bluuebunny/crossref_metadata_2025 huggingface dataset:
Red‐Emitting Fluorenes as Efficient Emitting Hosts for Non‐Doped, Organic Red‐Light‐Emitting Diodes
Authors: Chiang C.‐L. , Wu M.‐F. , Dai D.‐C. , Wen Y.‐S. , Wang J.‐K. , Chen C.‐T.
Published: February 2005

Rare red‐fluorescent fluorene derivatives have been designed and synthesized. The long‐wavelength red fluorescence is achieved by incorporating a di(4‐tolyl)amino or diphenylamino electron donor and a dicyanovinyl electron acceptor. The single‐crystal X‐ray structures of the di(4‐tolyl)amino (pTSPDCV) and diphenylamino (PhSPDCV) compounds indicate only weak non‐π van der Waals contacts in addition to long‐distance dipole–dipole interactions of the red‐emitting fluorene molecules in the solid state. The aggregation of the dipolar fluorene is largely suppressed by introducing bulky 9,9‐substituents (spiro‐fused bifluorene) as well as a non‐planar di(4‐tolyl)amino or diphenylamino group. In the solid state, these fluorene derivatives all show red fluorescence that is much brighter than with the red dopants Nile Red and DCM (4‐(dicyanomethylene)‐2‐methyl‐6‐[4‐(dimethylaminostyryl)‐4H‐pyran]). The unique photophysical properties of red‐emitting fluorene derivatives differ from other known red dopants and facilitate the fabrication of non‐doped red organic light‐emitting diodes (OLEDs). Authentic red (CIE, x = 0.65, y = 0.35) electroluminescence with a brightness of more than 12 000 cd m–2 (greater than 600 cd m–2 at 20 mA cm–2) and a remarkable external quantum efficiency as high as 3.6 % have been observed for the red‐emitting OLEDs with pTSPDCV or PhSPDCV as the sole emitting host.
Synthesis and Assembly of Gold Nanoparticles in Quasi‐Linear Lysine–Keggin‐Ion Colloidal Particles
Authors: Sanyal A. , Mandal S. , Sastry M.
Published: February 2005

The formation of fiber‐like colloidal particles of the amino acid lysine complexed with Keggin ions is demonstrated. The lysine–phosphotungstic acid (PTA) colloidal particles act as excellent templates for the synthesis and assembly of gold nanoparticles wherein the lysine‐PTA complex acts as a UV‐switchable reducing agent for gold ions. This novel bio‐organic–inorganic template shows excellent potential as a regulated nanoreactor for application in programmed nanoparticle synthesis and assembly in a single step.
Novel Europium‐Complex/Nitrile‐ Butadiene Rubber Composites
Authors: Liu L. , Lu Y.‐L. , He L. , Zhang W. , Yang C. , Liu Y.‐D. , Zhang L.‐Q. , Jin R.‐G.
Published: February 2005

The novel europium complex acrylato(1,10‐phenanthroline)bis(2‐thenoyltrifluoroacetonato)europium(III) [Eu(tta)2(aa)(phen)] [Eu‐AAPhen; Htta = 4,4,4‐trifluoro‐1‐(2‐thienyl)‐1,3‐butanedione, Haa = acrylic acid, phen = 1,10‐phenanthroline], which combines the excellent fluorescence properties of [Eu(tta)3(phen)] and the reactivity of acrylic acid with radicals, has been synthesized. Various amounts of this complex (powder) are mixed with nitrile‐butadiene rubber (NBR) and peroxide to form uncured composites. These composites are vulcanized to obtain cured Eu‐AAPhen/NBR composites. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that the dispersion dimension for the cured composites is far finer than that for the uncured composites. Wide‐angle X‐ray diffraction (WAXD) experiments show that the crystallinity of Eu‐AAPhen in the composite decreases dramatically after the crosslinking process, implying that in‐situ reactions (including polymerization and grafting) of Eu‐AAPhen initiated by peroxide radicals should take place during the crosslinking of the NBR matrix with peroxide. The dispersion phase of the cured Eu‐AAPhen/NBR composite should be composed of nearly nanometer‐sized aggregates of poly(Eu‐AAPhen) and residual Eu‐AAPhen particles with reduced dimensions. The fluorescence properties of the cured composite are much better than those of the uncured one.
Phospholipid‐Based Catalytic Nanocapsules
Authors: Lawson G. E. , Lee Y. , Raushel F. M. , Singh A.
Published: February 2005

The encapsulation and catalytic efficiency of organophosphate hydrolyzing enzymes in polymer‐stabilized nanocapsules is reported. Polymerized vesicles—derived from a headgroup‐polymerizable phospholipid, 1,2‐dipalmitoyl‐sn‐glycero‐3‐phospho‐N‐(2‐hydroxymethyl)‐3,5‐divinylbenzamide (DPPE‐DVBA)—containing enzymes were used as catalytic nanocapsules. Three enzymes, organophosphorus hydrolase (OPH), phosphotriesterase (PTE), and organophosphorus acid anhydrolase (OPAA), were encapsulated in vesicles by incubating them with freeze‐dried vesicles at 55  °C, followed by intermittent vortex‐mixing. Enzyme‐containing vesicles, collected after gel‐filtration, were stabilized by photopolymerization at 254 nm to yield crosslinked catalytic nanocapsules. The nanocapsules containing OPH and PTE showed specific activities of 0.36 and 1.74 μmol mg–1 min–1, respectively, against methyl parathion (MPT), and OPAA‐containing nanocapsules showed a specific activity of 57.1 μmol mg–1 min–1 against diisopropylfluorophosphate. Freeze‐dried, OPH‐ and PTE‐containing nanocapsules showed retentions of 83 % and 85 % specific activity, respectively, upon redispersion in buffer solution. Three‐week, room‐temperature storage of OPH‐containing nanocapsules showed a retention of 18 % enzyme activity. Hydrolysis of MPT in crosslinked DPPE‐DVBA/OPH vesicles showed that hydrophobic MPT permeated through the bilayer membrane of the freeze‐dried nanocapsules, releasing the hydrolysis product para‐nitrophenol, which permeated back to the exogenous dispersion medium leaving the enzymes free to react with freshly permeated MPT in the interior of the nanocapsules.
Hydrophilic and Antimicrobial Zeolite Coatings for Gravity‐Independent Water Separation
Authors: McDonnell A. M. P. , Beving D. , Wang A. , Chen W. , Yan Y.
Published: February 2005

