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971.
Hexafluoroantimonic Acid Catalysis: Formal [3+2+2] Cycloaddition of Aziridines with Two Alkynes 下载免费PDF全文
Ming‐Bo Zhou Ren‐Jie Song Prof. Dr. Jin‐Heng Li 《Angewandte Chemie (International ed. in English)》2014,53(16):4196-4199
A practical method for the synthesis of azepine derivatives, a typical seven‐membered heterocyclic ring system, was developed and involves the use of hexafluoroantimonic acid to catalyze a formal [3+2+2] cycloaddition of aziridines with two alkynes. This method was applicable to two of the same or different terminal alkynes for the [3+2+2] cycloaddition with unactivated aziridines, and furnished the corresponding azepine derivatives in good yields with good levels of chemo‐ and regioselectivity. The mechanism was also discussed according to the results of the in situ HRMS and 1H NMR analysis. 相似文献
972.
Robust Inclusion Complexes of Crown Ether Fused Tetrathiafulvalenes with Li+@C60 to Afford Efficient Photodriven Charge Separation 下载免费PDF全文
Dr. Mustafa Supur Yuki Kawashima Dr. Karina R. Larsen Dr. Kei Ohkubo Prof. Jan O. Jeppesen Prof. Shunichi Fukuzumi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(43):13976-13983
Inclusion complexes of benzo‐ and dithiabenzo‐crown ether functionalized monopyrrolotetrathiafulvalene (MPTTF) molecules were formed with Li+@C60 ( 1? Li+@C60 and 2? Li+@C60). The strong complexation has been quantified by high binding constants that exceed 106 M ?1 obtained by UV/Vis titrations in benzonitrile (PhCN) at room temperature. On the basis of DFT studies at the B3LYP/6‐311G(d,p) level, the orbital interactions between the crown ether moieties and the π surface of the fullerene together with the endohedral Li+ have a crucial role in robust complex formation. Interestingly, complexation of Li+@C60 with crown ethers accelerates the intersystem crossing upon photoexcitation of the complex, thereby yielding 3(Li+@C60)*, when no charge separation by means of 1Li+@C60* occurs. Photoinduced charge separation by means of 3Li+@C60* with lifetimes of 135 and 120 μs for 1? Li+@C60 and 2? Li+@C60, respectively, and quantum yields of 0.82 in PhCN have been observed by utilizing time‐resolved transient absorption spectroscopy and then confirmed by electron paramagnetic resonance measurements at 4 K. The difference in crown ether structures affects the binding constant and the rates of photoinduced electron‐transfer events in the corresponding complex. 相似文献
973.
Mono‐ and Bis(pyrrolo)tetrathiafulvalene Derivatives Tethered to C60: Synthesis,Photophysical Studies,and Self‐Assembled Monolayers 下载免费PDF全文
Dr. Marta Vico Solano Dr. Eduardo Antonio Della Pia Dr. Martyn Jevric Christina Schubert Xintai Wang Dr. Cornelia van der Pol Prof. Dr. Anders Kadziola Prof. Dr. Kasper Nørgaard Prof. Dr. Dirk M. Guldi Prof. Dr. Mogens Brøndsted Nielsen Prof. Dr. Jan O. Jeppesen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9918-9929
A series of mono‐ (MPTTF) and bis(pyrrolo)tetrathiafulvalene (BPTTF) derivatives tethered to one or two C60 moieties was synthesized and characterized. The synthetic strategy for these dumbbell‐shaped compounds was based on a 1,3‐dipolar cycloaddition reaction between aldehyde‐functionalized MPTTF/BPTTF derivatives, two different tailor‐made amino acids, and C60. Electronic communication between the MPTTF/BPTTF units and the C60 moieties was studied by a variety of techniques including cyclic voltammetry and absorption spectroscopy. These solution‐based studies indicated no observable electronic communication between the MPTTF/BPTTF units and the C60 moieties. In addition, femtosecond and nanosecond transient absorption spectroscopy revealed, rather surprisingly, that no charge transfer from the MPTTF/BPTTF units to the C60 moieties takes place on excitation of the fullerene moiety. Finally, it was shown that the MPTTF–C60 and C60–BPTTF‐C60 dyad and triad molecules formed self‐assembled monolayers on a Au(111) surface by anchoring to C60. 相似文献
974.
Rachel Grainger Dr. Josep Cornella Dr. David C. Blakemore Dr. Igor Larrosa Dr. Josep M. Campanera 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16680-16687
A combined experimental and computational investigation on the Ag‐catalysed decarboxylation of benzoic acids is reported herein. The present study demonstrates that a substituent at the ortho position exerts dual effects in the decarboxylation event. On one hand, ortho‐substituted benzoic acids are inherently destabilised starting materials compared to their meta‐ and para‐substituted counterparts. On the other hand, the presence of an ortho‐electron‐withdrawing group results in an additional stabilisation of the transition state. The combination of both effects results in an overall reduction of the activation energy barrier associated with the decarboxylation event. Furthermore, the Fujita–Nishioka linear free energy relationship model indicates that steric bulk of the substituent can also exert a negative effect by destabilising the transition state of decarboxylation. 相似文献
975.
