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971.
Synthesis,Structure, and Reactivity of Anionic sp2–sp3 Diboron Compounds: Readily Accessible Boryl Nucleophiles 下载免费PDF全文
Sabrina Pietsch Dr. Emily C. Neeve Dr. David C. Apperley Dr. Rüdiger Bertermann Dr. Fanyang Mo Di Qiu Dr. Man Sing Cheung Dr. Li Dang Prof. Dr. Jianbo Wang Prof. Dr. Udo Radius Prof. Dr. Zhenyang Lin Dr. Christian Kleeberg Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(19):7082-7098
Lewis base adducts of tetra‐alkoxy diboron compounds, in particular bis(pinacolato)diboron (B2pin2), have been proposed as the active source of nucleophilic boryl species in metal‐free borylation reactions. We report the isolation and detailed structural characterization (by solid‐state and solution NMR spectroscopy and X‐ray crystallography) of a series of anionic adducts of B2pin2 with hard Lewis bases, such as alkoxides and fluoride. The study was extended to alternative Lewis bases, such as acetate, and other diboron reagents. The B(sp2)–B(sp3) adducts exhibit two distinct boron environments in the solid‐state and solution NMR spectra, except for [(4‐tBuC6H4O)B2pin2]?, which shows rapid site exchange in solution. DFT calculations were performed to analyze the stability of the adducts with respect to dissociation. Stoichiometric reaction of the isolated adducts with two representative series of organic electrophiles—namely, aryl halides and diazonium salts—demonstrate the relative reactivities of the anionic diboron compounds as nucleophilic boryl anion sources. 相似文献
972.
Udo Schmidt Philip C. Zehetmaier Bernhard Rieger 《Macromolecular rapid communications》2010,31(6):545-548
Poly(dimethylsiloxane) copolymers were synthesized directly from AA/BB monomers employing a CuAAC reaction (click chemistry) in a polyaddition approach. Using organic dialkynes and oligo(siloxane)s end‐functionalized with azide moieties it was possible to obtain siloxane‐based copolymers with TPE properties by click chemistry for the first time. As seen from DSC experiments, properties were strongly dependent on the incorporated organic comonomer.
973.
Synthesis and Characterization of Organic Dyes with Various Electron‐Accepting Substituents for p‐Type Dye‐Sensitized Solar Cells 下载免费PDF全文
Martin Weidelener Dr. Satvasheel Powar Hannelore Kast Dr. Ze Yu Dr. Pablo P. Boix Dr. Chen Li Prof. Klaus Müllen Dr. Thomas Geiger Dr. Simon Kuster Prof. Frank Nüesch Prof. Udo Bach Dr. Amaresh Mishra Prof. Peter Bäuerle 《化学:亚洲杂志》2014,9(11):3251-3263
Four new donor‐π‐acceptor dyes differing in their acceptor group have been synthesized and employed as model systems to study the influence of the acceptor groups on the photophysical properties and in NiO‐based p‐type dye‐sensitized solar cells. UV/Vis absorption spectra showed a broad range of absorption coverage with maxima between 331 and 653 nm. Redox potentials as well as HOMO and LUMO energies of the dyes were determined from cyclic voltammetry measurements and evaluated concerning their potential use as sensitizers in p‐type dye‐sensitized solar cells (p‐DSCs). Quantum‐chemical density functional theory calculations gave further insight into the frontier orbital distributions, which are relevant for the electronic processes in p‐DSCs. In p‐DSCs using an iodide/triiodide‐based electrolyte, the polycyclic 9,10‐dicyano‐acenaphtho[1,2‐b]quinoxaline (DCANQ) acceptor‐containing dye gave the highest power conversion efficiency of 0.08 %, which is comparable to that obtained with the perylenemonoimide (PMI)‐containing dye. Interestingly, devices containing the DCANQ‐based dye achieve a higher VOC of 163 mV compared to 158 mV for the PMI‐containing dye. The result was further confirmed by impedance spectroscopic analysis showing higher recombination resistance and thus a lower recombination rate for devices containing the DCANQ dye than for PMI dye‐based devices. However, the use of the strong electron‐accepting tricyanofurane (TCF) group played a negative role in the device performance, yielding an efficiency of only 0.01 % due to a low‐lying LUMO energy level, thus resulting in an insufficient driving force for efficient dye regeneration. The results demonstrate that a careful molecular design with a proper choice of the acceptor unit is essential for development of sensitizers for p‐DSCs. 相似文献
974.