Condensing heat exchangers onboard manned spacecraft require hydrophilic fin surfaces to facilitate wetting and wicking of condensate to achieve gravity‐independent water separation in the zero‐ or micro‐gravity environment of space. In order to prevent the proliferation of microbes, the coating must also be biocidal. Here we show for the first time that zeolite A and ZSM‐5 coatings deposited via in‐situ crystallization on stainless steel and aluminum alloys have excellent hydrophilicity, biocidal properties, and adhesion. Water contact angles below 5° were obtained on most substrates tested. When silver‐ion exchange is carried out on the zeolite A coating, it becomes highly antibacterial. This biocidal capability of zeolite A is regenerative by repeated ion exchange. All coatings exhibit the highest rating of 5B as determined by adhesion test ASTM D‐3359‐02 (American Society for Testing and Materials). These properties, in addition to zeolite coating's low‐temperature crystallization process and demonstrated corrosion resistance, make zeolite coatings advantageous over the current sol–gel coatings and well suited for use in condensing heat exchangers onboard manned spacecraft.
Acrylate‐Based Photopolymer for Two‐Photon Microfabrication and Photonic Applications
Authors: Nguyen L. H. , Straub M. , Gu M.
Published: February 2005

This paper provides a photopolymerizing material suitable for stereolithography of complex submicrometer‐sized three‐dimensional (3D) structural elements to a broad scientific public. Here, we present the formulation of a polymer (LN1 resin) that allows further research in the field of nanofabrication and ‐technology as it surpasses current material limitations. The polymer consists of multifunctional acrylate oligomers as binder, polyfunctional monomers, and a photoinitiator (PI). The chemistry to form 3D structures is based on photopolymerization of the acrylate system initiated by free‐radical species that are triggered by two‐photon absorption of a PI. Important parameters of photocuring, such as the effects of PI concentration, temperature, and light intensity, were studied using photocalorimetry. The thermal stability of the material was tested using thermal gravimetric analysis, providing key information for electronic and photonic applications. Photonic‐crystal structures generated from this resin exhibiting photonic stop gaps in near‐infrared‐ and telecommunication‐wavelength regions are presented.
Electrophosphorescent Devices Based on Cationic Complexes: Control of Switch‐on Voltage and Efficiency Through Modification of Charge Injection and Charge Transport
Authors: Plummer E. A. , van Dijken A. , Hofstraat J. W. , De Cola L. , Brunner K.
Published: February 2005

This paper reports an analysis of the properties of polymer light‐emitting devices (PLEDs) doped with iridium complexes. Devices based on charged and neutral complexes doped into poly(vinylcarbazole) (PVK) are presented, and the role of the ions and the charge‐transport properties of the complexes are discussed. In devices with the charged complexes, the concentration of the complex is found to have a profound effect on both the switch‐on voltage and the efficiency. At higher doping concentrations the efficiency is increased and the switch‐on voltage decreased. The increase in efficiency and decrease in switch‐on voltage at higher dopant concentration are found to be due to an alternative charge transport path via the iridium dopant [Ir(bpy)]+ (bis(2‐phenylpyridine‐C2,N′)(2,2′‐bipyridine)iridium hexafluorophosphate). However, at lower concentrations the complex becomes an electron trap and the efficiency is reduced. The devices are found to be significantly less efficient than those with neutral complexes. This difference is attributed to the ionic content and the charge trapping properties of the charged complexes. The low efficiency of the charged‐complex‐based devices could be overcome by utilizing a hole‐blocking layer; devices with efficiencies as high as 23 cd A–1 were obtained.
Titania and Mixed Titania/Aluminum, Gallium, or Indium Oxide Spheres: Sol–Gel/Template Synthesis and Photocatalytic Properties
Authors: Deshpande A. S. , Shchukin D. G. , Ustinovich E. , Antonietti M. , Caruso R. A.
Published: February 2005

Porous polymer beads have been used as templates in which sol–gel chemistry was conducted for the formation of porous titanium dioxide and titania/aluminum, gallium, or indium oxide spheres. The addition of 5, 10, and 15 wt.‐% of the second metal oxide to titania was studied, resulting in little variation in the final porous‐sphere diameter, but in a decreased titania nanocrystal size and an increased specific surface area of the material. The crystallinity of the samples was observed after heating at 550, 750, and 950 °C as anatase to rutile phase transitions became apparent and peaks from the added metal oxide were observed with the increase in temperature. Photocatalytic decomposition of 2‐chlorophenol was monitored in the presence of the titania and titania/metal‐oxide spheres showing that a 5 wt.‐% addition of the second metal oxide gave best photocatalytic results for all the metal oxides studied. At a pH of 6 the pure titania spheres were less photocatalytically active than the Degussa P25 titania, however the mixed titania/5 wt.‐% metal‐oxide samples were more active than the standard in the order In (least active), Ga, then Al (most active). Variation of the solution pH (between pH 2 and 10) had little influence on the photocatalytic activity of the titania/5 wt.‐% aluminum oxide material, more effect on the titanium/5 wt. % gallium oxide, and the most pronounced effect on the titanium/5 wt.‐% indium oxide, with increased activity at higher pH values. The adsorption of pyridine to the titania samples containing the second metal oxide indicated the presence of Lewis‐acid sites.
Biomimetic Pattern Transfer
Authors: Wu L.‐Q. , Ghodssi R. , Elabd Y. A. , Payne G. F.
Published: February 2005

