Xinjiao Wang

Long-alkyl-chain-derivatized imidazolium salts and ionic liquid crystals with tailor-made properties

A series of new 1,3-dialkylimidazolium salts with the general formula [CnCnIM][A] (for n = 12; A = PF6−, OTf−, NTf2−; for n = 10, 14, 16, and 18; A = BF4−, ClO4−) has been synthesized. The [C12C12IM][A] salts are ionic liquids at room temperature, whereas all [CnCnIM][BF4] and [CnCnIM][ClO4] (n = 10, 14, 16, 18) salts demonstrate a liquid crystalline phase at elevated temperatures that have a large mesophase window, which varies from 10 to 80 °C with increasing alkyl chain length. In particular, [C10C10IM][BF4] shows liquid crystalline behavior at room temperature and therefore is potentially suitable for application as a pre-organized reaction medium in synthesis and catalysis. Viscosity studies of [C16C16IM][BF4] and the corresponding perchlorate salt demonstrate strong non-Newtonian viscosity behavior for the liquid crystalline state of these ionic liquids.

Ethylene to 2-Butene in a Continuous Gas Phase Reaction using SILP-Type Cationic Nickel Catalysts

Owing to shifting market demands, it is important to convert ethylene to propylene. One attractive way to achieve this conversion is the dimerization of ethylene to 1‐butene, followed by isomerization to 2‐butene and subsequent metathesis of 2‐butene/ethylene olefin. Our contribution focuses on combining the first two steps. Herein, we report a highly selective tandem dimerization/isomerization of ethylene to 2‐butene catalyzed by homogeneously dissolved cationic nickel complexes. These catalysts can be efficiently immobilized by using the supported ionic liquid phase technology. Such supported ionic liquid phase materials have been tested under continuous gas phase conditions and demonstrated attractive catalytic performance with respect to both catalyst stability and productivity after the optimization of support, ionic liquid, ligand, and process parameters. The limited thermal stability of the nickel complexes and olefin condensation at too low temperatures require a careful thermal management of the fixed‐bed reactor.

Ordering and Phase Transitions in Ionic Liquid‐Crystalline Films

Ionic liquids are low melting salts that combine extremely low vapor pressures with a large number of interesting chemical and physicochemical properties depending on the nature of their cation/anion combination. Apart from bulk ionic-liquid applications, a concept known as “supported ionic liquid phase (SILP)” technology has attracted a lot of attention in the recent five years. In SILP materials, a very thin film of ionic liquid (typically a couple of nanometers thick) is confined on the surface of a solid by physisorption, tethering, or covalent anchoring of ionic liquid fragments. In this way, a material is obtained, the surface of which is modified by a molecular defined liquid with extremely low vapor pressure. Surface properties that can be realized in this manner depend on the chemical nature of the ionic liquid (e.g. acidic or complexing properties) or on the functionalities of compounds (e.g. catalyst complexes or molecular carriers) dissolved therein. The concept is actually investigated in detail for the design of new catalytic materials, new adsorber systems or new supported liquid membranes. Ionic liquid crystals (ILCs) are formed by one or two anisotropically shaped ions involving, typically, imidazolium ions with long N-alkyl substituents (i.e. , CnH2n + 1 alkyl substituents with n 12). Compared to “traditional”, neutral liquid crystals, ILCs offer the additional feature of displaying ionic conductivity. In addition, they form uncommon ordering of their liquid-crystalline states due to strong coulombic and van der Waals interactions. Interestingly, their ability to form smectic mesophases in easily accessible temperature ranges (in most cases below 100 8C) leads to temperature-switchable structures and properties. Confining ILCs on solids in a SILP-type fashion is a highly interesting, yet fully unexplored, concept to obtain new SILP materials with attractive thermomorphic surface properties. SILP catalysis in a temperature-switchable anisotropic environment or temperature-switchable selectivities of ILC-SILP membranes are only two fascinating potential applications of such new materials. Herein, we provide for the first time spectroscopic insights into the behavior of ILC films physisorbed in a SILP-type fashion on a planar support. By describing in detail the structural changes induced in supported ILCs by temperature variation we create a fundamental basis to explore these options in great detail in the near future. In spite of the intriguing idea to use supported LC thin films as temperature-switchable functional surfaces for, for example, catalysis or separation technologies, experimental verification of the concept turns out to be demanding. The reason is that there are hardly any experimental probes which would allow us to monitor the local structure and ordering of LC thin films when dispersed on porous catalyst supports. Typical methods such as polarized optical microscopy (POM) or differential scanning calorimetry (DSC) are not applicable, at least in the limit of low loadings. However, direct information on the structure of the ILC phase is crucial, as both the dissolved catalyst and the reactants may have an appreciable influence on the structure of the LC phase. Thus, the degree of ordering in the LC phase under reaction conditions may substantially differ from the pure ILC phase. Also, the support may impose structural effects on the LC phase. Interactions with the support surface or the confinement in small nanometer-sized pores may shift or suppress phase transitions. It will not be possible to monitor such phenomena with conventional methods such as DSC or POM. Here, the application of vibrational spectroscopy may be helpful to provide the desired information. Fourier-transform infrared (FTIR) spectroscopy has been used as a tool to monitor the local structure in organic thin-film systems including Langmuir–Blodgett (LB) films and self-assembled monolayers (SAM) . From band intensities and positions of the CH2 antisymmetric stretching, symmetric stretching, scissoring, and rocking modes, information can be extracted on the molecular orientation, the degree of ordering, the concentration of gauche defects and even on the subcell packing (see e.g. ref. [32] and references therein for details). FTIR spectroscopy can be straightforwardly applied both to powders using diffuse reflectance IR FT spectroscopy (DRIFTS) and to planar surfaces using IR reflection absorption spectroscopy (IRAS), the latter with submonolayer sensitivity. Although IRAS has been extensively used to investigate molecular orientation at interfaces, to the best [a] M. Sobota, M. Happel, Dr. M. Laurin, Prof. Dr. J. Libuda Lehrstuhl f r Physikalische Chemie II Friedrich-Alexander-Universit t Erlangen-N rnberg Egerlandstrasse 3, 91058 Erlangen (Germany) Fax: (+ 49) 9131-8528867 E-mail : mathias.laurin@chemie.uni-erlangen.de libuda@chemie.uni-erlangen.de [b] Prof. Dr. K. Meyer, Prof. Dr. P. Wasserscheid, Prof. Dr. J. Libuda Erlangen Catalysis Resource Center Friedrich-Alexander-Universit t Erlangen-N rnberg Egerlandstrasse 3, 91058 Erlangen (Germany) [c] X. Wang, Prof. Dr. K. Meyer Lehrstuhl f r Anorganische Chemie Friedrich-Alexander-Universit t Erlangen-N rnberg Egerlandstrasse 1, 91058 Erlangen (Germany) [d] Dr. M. Fekete, Prof. Dr. P. Wasserscheid Lehrstuhl f r Chemische Reaktionstechnik Friedrich-Alexander-Universit t Erlangen-N rnberg Egerlandstrasse 3, 91058 Erlangen (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201000144.