The diols 2 and 3, available in one step from cycloocta-1,5-diene, are selectively acetylated at the (R)-centers using Candida rugosa lipase to give the corresponding enantiopure compounds. In contrast, the (S,S)-enantiomer of 11 is transformed under identical conditions. The stereoselectivity of the lipase has been investigated by modeling of the transition state geometries at the active site of the enzyme. 相似文献
975.
Dorota Koziej Nicolae Brsan Udo Weimar Jacek Szuber Kengo Shimanoe Noboru Yamazoe 《Chemical physics letters》2005,410(4-6):321-323
Resistance measurements and direct spectroscopic investigations were used to monitor the surface reaction path between oxygen and water at the surface of SnO2. The experiments were carried out at high sensor operation temperature (330 and 400 °C) and at a constant background of water vapour. We found that there is a significant interaction between adsorbed oxygen ions and water vapour, which results in formation of terminal hydroxyl groups on tin dioxide surface. This observation is an evidence of water–oxygen interaction and so brings a new insight to the mechanistic modelling of the sensing with tin dioxide based sensors. 相似文献
976.
Tjipke de Beer Paul Besoo Gerard Ph. Hoornweg Nel H. Velthorst Udo A.Th. Brinkman Cees Gooijer 《Analytica chimica acta》1999,390(1-3):55-64
The performance of forward-scattering degenerate four-wave mixing (F-D4WM) in the mid-ultraviolet (UV) region (351 nm) as a detection technique for micro-column liquid chromatography (μLC) is studied, using nitro-substituted polycyclic aromatic hydrocarbons (NO2-PAHs) and amino-substituted anthraquinones (AAQs) as test compounds. When using round capillaries, the concentration limits of detection (LOD) for the NO2-PAHs were 20–70-fold better compared with absorption detection using a U-shaped detector cell. The final result is influenced by photochemical degradation during 351 nm F-D4WM detection. Furthermore, it is demonstrated that the use of recently commercially available square capillaries (i.e., capillaries with both a square cross section and a square bore) instead of round ones is quite suitable for F-D4WM detection. The square capillary (internal dimensions, 75×75 μm2; external dimensions 300×300 μm2) did not cause significant chromatographic band broadening in μLC. The angle of incidence of the laser light should be 56°, thus fulfilling the Brewster condition at the air–quartz boundary. Using this approach for the AAQs, compounds not prone to significant photodegradation under the experimental conditions, a further 4-fold improvement was achieved. As a result, the overall gain in concentration LOD for 2-amino-9,10-anthraquinone (molar absorptivity 4000 M−1 cm−1 at 351 nm) was from 4 to 0.05 μM, and baseline irregulations were reduced. 相似文献
977.
Charles E. Kientz Jan P. Langenberg Gerhardus J. de Jong Udo A. Th. Brinkman 《Journal of separation science》1991,14(7):460-464
Microcolumn liquid chromatography (micro-LC) of some chiral organophosphorus pesticides has been studied using Chiralcel OD columns and simultaneous ultraviolet (UV) and phosphorus selective detection, the latter by means of a micro-UV cell coupled on-line to a thermionic detector (TID). Micro-LC showed a ca. 5-fold improved separation impedance, a ca. 1.8-fold increased column permeability, and greater inertness compared with conventional LC. By using the TID, organophosphorus pesticides could be satisfactorily determined at trace levels, the detection limit being 4 pg/s of phosphorus. The response of the micro-LC-TID system is linear in the range of 0.05–20 ng (r = 0.9994). 相似文献
978.