Biological systems routinely use phenols to construct complex materials with diverse functions. Typically, these phenolic materials are generated using oxidative enzymes to initiate a cascade of uncatalyzed reactions. We mimic these processes to micropattern films of the aminopolysaccharide chitosan. Specifically, we microfabricate silicon wafers to have gold patterns, cast a chitosan film onto the patterned wafers, and commence pattern transfer by polarizing the underlying gold surfaces to electrochemically initiate the phenol reaction cascade. The electrochemically initiated reactions lead to modification of the chitosan film's chemistry, structure, and fluorescence. Further, electrochemically initiated modification of the chitosan film is localized to the interfacial region between the film and the anode, with resolution in the lateral direction of at least 20 μm. These results demonstrate that electrochemical pattern transfer provides a promising new method for micropatterning flexible films.
Enhanced Electro‐Optic Behavior for Shaped Polymer Cholesteric Liquid‐Crystal Flakes Made Using Soft Lithography
Authors: Trajkovska‐Petkoska A. , Varshneya R. , Kosc T. Z. , Marshall K. L. , Jacobs S. D.
Published: February 2005

Polymer cholesteric liquid‐crystal (PCLC) flakes were investigated for their electro‐optical behavior under an applied alternating‐current field. Shaped flakes, fabricated using soft lithography and suspended in dielectric‐fluid‐filled cells, reoriented more uniformly than randomly shaped flakes made by fracturing of PCLC films. Extensive characterization found shaped flakes to be smooth and uniform in size, shape, and thickness. Reorientation in applied fields as low as tens of mVrms μm–1 was fastest for flakes with lateral aspect ratios greater than 1:1, confirming theoretical predictions based on Maxwell–Wagner polarization. Brilliant reflective colors and inherent polarization make shaped PCLC flakes of interest for particle displays.
Cover Picture: Enhanced Electro‐Optic Behavior for Shaped Polymer Cholesteric Liquid‐Crystal Flakes Made Using Soft Lithography (Adv. Funct. Mater. 2/2005)
Authors: Trajkovska‐Petkoska A. , Varshneya R. , Kosc T. Z. , Marshall K. L. , Jacobs S. D.
Published: February 2005

The cover shows a variety of shaped flakes fabricated from polymer cholesteric liquid‐crystal material using soft lithography. In work reported by Jacobs and co‐workers on p. 217, the micrometer‐sized flakes exhibit brilliant circularly polarized selective reflection colors without polarizers or color filters when placed in a fluid‐filled electro‐optic cell. With the application of a low‐magnitude alternating current field, the flakes reorient in hundreds of milliseconds and the colors disappear.

Polymer cholesteric liquid‐crystal (PCLC) flakes were investigated for their electro‐optical behavior under an applied alternating‐current field. Shaped flakes, fabricated using soft lithography and suspended in dielectric‐fluid‐filled cells, reoriented more uniformly than randomly shaped flakes made by fracturing of PCLC films. Extensive characterization found shaped flakes to be smooth and uniform in size, shape, and thickness. Reorientation in applied fields as low as tens of mVrms μm–1 was fastest for flakes with lateral aspect ratios greater than 1:1, confirming theoretical predictions based on Maxwell–Wagner polarization. Brilliant reflective colors and inherent polarization make shaped PCLC flakes of interest for particle displays.
On the Stereochemical Course of Self‐Replication in Secondary Cycle Sharpless Aminohydroxylation
Authors: Muñiz Kilian
Published: February 2005

An investigation on a potential asymmetric self‐replication process within the secondary cycle of Sharpless asymmetric aminohydroxylation is discussed. The reaction of two model olefins is investigated within this process and two different models for an asymmetric process are discussed. Analysis of the results on the basis of these models and a mathematical description for development of the enantiomeric excesses as a function of olefin conversion lead to the conclusion that for such processes there is no possibility for any inhibitory effect and that asymmetric self‐replication in secondary cycle aminohydroxylation reactions is not a feasible process.
Mononuclear Ruthenium Catalysts for the Direct Propargylation of Heterocycles with Propargyl Alcohols
Authors: Bustelo Emilio , Dixneuf Pierre H.
Published: February 2005

A new family of mononuclear ruthenium catalysts for the catalytic direct propargylation by propargylic alcohols of heterocycles is presented. The catalyst activity can be improved by tuning the ligand's influence and electronic properties at the metal centre. Whereas [(p‐cymene)RuCl(PR3)][OTf] (PR3=PCy3, PPh3) complexes catalyse the propargylation of furan or 2‐methylfuran by the alkynol HC≡CCH(OH)Ph in moderate yield, mononuclear [(p‐cymene)RuCl(CO)(PR3)][OTf] complexes are more active to achieve the same reaction. Low temperature NMR experiments performed on the stoichiometric reaction of the parent [(p‐cymene)RuCl(PR3)][B(ArF)4] and the alkynol show the unexpected in situ formation, via allenylidene and hydroxycarbene intermediates, of the carbonyl complexes [(p‐cymene)RuCl(CO)(PR3)][B(ArF)4] [ArF=3,5‐(CF3)2C6H3] that appear to be the best catalyst precursors.
A Practical and Chemoselective Reduction of Nitroarenes to Anilines Using Activated Iron
Authors: Liu Yugang , Lu Yansong , Prashad Mahavir , Repič Oljan , Blacklock Thomas J.
Published: February 2005

Reduction of nitroarenes to anilines using activated iron generated by Fe/HCl or Zn/FeSO4 is described. A variety of functional groups such as alkyne, ketone, enone, nitrile, lactone, and aromatic halide are well tolerated under these conditions.
Silica Gel Confined Ionic Liquid+Metal Complexes for Oxygen‐Free Carbonylation of Amines and Nitrobenzene to Ureas
Authors: Shi Feng , Zhang Qinghua , Gu Yanlong , Deng Youquan
Published: February 2005

A new kind of silica gel confined ionic liquid containing a metal complex as heterogenized catalysts was prepared for the carbonylation of amines and nitrobenzene without molecular oxygen to afford the corresponding ureas with greatly enhanced catalytic activity (TOF exceeded 11000 mol⋅mol−1⋅h−1), with a much lower amount of ionic liquids being needed, with easy catalyst separation and possible reusability, and avoidance of the using of explosive CO+O2gas mixtures. Such an enhancement in catalytic activity may be derived from the effect of a high concentration of ionic liquid containing a metal complex due to the confinement into the nano‐pores or cavities of the silica gel matrix.
Metallodendritic Catalysis for Redox and CarbonCarbon Bond Formation Reactions: A Step towards Green Chemistry.
Authors: Astruc Didier , Heuzé Karine , Gatard Sylvain , Méry Denise , Nlate Sylvain , Plault Lauriane
Published: February 2005