Functional nickel complexes of N-heterocyclic carbene ligands in pre-organized and supported thin film materials

Nickel(II) complexes with double alkyl chain functionalized N-heterocyclic carbene (NHC) ligands, [NiCl2(C12MIM)2] and [NiCl2(C12C12IM)2], where C12MIM = 1-dodecyl-3-methylimidazolin-2-ylidene (1) and C12C12IM = 1,3-didodecylimidazolin-2-ylidene (2), have been prepared and fully characterized by 1H NMR, 13C NMR, and CHN elemental analyses. Furthermore, we have developed a system, in which double long alkyl chain derivatized Ni–NHC complexes are dissolved in the related ionic liquid crystalline 1,3-didodecylimidazolium tetrafluoroborate, [C12C12IM][BF4], to form pre-organized structures for enhanced reactivity. Remarkably, differential scanning calorimetry, polarized optical microscopy, and temperature-programmed IR reflection absorption spectroscopy performed on a mixture of 10 wt% Ni complexes in [C12C12IM][BF4] demonstrate that this system retains an ionic liquid crystalline phase; even after immobilization onto a silica-100 support with pore filling α = 1.

Highly Luminescent Salts Containing Well-Shielded Lanthanide-Centered Complex Anions and Bulky Imidazolium Countercations

Four salts containing imidazolium cations and europium(III)- or terbium(III)-centered complex anions have been successfully synthesized from an ethanol/H2O solution. The single-crystal X-ray diffraction analyses reveal that these compounds have a common formula of [R][Ln(DETCAP)4] [R = 1-ethyl-3-methylimidazolium (C2mim), Ln = Eu (1) and Tb (2); R = 1-butyl-3-methylimidazolium (C4mim), Ln = Eu (3) and Tb (4); DETCAP = diethyl-2,2,2-trichloroacetylphosphoramidate], in which the lanthanide centers are chelated by four chelating pseudo-β-diketonate ligands (DETCAP)(-), forming the respective complex anions. Their thermal behaviors and stabilities were also investigated to study the role of the length of the side chain in the cations. Fluorescence measurements at both room temperature and liquid-nitrogen temperature show that these materials show intense characteristic europium(III) or terbium(III) emissions and have long decay times. Their overall quantum yields were determined to be in the range of 30-49%.

Dimerization of ethene in a fluidized bed reactor using Ni-based Supported Ionic Liquid Phase (SILP) catalysts

The complexes [(mall)Ni(dppanis)][SbF6] (mall = methallyl, dppanis = (2-methoxyphenyl)diphenylphosphine) 1, [(mall)Ni(PPh3OC10)][SbF6] (PPh3OC10 = (2-decyloxyphenyl)diphenylphosphine) 2, and [(mall)Ni(PPh3OdiMePh)][SbF6] (PPh3OdiMePh = (2-(2,6-dimethylphenoxy)phenyl)diphenylphosphine) 3 were immobilized as Supported Ionic Liquid Phase (SILP) catalysts and applied for the tandem dimerization/isomerization of ethylene to 2-butene in a fluidized bed reactor. The better heat removal in the fluidized bed improves the catalyst stability and allows for a more detailed investigation of the deactivation mechanism. Based on kinetic studies, a second order deactivation mechanism is proposed, in which two nickel complexes dimerize if the supply of ethene is insufficient.

Implementation of a digital amplitude detector based on the Cordic transform

A digital implementation of an amplitude detector for Automatic Gain Control in a complex modulation format receiver is presented. The algorithm is based on the Co-Ordinate Rotation Digital Computer method which makes the amplitude detection very fast and accurate. The efficient topology enables realisation in a standard programmable gate array. Measurements on a 16QAM burst mode receiver are presented.

16 QAM burst mode receiver for upstream communication over CATV networks

This paper discusses a 16 QAM burst mode receiver system for upstream communication over the CATV network. A prototype is realised in a hybrid analog-digital technology using standard programmable logic components. Efficient data transport is ensured by partially overlapping phase, amplitude and symbol timing recovery during a preamble with fixed content. Important technical issues and measurements are presented.