monomeric, dimeric, and cubic octameric alkoxysilanes, which should depend on both molecular size and siloxane structures. Structural analyses of the xerogels derived from 1−3 strongly suggested that the D4R units are at least partly retained in their frameworks. The number of alkoxy groups had a large effect on their porosities: the xerogel derived from 2 was a microporous solid with the BET surface area of 600 m2 g−1, whereas 1- and 3-derived xerogels had very low BET surface areas. Furthermore, mesostructured silica films were successfully synthesized from 2 and 3 by using amphiphilic triblock copolymer surfactant as a stru...

Thio sol–gel synthesis of titanium disulfide thin films and nanoparticles using titanium(IV) alkoxide precursors

Titanium tetraisopropoxide reacts with hydrogen sulfide in butylamine solvent at room temperature to form an amorphous titanium alkoxy-sulfide which can be converted to crystalline titanium disulfide by heat treatment in a flowing hydrogen sulfide gas stream. The reaction has been studied using infrared and Raman spectroscopy, gas chromatography–mass spectrometry, X-ray diffractometry and energy-dispersive X-ray analysis measurements. Based on these studies, it is shown that a partially thiolysed alkoxide precursor forms through the replacement of a limited number of alkoxy groups by hydrosulfide moieties. This alkoxy-hydrosulfide is believed to form following a thiolysis–condensation mechanism similar to the hydrolysis–condensation process that occurs during the corresponding oxide sol–gel reaction. The alkoxy-hydrosulfide species can then be completely thiolysed at 800 °C in a stream of hydrogen sulfide to yield pure, hexagonal titanium disulfide in either film or particulate form.

A Qualitative Examination of the Effects of Silicon Substituents on the Efficiency of Cross-Coupling Reactions

A qualitative study of the effects of various substituents on the silicon atom in cross-coupling reactions of alkenylsilanes has been carried out. In intermolecular competition experiments, the influence of carbon-based groups (methyl, ethyl, isopropyl, tert-butyl, phenyl, and 3,3,3-trifluoropropyl) and alkoxy groups (monoethoxydimethyl-, diethoxymethyl-, and triethoxy) on the silicon have been evaluated under activation by two different methods, fluoride (TBAF) and silanolate (TMSOK). The influence of the substituents was highly dependent on the method of activation. In the presence of TBAF, there was only a modest steric effect (except for tert-butyl substituents), and the efficiency decreased slightly with increasing numbers of alkoxy groups. In the presence of TMSOK, a significant steric effect was noted, but the number of alkoxy groups had almost no influence. These trends were interpreted in terms of the divergent mechanisms for the cross-coupling process.

Polylactones 60: Comparison of the Reactivity of Bu3SnOEt, Bu2Sn(OEt)2, and BuSn(OEt)3 as Initiators of ϵ‐Caprolactone

Bu3SnOEt, Bu2Sn(OEt)2, and BuSn(OEt)3 were used as initiators of ring‐opening polymerizations of ϵ‐caprolactone conducted in 2 M solutions in chlorobenzene with monomer/functional group ratios of 50/1. Time‐conversion curves were recorded in the temperature range of 30–90°C. The reactivity of the initiators increased with the number of alkoxy groups attached to the tin atom. Analogous results were obtained with Bu3SnOMe and Bu2Sn(OMe)2. MALDI‐TOF mass spectra of the polyesters isolated after 98–99% conversion indicated the presence of small amounts of cyclic oligomers (up to 2000 Da) even at reaction temperatures as low as 30°C. Due to transesterification also broad molecular weight distributions were found.

Effect of silane coupling agent adsorbate structure on adhesion performance with a polymeric matrix

The effect of the silane coupling agent adsorbate structure on adhesion performance is investigated. Glass beads are treated with two different sets of silanes where each set contains the same organo-functional group, but a different number of alkoxy groups, viz. one, two, or three. Adhesion strength measurements were obtained from tests in which single, silane-treated glass beads were imbedded into rectangular poly (vinyl butyral) specimens that were then subjected to an applied tensile stress until failure occurred at one of the poles of the sphere. The results indicate that the mono-alkoxy silanes have the least effect on adhesion, the consequence of poor attachment of the silane to the mineral surface, while the di- and tri-alkoxy silanes produce a marked increase in adhesion strength due to the increased stability of their bonds to the glass surface and their ability to form more extensive interphases with the polymer.

コンポジットの界面と接着 ２．界面相（Ｉｎｔｅｒｐｈａｓｅ）形成の効果

The surface treatment of glass beads, chosen as model filler, was carried out using four kinds of silane coupling agents with multilayer coverage. The silanes used have aminopropyl or methacryloxypropyl group, and two or three alkoxy groups. The amount of silane detected on the bead surface was 4-6 times of that required for the monolayer coverage. Using these treated beads, the effects of the organofunctional group and the number of alkoxy groups of silanes on the mechanical properties of the bead-filled poly(vinyl chloride), chosen as typical ductile polymer, were investigated. As a result, the yield stress was improved by the surface treatment, and was higher in the silane having aminopropyl group than in that having the methacryloxypropyl group. The surface treatment with silanes having two alkoxy groups was more effective than those having three alkoxy groups. However, the elongation at break decreased by the surface treatment in the inverse order.

Surface structure of silane-treated glass beads and its influence on the mechanical properties of filled composites

The surface treatment of glass beads, chosen as a model filler, was carried out using four different silane coupling agents with multilayer coverage. For this purpose, silanes having an aminopropyl or a methacryloxypropyl group as an organofunctional group with di- or tri-alkoxy structures were used. The amount of silane detected on the bead surface was four to six times that required for a monolayer coverage. The topography of the silane layer on the bead surface was observed using an atomic force microscope. The topography was strongly affected by the composition of the silane solution and the number of alkoxy groups in the silane. The effects of the organofunctional group and the number of alkoxy groups of the silanes on the mechanical properties of bead-filled poly(vinyl chloride), chosen as a typical ductile polymer, were investigated. A higher yield stress was observed for the silane with an aminopropyl group than for that with a methacryloxypropyl group. Furthermore, for each organofunctional group, the yield stress was higher for the silane with a dialkoxy structure than for that with a trialkoxy structure. However, their effects on the elongation-at-break were contrary to the above tendencies.

ChemInform Abstract: The First Directed Reduction of β-Alkoxy Ketones to anti-1,3-Diol Monoethers: Identification of Spectator and Director Alkoxy Groups.

A new reduction procedure for the stereoselective reduction of certain β-alkoxy ketones is described. The method relies upon electron-transfer reduction using samarium diiodide in THF with MeOH as an additive. Reduction is facile for a number of alkoxy groups that can complex samarium effectively but is not observed with TBS or benzyl protecting groups. Experiments with deuterated methanol show that the stereoselectivity arises from protonation of a samarium carbanion intermediate.