Metallodendritic catalysts combine the advantages of homogeneous and heterogeneous catalysts: they are soluble and perfectly well defined on the molecular level, and yet they can be recovered by precipitation, ultra‐filtration or ultra‐centrifugation (as biomolecules) and recycled several times. In this article, we summarize our recent work in this field with examples operating under ambient conditions in metathesis, Pd‐catalyzed Sonogashira coupling, redox catalysis of nitrate and nitrite cathodic reduction to ammonia and various oxidation reactions by H2O2 catalyzed by polyoxometallates. The dendritic effects on the catalytic efficiencies are scrutinized, i.e., the comparison of the metallodentritic catalysts with their monomeric models and among the dendrimer generations. It is concluded that metallostars or low‐generation metallodendrimers usually are optimized catalysts in terms of efficiency and recovery/re‐use.
Trimethylphosphine‐bis(benzyl)nickel: Synthesis and Characterization
Authors: Wasilke Julia‐Christina , Ziller Joseph W. , Bazan Guillermo C.
Published: February 2005

The reaction of NiCl2(PMe3)2 with 2 equivs. of benzylmagnesium chloride in THF at −120 °C affords Ni(η1‐CH2C6H5)(η3‐CH2C6H5)PMe3. The formation of this thermally unstable compound is accompanied by bisbenzyl and Ni(0) side products. Single crystal X‐ray analysis confirms the presence of the η1‐benzyl and η3‐benzyl ligands. Reaction of Ni(η1‐CH2C6H5)(η3‐CH2C6H5)PMe3 with 2‐(diphenylphosphino)benzoic acid and activation with B(C6F5)3 gave the expected product [2‐(diphenylphosphino)benzoate tris(pentafluorophenyl)borate‐κ2P,O](η3‐benzyl)nickel.
Iridium‐Catalyzed Enantioselective Hydrogenation of Terminal Alkenes
Authors: McIntyre Steven , Hörmann Esther , Menges Frederik , Smidt Sebastian P. , Pfaltz Andreas
Published: February 2005

Iridium complexes derived from chiral P,N ligands are efficient catalysts for the enantioselective hydrogenation of 2‐aryl‐substituted terminal alkenes. Using 0.1–1 mol % of catalyst at room temperature and ambient hydrogen pressure, high enantioselectivities (88–94% ee), full conversions after short reaction times and essentially quantitative yields were obtained for a range of differently substituted 2‐arylalkenes. Among six iridium complexes that were tested, the most selective catalyst was a complex with a phosphinite‐oxazoline ligand derived from threonine (Ir‐ThrePHOX). In contrast to the hydrogenation of trisubstituted alkenes, a strong pressure effect was observed for this class of substrates. Lowering the hydrogen pressure from 50 to 1 bar resulted in a strong increase of the ee values.
Favored CH Activation in Comparison to Cyclopropyl CC Activation using a Vaska‐Analogous Complex
Authors: Ruhland Klaus , Herdtweck Eberhardt
Published: February 2005

Through ligand exchange reaction of Vaska's complex with a chelating diphosphinite ligand containing a cyclopropyl group, CH activation rather than CC activation of the strained cyclopropyl ring is induced. The activation takes place as a second step preceded by the ligand exchange reaction. The fixation of the CH bond near to the metal through the geometry of the diphosphinite ligand is essential for the activation process.
Oxygen‐Transfer Reactions of Molybdenum‐ and Tungstendioxo Complexes Containing η2‐Pyrazolate Ligands
Authors: Most Kerstin , Hoßbach Jens , Vidović Denis , Magull Jörg , Mösch‐Zanetti Nadia C.
Published: February 2005

Dioxomolybdenum and ‐tungsten compounds containing sterically demanding pyrazolate ligands have been synthesised by treatment of dioxometal halides with the potassium salts of 3,5‐di‐ tert‐butylpyrazole (t‐Bu2pzH) and 3,5‐di‐tert‐butyl‐ 4‐bromopyrazole (t‐Bu2‐4‐BrpzH). The products [MoO2Cl(η2‐t‐Bu2pz)] (1), [MoO2(η2‐t‐Bu2pz)2] (2), [MoO2(η2‐t‐Bu2‐4‐Brpz)2] (3), [WO2(η2‐t‐Bu2pz)2] (4) and [WO2(η2‐t‐Bu2‐4‐Brpz)2] (5) were characterised by spectroscopic techniques. The X‐ray structure of complex 3 reveals a distorted trigonal prismatic geometry with two η2‐co‐ordinated pyrazolate ligands. These high‐valent compounds participate in oxygen‐transfer reactions and catalyse the oxidation of PPh3 with dimethyl sulphoxide. UV/VIS measurements of the oxo‐transfer reactions and the kinetics of the catalytic process are described. By the reaction of 2 with three equivalents of PEt3 or treatment of [MoOCl2(PMe3)2] with two equivalents of t‐Bu2pzK mononuclear mono‐oxo compounds of the type [MoO(t‐Bu2pz)2(PR3)2] (R=Et 6, R=Me 7) were obtained and characterised by X‐ray diffraction analyses. This points to biologically relevant mononuclear Mo(IV) intermediates in the catalytic process with this type of complex.
Evaluation of (η5‐C5Me5)Hf(R)2[N(Et)C(Me)N(t‐Bu)] (R=Me and i‐Bu) for the Stereospecific Living and Degenerative Transfer Living Ziegler–Natta Polymerization of α‐Olefins
Authors: Kissounko Denis A. , Zhang Yonghui , Harney Matthew B. , Sita Lawrence R.
Published: February 2005