Mixed‐Ligand Catalysts: A Powerful Tool in Transition‐Metal‐Catalyzed Cross‐Coupling Reactions 下载免费PDF全文
Yuting Fan Mei Cong Ling Peng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(10):2698-2702
Transition‐metal‐catalyzed cross‐coupling reactions have fundamentally revolutionized organic synthesis, empowering the otherwise difficult to achieve products with rapid and convenient accesses alongside excellent yields. Within these reactions, ligands often play a critical role in specifically and effectively advocating the corresponding catalysis. Consequently, a myriad of ligands have been created and applied to make a fine tuning of electronic and steric effect of catalysts, remarkably promoting catalytic efficiency and applicability. The “mixed‐ligand” concept has recently emerged; by combining and capitalizing on the superiority of each individual ligand already available, an expedient way can be achieved to reach a larger extent of catalytic diversity and efficacy. Given the availability of a wealth of ligands, it is reasonable to have great expectations for the original application of mixed‐ligand catalytic systems and their important value in organic synthesis. 相似文献
976.
Back Cover: Amphiphilic Inclusion Spaces for Various Guests and Regulation of Fluorescence Intensity of 1,8‐Bis(4‐aminophenyl)anthracene Crystals (Chem. Eur. J. 11/2014) 下载免费PDF全文
977.
Dr. Thanh V. Nguyen Prof. Michael S. Sherburn 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):14991-14995
Shallow methylene‐bridged cavitands appended with simple H‐bond donor/acceptor groups are shown to bind aspirin. The structural features needed in a synthetic receptor for aspirin binding are defined. 相似文献
978.
Hans A. Laub Prof. Dr. Herbert Mayr 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(4):1103-1110
Kinetics of the reactions of benzhydrylium ions (Aryl2CH+) with the vinylsilanes H2C?C(CH3)(SiR3), H2C?C(Ph)(SiR3), and (E)‐PhCH?CHSiMe3 have been measured photometrically in dichloromethane solution at 20 °C. All reactions follow second‐order kinetics, and the second‐order rate constants correlate linearly with the electrophilicity parameters E of the benzhydrylium ions, thus allowing us to include vinylsilanes in the benzhydrylium‐based nucleophilicity scale. The vinylsilane H2C?C(CH3)(SiMe3), which is attacked by electrophiles at the CH2 group, reacts one order of magnitude faster than propene, indicating that α‐silyl‐stabilization of the intermediate carbenium ion is significantly weaker than α‐methyl stabilization because H2C?C(CH3)2 is 103 times more reactive than propene. trans‐β‐(Trimethylsilyl)styrene, which is attacked by electrophiles at the silylated position, is even somewhat less reactive than styrene, showing that the hyperconjugative stabilization of the developing carbocation by the β‐silyl effect is not yet effective in the transition state. As a result, replacement of vinylic hydrogen atoms by SiMe3 groups affect the nucleophilic reactivities of the corresponding C?C bonds only slightly, and vinylsilanes are significantly less nucleophilic than structurally related allylsilanes. 相似文献
979.
HOMO Stabilisation in π‐Extended Dibenzotetrathiafulvalene Derivatives for Their Application in Organic Field‐Effect Transistors 下载免费PDF全文
Dr. Yan Geng Dr. Raphael Pfattner Antonio Campos Prof. Wei Wang Dr. Olivier Jeannin Dr. Jürg Hauser Dr. Joaquim Puigdollers Prof. Stefan T. Bromley Prof. Silvio Decurtins Prof. Jaume Veciana Prof. Concepció Rovira Dr. Marta Mas‐Torrent Dr. Shi‐Xia Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16672-16679
Three new organic semiconductors, in which either two methoxy units are directly linked to a dibenzotetrathiafulvalene (DB‐TTF) central core and a 2,1,3‐chalcogendiazole is fused on the one side, or four methoxy groups are linked to the DB‐TTF, have been synthesised as active materials for organic field‐effect transistors (OFETs). Their electrochemical behaviour, electronic absorption and fluorescence emission as well as photoinduced intramolecular charge transfer were studied. The electron‐withdrawing 2,1,3‐chalcogendiazole unit significantly affects the electronic properties of these semiconductors, lowering both the HOMO and LUMO energy levels and hence increasing the stability of the semiconducting material. The solution‐processed single‐crystal transistors exhibit high performance with a hole mobility up to 0.04 cm2 V?1 s?1 as well as good ambient stability. 相似文献
980.
Halotriazolium Axle Functionalised [2]Rotaxanes for Anion Recognition: Investigating the Effects of Halogen‐Bond Donor and Preorganisation 下载免费PDF全文
James M. Mercurio Richard C. Knighton Dr. James Cookson Prof. Paul D. Beer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11740-11749
The anion‐templated synthesis of three novel halogen‐bonding 5‐halo‐1,2,3‐triazolium axle containing [2]rotaxanes is described, and the effects of altering the nature of the halogen‐bond donor atom together with the degree of inter‐component preorganisation on the anion‐recognition properties of the interlocked host investigated. The ability of the bromotriazolium motif to direct the halide‐anion‐templated assembly of interpenetrated [2]pseudorotaxanes was studied initially; bromide was found to be the most effective template. As a consequence, bromide anion templation was used to synthesise the first bromotriazolium axle containing [2]rotaxane, the anion‐binding properties of which, determined by 1H NMR spectroscopic titration experiments, revealed enhanced bromide and iodide recognition relative to a hydrogen‐bonding protic triazolium rotaxane analogue. Two halogen‐bonding [2]rotaxanes with bromo‐ and iodotriazolium motifs integrated into shortened axles designed to increase inter‐component preorganisation were also synthesised. Anion 1H NMR spectroscopic titration experiments demonstrated that these rotaxanes were able to bind halide anions even more strongly, with the iodotriazolium axle integrated rotaxane capable of recognising halides in aqueous solvent media. Importantly, these observations suggest that a halogen‐bonding interlocked host binding domain, in combination with increased inter‐component preorganisation, are requisite design features for a potent anion receptor. 相似文献