Elise C. Goosens Dirk de Jong Gerhardus J. de Jong Udo A. Th. Brinkman 《Journal of separation science》1997,20(6):325-332
The applicability of a liquid-liquid extraction system which is coupled on-line with a capillary gas chromatograph was studied for environmental and ecotoxicological analyses. The optimized and automated system was used for the determination of apolar and rather non-volatile organic compounds in aqueous samples. Relevant aspects of sample introduction, phase separation and selection of extraction solvent are discussed. Three routine-tipe applications are described, viz. an improved method for the determination of hexachlorocyclohexanes in ground water and the determination of the so-called NCC-ether and ACC-ether in ecotoxicological studies. Depending on the application studied, the concentration levels varied from 0.1 to 6000 μg/I, using ECD and/or FID detection. Typical coefficients of variation obtained with the total extraction–GC procedure were 2–25%. The system was found to be rugged, it saves time compared with set-ups involving off-line liquid-liquid extraction and considerably reduces the manual work load. 相似文献
979.
Dr. Yudha P. Budiman Sabine Lorenzen Zhiqiang Liu Prof. Dr. Udo Radius Prof. Dr. Todd B. Marder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(11):3869-3874
Catalytic C−X borylation of aryl halides containing two ortho-fluorines has been found to be challenging, as most previous methods require stoichiometric amounts of base and the polyfluorinated aryl boronates suffer from protodeboronation, which is accelerated by ortho-fluorine substituents. Herein, we report that a combination of Pd(dba)2 (dba=dibenzylideneacetone) with SPhos (2-dicyclohexylphosphino-2’,6’-dimethoxybiphenyl) as a ligand is efficient to catalyze the C-Cl borylation of aryl chlorides containing two ortho-fluorine substituents. This method, conducted under base-free conditions, is compatible with the resulting di-ortho-fluorinated aryl boronate products which are sensitive to base. 相似文献
980.
Steffen A. Föhrenbacher Mirjam J. Krahfuss Ludwig Zapf Dr. Alexandra Friedrich Dr. Nikolai V. Ignat'ev Prof. Dr. Maik Finze Prof. Dr. Udo Radius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(10):3504-3516
Fluoride abstraction from different types of transition metal fluoride complexes [LnMF] (M=Ti, Ni, Cu) by the Lewis acid tris(pentafluoroethyl)difluorophosphorane (C2F5)3PF2 to yield cationic transition metal complexes with the tris(pentafluoroethyl)trifluorophosphate counterion ( FAP anion, [(C2F5)3PF3]−) is reported. (C2F5)3PF2 reacted with trans-[Ni(iPr2Im)2(ArF)F] (iPr2Im=1,3-diisopropylimidazolin-2-ylidene; ArF=C6F5, 1 a ; 4-CF3-C6F4, 1 b ; 4-C6F5-C6F4, 1 c ) through fluoride transfer to form the complex salts trans-[Ni(iPr2Im)2(solv)(ArF)] FAP ( 2 a - c[solv] ; solv=Et2O, CH2Cl2, THF) depending on the reaction medium. In the presence of stronger Lewis bases such as carbenes or PPh3, solvent coordination was suppressed and the complexes trans-[Ni(iPr2Im)2(PPh3)(C6F5)] FAP ( trans -2 a[PPh3] ) and cis-[Ni(iPr2Im)2(Dipp2Im)(C6F5)] FAP ( cis -2 a[Dipp2Im] ) (Dipp2Im=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were isolated. Fluoride abstraction from [(Dipp2Im)CuF] ( 3 ) in CH2Cl2 or 1,2-difluorobenzene led to the isolation of [{(Dipp2Im)Cu}2]2+2 FAP− ( 4 ). Subsequent reaction of 4 with PPh3 and different carbenes resulted in the complexes [(Dipp2Im)Cu(LB)] FAP ( 5 a – e , LB=Lewis base). In the presence of C6Me6, fluoride transfer afforded [(Dipp2Im)Cu(C6Me6)] FAP ( 5 f ), which serves as a source of [(Dipp2Im)Cu)]+. Fluoride abstraction of [Cp2TiF2] ( 7 ) resulted in the formation of dinuclear [FCp2Ti(μ-F)TiCp2F] FAP ( 8 ) (Cp=η5-C5H5) with one terminal fluoride ligand at each titanium atom and an additional bridging fluoride ligand. 相似文献