The dialkyl(monocyclopentadienyl)hafnium acetamidinates, Cp*Hf(R)2[N(Et)C(Me)N(t‐Bu)] [Cp*=η5‐C5Me5, R=Me (3a) and i‐Bu (3b)], were prepared through either ‘one–pot’ carbodiimide insertion or two‐step salt elimination protocols starting with commercially available Cp*HfCl3. Protonolysis of 3a and 3b with [PhNHMe2][B(C6F5)4] in chlorobenzene produced the cationic complexes, {[Cp*Hf(R)[N(Et)C(Me)N(t‐Bu)]}[B(C6F5)4] [R=Me (4a) and i‐Bu (4b)], which were characterized in solution. Compounds 4a and 4b were evaluated as initiators for the stereospecific living Ziegler–Natta polymerization of 1‐hexene. These results reveal that, while an extremely high level of stereoselectivity can be achieved to produce isotactic poly(1‐hexene) in a living fashion, the rate constant for polymerization, kp, using either 4a or 4b, is ~60 times less than that of the analogous zirconium initiators. Finally, upon substoichiometric activation of 3a with [PhNHMe2][B(C6F5)4] in a 2 : 1 ratio, degenerative transfer living Ziegler–Natta polymerization of 1‐hexene can be accomplished to produce atactic poly(1‐hexene).
Transition Metal Imido Compounds as Ziegler–Natta Olefin Polymerisation Catalysts
Authors: Bolton Paul D. , Mountford Philip
Published: February 2005

Transition metal imido compounds having the general formula [(L)nM(NR)] [where (L)n is a supporting ligand or ligand set, and R typically is alkyl or aryl] have been known for nearly 50 years, and during the last two decades have been the focus of considerable attention. Relatively recently their potential application in the Ziegler–Natta polymerisation of olefins has been realised. In this contribution we review the Ziegler–Natta polymerisation of olefins by transition metal imido compounds. A general introduction to homogeneous Ziegler–Natta olefin polymerisation and key aspects of transition metal imido chemistry is given, followed by a short description of a related imido‐based polymerisation process, namely ring‐opening olefin metathesis polymerisation catalysed by imido‐supported molybdenum and tungsten alkylidenes. A summary of the “design principles” that have been employed in the development of certain imido‐based Ziegler–Natta catalysts is presented, followed by a comprehensive survey of the literature in the title area.
Cationic Alkyl Complexes of the Rare‐Earth Metals: Synthesis, Structure, and Reactivity
Authors: Arndt Stefan , Okuda Jun
Published: February 2005

Cationic alkyl complexes of the rare‐earth metals [LnRm(L)n](3–m)+ (R=alkyl; m=1, 2; L=Lewis base) were virtually unknown species until recently. Because of their increased Lewis acidity/electrophilicity they should have considerable potential as homogeneous catalysts in olefin polymerization and in organic transformations. They can be generated by treating the neutral rare‐earth metal precursors containing at least two alkyl groups R with suitable Lewis or Brønsted acids in the presence of weakly coordinating anions. Not only monocationic but also dicationic alkyl derivatives have been shown to be accessible. In the context of modeling homogeneous ethylene polymerization using a mixture consisting of LnR3/AlR3/[NMe2HPh][B(C6F5)4], such dications were discovered. Some thermally robust examples of mono‐ and dicationic alkyl complexes have been structurally characterized as solvent‐separated ion pairs. Neutral and monoanionic macrocycles such as crown ethers or aza‐crown ethers as well as amidinato, β‐diketiminato, and substituted cyclopentadienyl ligands are suitable ancillary ligands to stabilize the cationic alkyl fragments.
Ligand Architecture on Stereocontrol of Half‐Metallocene Benzylidene Complexes of Tantalum
Authors: Mashima Kazushi
Published: February 2005

This brief review discloses our studies on half‐metallocene benzylidene complexes of tantalum bearing 1,3‐butadiene, 2,3‐dimethyl‐1,3‐butadiene, o‐xylylene, 1,4‐diaryl‐1,4‐diaza‐1,3‐butadiene, or 1‐aryl‐4‐phenyl‐1‐aza‐1,3‐butadiene as an auxiliary ligand. These auxiliary ligands can control the stereochemistry of the benzylidene moiety and induce intriguing reactivity. Furthermore, the butadiene and o‐xylylene complexes catalyze ring opening metathesis polymerization of norbornene to respectively give polymers with cis‐ and trans‐CC bonds. Such selectivity can be attributed to control of the stereochemistry of the propagating alkylidene chain end by the auxiliary ligand: the butadiene complex favors the anti‐rotamer while the o‐xylylene complex favors the syn‐one.
Exploring Routes to Tantalum(V) Alkylidene Complexes Supported by Amine Tris(phenolate) Ligands
Authors: Groysman Stanislav , Goldberg Israel , Kol Moshe , Genizi Elisheva , Goldschmidt Zeev
Published: February 2005

Two basic organometallic species, tris(neopentyl)mono(neopenylidene)tantalum and pentabenzyltantalum, were evaluated as starting materials on the route to alkyl and alkylidene complexes with amine tris(phenolate) ligands. The reaction of the former with the ligand precursor proceeded via the addition of the OH functionality to the TaC double bond at the first step, forming a sterically congested tetraneopentyl complex, that was characterized by X‐ray crystallography. In contrast, the reaction of the less bulky pentabenzyltantalum with a variety of the ligand precursors led directly and in a high yield to the dibenzyl Ta(V) complexes. These species were surprisingly stable toward thermolysis, decomposing only at 120–130 °C after prolonged periods of time. The unexpected product of this decomposition was found to be a dinuclear μ‐benzylidene Ta(V) complex.
Effect of Cyclopentadienyl Fragment in Copolymerization of Ethylene with Cyclic Olefins Catalyzed by Non‐Bridged (Aryloxo)(cyclopentadienyl)titanium(IV) Complexes
Authors: Wang Wei , Tanaka Tatsuo , Tsubota Miki , Fujiki Michiya , Yamanaka Shozo , Nomura Kotohiro
Published: February 2005

The effect of the cyclopentadienyl fragment in the copolymerization of ethylene with norbornene (NBE) by various non‐bridged (aryloxo)(cyclopentadienyl)titanium(IV) complexes of the type, Cp′TiCl2(OAr) [Cp′=indenyl (1), C5Me5 (Cp*, 2), t‐BuC5H4 (3), 1,2,4‐Me3C5H2 (4); OAr=O‐2,6‐i‐Pr2C6H3], MAO catalyst systems has been explored. The catalytic activity and the NBE incorporation were highly dependent upon substituent on Cp′ employed, and 1 exhibited both a remarkable catalytic activity and an efficient NBE incorporation, affording high molecular weight polymers with unimodal molecular weight distributions. NBE repeat units were observed in the resultant poly(ethylene‐co‐NBE)s prepared by 1, 3, and 4, and the degree of NBE dyads as well as alternating sequences was strongly influenced by the Cp′ employed. These complexes (1,3,4) also exhibited high catalytic activities for ethylene/cyclopentene (CPE) copolymerization, but the CPE incorporation by 1 was less efficient than the NBE incorporation under the same conditions. The ab initio density functional (DF) molecular orbital (MO) methods were utilized to explore the effect of substituents on Cp′ toward the catalytic activity, the NBE incorporation and the monomer sequence distribution. Good correlations between the ΔEcoordEt (coordination energy of ethylene) after NBE insertion and the activity, and between ΔEcoordNBE (coordination energy of NBE) after ethylene (or NBE insertion) and NBE content were observed, strongly suggesting that the capability producing NBE repeat units was dependent upon ΔEcoordNBE after NBE insertion.
Enantioselective Alkynylation of Aromatic Ketones Catalyzed by New Chiral Oxazolidine Ligands
Authors: Kang Yong‐Feng , Liu Lei , Wang Rui , Zhou Yi‐Feng , Yan Wen‐Jin
Published: February 2005

New chiral oxazolidine ligands have been derived conveniently from natural amino acids in good yields. Their use in the enantioselective addition of phenylacetylene to aromatic ketones has been tested with the best ee being up to 88%. We provide a simple, practical and inexpensive method to generate chiral tertiary propargylic alcohols.
A General Copper‐Promoted Coupling of Sulfoximines with Vinyl Bromides
Authors: Dehli Juan R. , Bolm Carsten
Published: February 2005

Vinylsulfoximines have been prepared in high yields by copper‐promoted coupling reactions starting from NH‐sulfoximines and vinyl bromides.
General Approach for Template‐Directed Synthesis of Macroheterocycles by Ring‐Closing Metathesis (RCM)
Authors: Chuchuryukin Alexey V. , Chase Preston A. , Dijkstra Harm P. , Suijkerbuijk Bart M. J. M. , Mills Allison M. , Spek Anthony L. , van Klink Gerard P. M. , van Koten Gerard
Published: February 2005

A general method to prepare macroheterocycles is reported in which a rigid symmetric platinated tris‐pincer tricationic complex (3) is used as a template. The system uses bisolefin functionalized pyridine ligands (1, 2) which selectively bind to the three platinum centers of the template resulting in pre‐organization of the olefinic tails. By subjecting these pre‐organized complexes (4) to olefin metathesis reaction conditions, the olefinic tails were interconnected affording several macroheterocycles of different compositions and sizes. Various pyridines with different substitution patterns (2,6‐ and 3,5‐disubstituted) and different olefinic tails (aliphatic, polyether, and styryl) were synthesized and used in the cyclization reactions, showing the diversity of this method. It was found that only the use of 2,6‐disubstituted pyridines resulted in the formation of the desired macrocycles while 3,5‐difunctionalized pyridines gave only pyridinophane formation. Furthermore, the length of the olefinic tails needs to be at least eleven atoms (C or O) in order to suppress oligomerization in favor of macrocycle formation. Yields of up to 70% of the macrocycles were obtained using the first‐generation [Cl2(Cy3P)2RuCHPh] or second‐generation [Cl2(Cy3P)(IMes)RuCHPh] Grubbs' catalysts. Reactions of the platinated pincer pyridines with Schrock Mo‐based metathesis catalysts results in exclusive olefin isomerization and no productive metathesis. The generated macrocycles (hosts) could effectively be separated from the template by addition of aqueous sodium chloride and reattached to the (recycled) template (guest). The X‐ray structure determination of host‐guest complex10is the definite proof for this reattachment and the perfect cyclic structure of the macrocycle.
[Zinc‐Diamine]‐Catalyzed Hydrosilylation of Ketones in Methanol. New Developments and Mechanistic Insights
Authors: Bette Virginie , Mortreux André , Savoia Diego , Carpentier Jean‐François
Published: February 2005

The Zn‐promoted direct reduction of various ketones, including alkyl aryl ketones, α‐ and β‐keto esters, α‐ and β‐keto amides, into the corresponding alcohols with polymethylhydrosiloxane (PMHS) in protic conditions is reported. The reaction proceeds chemoselectively under smooth conditions, with simple catalyst combinations based on a zinc precursor [ZnEt2, Zn(OMe)2, Zn(OH)2] and a 1,2‐diamine ligand, e.g., N,N′‐dibenzylethylenediamine (dbea). The reaction rates are significantly faster than under aprotic conditions. For β‐keto esters and amides, the use of an excess of PMHS is required. Moderate enantioselectivities (ee up to 55%) have been obtained using a variety of enantiopure diamine ligands. Two mechanisms are proposed for the new catalytic reaction, on the basis of the synthesis of [(diamine)Zn(alkoxide)2] complexes which are models of the possible reaction intermediates and a study of their activity.
Heterogenization of Organometallic Molybdenum Complexes with Siloxane Functional Groups and their Catalytic Application
Authors: Sakthivel Ayyamperumal , Zhao Jin , Hanzlik Marianne , Chiang Anthony S. T. , Herrmann Wolfgang A. , Kühn Fritz E.
Published: February 2005

η5‐CpMo(CO)3R complexes containing siloxane functional groups [(CH2)3Si(OMe)3 or (CH2)Si(OEt)3] attached to either the cyclopentadiene ligand or directly to Mo were grafted on the mesoporous materials MCM‐41 and MCM‐48 by reaction of the OR (R=Me, Et) moieties in the silane ligand and surface silanol groups (Si‐OH). For the sake of comparison mesoporous materials modified with silane groups were reacted with Na+[CpMo(CO)3]−. The XRD, N2 adsorption‐desorption, and TEM analyses provide strong evidence that the mesoporous structure of the supporting material retains its long‐range ordering throughout the grafting process, despite significant reductions in surface area, pore volume and pore size. The appearance of strong IR bands around 2016 and 1956 cm−1 on the grafted samples also shows that the η5‐CpMo(CO)3R complexes have been successfully grafted. Elemental analysis reveals that the grafted samples contain 0.3–3.5 wt % Mo. 29Si CP MAS‐NMR spectra give clear evidence for a reduction in the numbers of the Q3 and Q2 sites. The formation of new peaks around −49.8, −57.9, and −66.2 ppm (T1, T2, and T3) indicates esterification of silanol groups by the alkoxy groups of the silane ligand. Both the in situ and ex situ prepared samples show good catalytic activity for the epoxidation of cyclooctene.
Room Temperature Liquid Salts of Cr and Mo as Self‐Supported Oxidants
Authors: Noguera Gladys , Mostany Jorge , Agrifoglio Giuseppe , Dorta Romano
Published: February 2005

Room temperature liquid salts of Cr and Mo were synthesized and fully characterized including cyclic voltammetry of the neat Mo salt. These liquid salts were used as self‐supported reagents for the oxidation of alcohols (under solvent‐free and biphasic conditions) and their potential for biphasic self‐supported catalytic applications was demonstrated.
Convenient and Inexpensive Synthesis of (1R,2R)‐ trans‐1‐Amino‐6‐nitroindan‐2‐ol
Authors: Kozhushkov Sergei I. , Yufit Dmitrii S. , de Meijere Armin
Published: February 2005

Racemic trans‐1‐amino‐6‐nitroindan‐2‐ol (rac‐1) has been prepared in five steps from inexpensive indene (7) in 96% overall yield. The key step was a direct nitration of the known trans‐1‐aminoindan‐2‐ol (rac‐9) which gave sulfuric acid mono‐(rac‐trans‐1‐amino‐6‐nitroindan‐2‐yl) ester (rac‐10) in quantitative yield. The latter was quantitatively converted into rac‐1 by treatment with aqueous 6 N HCl and then ammonia solutions. The same transformations of (1R,2R)‐9 [prepared by deracemization of rac‐9 with (−)‐dibenzoyl‐L‐tartaric acid (DBT)] proceeded without loss of the optical activity. Deracemization of rac‐1 applying (+)‐(S)‐L‐mandelic acid (MA) furnished (1R,2R)‐1 and (1S,2S)‐1 in 34 and 17% yield, respectively, with e.e. ≥ 98 and 97.6%, respectively. Procedures for recycling of the chiral auxiliaries DBT and MA are also described. The structures of key intermediates were confirmed by X‐ray crystal structure analysis.
A General and Efficient Method for the Synthesis of Silyl‐Protected Arenethiols from Aryl Halides or Triflates
Authors: Kreis Michael , Bräse Stefan
Published: February 2005

An improved palladium‐catalyzed synthesis of silyl‐protected arenethiols has been developed. This method is particularly useful because of its experimental simplicity, high generality and high level of functional group toleration. The first synthesis of enantiomerically pure [2.2]paracyclophane‐4‐thiol was realized employing this method.
Synthesis of (all‐rac)‐α‐Tocopherol in Supercritical Carbon Dioxide: Tuning of the Product Selectivity in Batch and Continuous‐Flow Reactors
Authors: Kokubo Yoshiaki , Hasegawa Aiko , Kuwata Shigeki , Ishihara Kazuaki , Yamamoto Hisashi , Ikariya Takao
Published: February 2005

α‐Tocopherol was synthesized using a condensation reaction of 2,3,6‐trimethylhydroquinone with isophytol in supercritical CO2 using batch and continuous–flow reactors. In the batch reaction catalyzed by a fluorinated molecular catalyst bearing strong Brønsted acidity, C6F5CHTf2 (Tf=SO2CF3), an increase in the CO2 pressure causes a marked increase in the product selectivity for α‐tocopherol, albeit with a slight decrease in the product yield. The solubility measurements by extraction experiments and the supercritical fluid NMR (scNMR) indicate that the homogeneous and non‐polar reaction phase in scCO2 is crucial to obtain α‐tocopherol with high selectivity. A continuous flow scCO2 process for the condensation reaction can be performed with a strong acid resin, Amberlyst 15, as a solid acid catalyst to give the desired product with high selectivity.
Organic Base‐Mediated Condensation of Pyridinecarboxaldehydes to Azachalcones
Authors: Downs Laura E. , Wolfe Derek M. , Schreiner Peter R.
Published: February 2005

A DBU‐mediated aldol condensation‐dehydration sequence has been used to prepare a series of synthetically important substituted 2‐ and 3‐azachalcones. Michael products that typically accompany this sequence with inorganic bases were not observed in this protocol of high practical value.
Asymmetric Synthesis of Acyclic Amines Through Zr‐ and Hf‐Catalyzed Enantioselective Alkylzinc Reagents to Imines
Authors: Akullian Laura C. , Porter James R. , Traverse John F. , Snapper Marc L. , Hoveyda Amir H.
Published: February 2005

Readily available chiral amino acid‐based ligands are used in metal‐catalyzed additions of alkylzinc reagents to various aromatic and aliphatic imines; the desired amine products are formed efficiently and in high levels of optical purity. In cases where the more Lewis acidic Zr salts afford lower efficiency, Hf‐based catalysts deliver significantly higher yields with similar enantioselectivities. Critical structural features of the N‐activating groups as well as the optimal chiral ligands are discussed. A mechanistic working model is presented to rationalize the existing data and to serve as a predictive tool.
Influence of mass transfer in distillation: Feasibility and design
Authors: Baur R. , Krishna R. , Taylor R.
Published: February 2005

The influence is considered of mass transfer on distillation column design. The column design equations incorporating mass‐transfer effects are similar to the conventional design equations and are as easy to solve numerically. Mass‐transfer effects do not influence pinch‐point curves and pitchfork distillation boundaries. Mass transfer does, however, change the composition trajectories, which might thus cross the pinch‐point curves. Inclusion of mass transfer in the design equations allows us to estimate the actual number of stages (or the column height). The curvature of composition trajectories may have a significant impact on the total number of stages and on the feed stage location. Mass‐transfer effects do not influence the minimum reflux for columns involving a very sharp split. However, and contrary to previous reports, mass‐transfer effects may strongly affect the minimum reflux for less than very sharp separations. Mass‐transfer effects should be taken into consideration when trace components are a concern. A feasible design based on residue curve maps might be rejected by a design method based on mass transfer. More important, however, the converse also is true. © 2005 American Institute of Chemical Engineers AIChE J, 51: 854–866, 2005
Mass and heat transfer modeling of a physical vapor deposition effusion source
Authors: Junker S. Tobias , Birkmire Robert W. , Doyle Francis J.
Published: February 2005

The effusion sources modeled in this article are part of a continuous process for production of thin‐film photovoltaic modules. Industrial production requires tight control of the vapor flow rates during long run times. A dynamic model is developed to provide physical insight, facilitate simulation studies, and to be incorporated into model‐based control schemes. Prediction of the vapor flow rate requires both the mass and energy balance to be solved. Model parameters are estimated based on literature and experimental data, and the entire model is shown to be consistent with independent experimental data. © 2005 American Institute of Chemical Engineers AIChE J, 51: 878–894, 2005
Multiscale models of sweep gas and porous support effects on zeolite membranes
Authors: Skoulidas Anastasios I. , Sholl David S.
Published: February 2005

Existing detailed models of gas permeation through zeolite membranes have focused on adsorption and diffusion within zeolite crystals. Practical zeolite membranes, however, are typically grown as thin films on porous supports and are often studied experimentally in the presence of a sweep gas in addition to the permeating species of interest. We have used a combination of atomically detailed and continuum models to examine the impact of sweep gases and porous supports on permeation of CH4 through silicalite membranes at room temperature. The adsorption and transport properties of the gas mixture inside the zeolite are treated using atomically detailed models, whereas transport in the porous support is treated using well‐validated continuum models. Our results indicate that the effect of He as a sweep gas on unsupported membranes is minor. In many cases, the use of a porous support when no sweep gas is present also has only negligible effects compared to that of an unsupported membrane. When a sweep gas and a porous support are present, however, strong deviations from the permeation properties of an equivalent unsupported membrane with no sweep gas can occur, and these effects can depend strongly on whether the support faces the feed or permeate side of the process. These observations are related to existing experimental studies of gas permeation through zeolite membranes. © 2005 American Institute of Chemical Engineers AIChE J, 51: 867–877,2005
Rapid generation of composition profiles for reactive and extractive cascades
Authors: Chin James , Lee Jae W.
Published: February 2005

A quick method for estimating composition profiles for reactive and extractive cascades in a double‐feed column without stage calculations is presented. This profile estimation is based on the feasibility and pinch point analyses. The trajectories of pinch points are determined with material balance equations and phase and reaction equilibrium data. From these pinch point trajectories, the ranges of feasible external reflux ratios and required entrainer flow rates are calculated for a given reaction extent and product purity. Then, for given external reflux ratios, heat balance constraints are imposed to determine the positions of pinch points. Finally, using the internal reflux ratios of these pinch points, manifolds of possible composition profiles are generated. Composition profiles of a reactive/extractive cascade can lie in the section of the reaction equilibrium surface where the internal reflux ratio of a saddle pinch is between the upper and lower bounds of the internal reflux ratio. © 2005 American Institute of Chemical Engineers AIChE J, 51: 922–930, 2005
Crystallographic report: Crystal and molecular structure of Ph3GeO2CC4H3O
Authors: Yin Han‐Dong , Wang Chuan‐Hua
Published: February 2005

The germanium atom in the title compound is in a distorted tetrahedral geometry defined by an oxygen donor, derived from an effectively monodentate carboxylate ligand, and three ipso‐carbon atoms from the phenyl substituents. Copyright © 2005 John Wiley & Sons, Ltd.
Crystallographic report: Hydroxytrimethylarsonium iodide, [Me3AsOH]I
Authors: Patrick Brian O. , Sun Hongsui , Fricke Michael W. , Cullen William R.
Published: February 2005

Hydroxytrimethylarsonium iodide, [Me3AsOH]I, was obtained from the reaction of Me2AsI and MeI in strong basic aqueous solution. The arsenic atom, lying on a mirror plane, is surrounded by one OH and three Me groups, forming a tetrahedral centre. Copyright © 2005 John Wiley & Sons, Ltd.
Crystallographic report: Dimethyl‐2‐phenylethan‐2‐olamine cyanoborane
Authors: Takrouri Khuloud , Shalom Eli , Goldberg Israel , Katzhendler Jehoshua , Srebnik Morris
Published: February 2005

The structure of the title compound reveals the geometry around the boron atom to be tetrahedral, and the BCN moiety has a bent geometry. Copyright © 2005 John Wiley & Sons, Ltd.
Crystallographic report: Dipyridium mercaptoacetotrichlorophenylstannate
Authors: Zhong Gui‐Yun , Song Hai‐Bin , Sun Li‐Juan , Xie Qing‐Lan
Published: February 2005

The tin atom in the anion of [C5H5NH]2[PhSn(SCH2COO)Cl3] is six‐coordinated within an octahedral geometry defined by a CCl3OS donor set; the cations and anion interact via hydrogen bonds. Copyright © 2005 John Wiley & Sons, Ltd.
Crystallographic report: Chloro[1,3‐bis[2‐[2‐[(4‐methoxybenzyl) amino]ethylamino]]‐2‐propanol]zinc(II) chloride hydrate, [(C23H36N4O3)ZnCl]Cl·H2O
Authors: Liu Xueting , Xie Yongshu , Liu Qingliang
Published: February 2005

The zinc(II) center in the molecule of [(C23H36N4O3)ZnCl]Cl·H2O is coordinated by four nitrogen atoms of HL (1,3‐bis[2‐[2‐[(4‐methoxybenzyl) amino]ethylamino]]‐2‐propanol) and one chloro anion. The coordination moieties are connected by hydrogen bonds to form a one‐dimensional structure. Copyright © 2005 John Wiley & Sons, Ltd.