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991.
Ji Ma Yubin Fu Dr. Evgenia Dmitrieva Dr. Fupin Liu Dr. Hartmut Komber Dr. Felix Hennersdorf Dr. Alexey A. Popov Prof. Dr. Jan J. Weigand Dr. Junzhi Liu Prof. Dr. Xinliang Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(14):5686-5691
Three unprecedented helical nanographenes ( 1 , 2 , and 3 ) containing an azulene unit are synthesized. The resultant helical structures are unambiguously confirmed by X-ray crystallographic analysis. The embedded azulene unit in 2 possesses a record-high twisting degree (16.1°) as a result of the contiguous steric repulsion at the helical inner rim. Structural analysis in combination with theoretical calculations reveals that these helical nanographenes manifest a global aromatic structure, while the inner azulene unit exhibits weak antiaromatic character. Furthermore, UV/Vis-spectral measurements reveal that superhelicenes 2 and 3 possess narrow energy gaps ( 2 : 1.88 eV; 3 : 2.03 eV), as corroborated by cyclic voltammetry and supported by density functional theory (DFT) calculations. The stable oxidized and reduced states of 2 and 3 are characterized by in-situ EPR/Vis–NIR spectroelectrochemistry. Our study provides a novel synthetic strategy for helical nanographenes containing azulene units as well as their associated structures and physical properties. 相似文献
992.
Alexey Voronov Atsushi Urakawa Wouter van Beek Nikolaos E. Tsakoumis Hermann Emerich Magnus Rønning 《Analytica chimica acta》2014
Large datasets containing many spectra commonly associated with in situ or operando experiments call for new data treatment strategies as conventional scan by scan data analysis methods have become a time-consuming bottleneck. Several convenient automated data processing procedures like least square fitting of reference spectra exist but are based on assumptions. Here we present the application of multivariate curve resolution (MCR) as a blind-source separation method to efficiently process a large data set of an in situ X-ray absorption spectroscopy experiment where the sample undergoes a periodic concentration perturbation. MCR was applied to data from a reversible reduction–oxidation reaction of a rhenium promoted cobalt Fischer–Tropsch synthesis catalyst. The MCR algorithm was capable of extracting in a highly automated manner the component spectra with a different kinetic evolution together with their respective concentration profiles without the use of reference spectra. The modulative nature of our experiments allows for averaging of a number of identical periods and hence an increase in the signal to noise ratio (S/N) which is efficiently exploited by MCR. The practical and added value of the approach in extracting information from large and complex datasets, typical for in situ and operando studies, is highlighted. 相似文献
993.
Synthesis of 1,2,3,4-tetrazine 1,3-dioxides annulated with 1,2,3-triazoles and 1,2,3-triazole 1-oxides 总被引:1,自引:0,他引:1
Alexey A. Voronin Victor P. Zelenov Aleksandr M. Churakov Yurii A. Strelenko Ivan V. Fedyanin Vladimir A. Tartakovsky 《Tetrahedron》2014
1,2,3,4-Tetrazine 1,3-dioxides annulated with 1,2,3-triazoles and 1,2,3-triazole 1-oxides have been synthesized by the reaction of 4-amino-5-(tert-butyl-NNO-azoxy)-2-R-2H-1,2,3-triazoles (R=Me, i-Pr, t-Bu) and their 1-oxides (R=H, Me, Et, i-Pr) with the HNO3/H2SO4/Ac2O system. Their thermal stability, spectroscopic, and X-ray properties have been studied. 相似文献
994.
Fedor I. Zubkov Eugenia V. Nikitina Timur R. Galeev Vladimir P. Zaytsev Victor N. Khrustalev Roman A. Novikov Daria N. Orlova Alexey V. Varlamov 《Tetrahedron》2014
An efficient and versatile one-pot synthesis of 3,6a-epoxyisoindoles annelated with oxazine, oxazole, thiazine, thiazole, pyrimidine fragments and with their benzoannelated analogues is presented. The method is based on tandem N-acylation/intramolecular cycloaddition (the intramolecular Diels–Alder reaction of furan, IMDAF) reaction between α,β-unsaturated acid anhydrides and α-furyl substituted azaheterocycles. The latter can be easily prepared by condensation of diverse furfurals and 1,2- or 1,3-N,X-binucleophiles (aminoalcohols, aminothiols, diamines). The observed IMDAF reaction is stereoselective: exo-adducts are formed exclusively with large prevalence of one of the diastereoisomers. In most cases, the condensation/N-acylation/IMDAF reaction sequence may be carried out via a one-pot domino protocol. The scope and limitations of the proposed approach are thoroughly investigated. The obtained Diels–Alder adducts are attractive and useful substrates for further transformations. Fused isoindoles can be prepared from them in one-step by aromatization of the 7-oxabicyclo[2.2.1]heptene ring. Other transformations, including halogenation, ring cleavage, and Wagner–Meerwein skeletal rearrangement, are also demonstrated. The spatial structures of the obtained compounds have been established by X-ray diffraction analyses. 相似文献
995.
Extending Metal‐to‐Polyoxometalate Charge Transfer Lifetimes: The Effect of Heterometal Location
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Elliot N. Glass Dr. John Fielden Dr. Alexey L. Kaledin Dr. Djamaladdin G. Musaev Prof. Dr. Tianquan Lian Prof. Dr. Craig L. Hill 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(15):4297-4307
In an effort to develop robust molecular sensitizers for solar fuel production, the electronic structure and photodynamics of transition‐metal‐substituted polyoxometalates (POMs), a novel class of compound in this context, was examined. Experimental and computational techniques including femtosecond (fs) transient absorption spectroscopy have been used to study the cobalt‐containing Keggin POMs, [CoIIW12O40]6? ( 1 a ), [CoIIIW12O40]5? ( 2 a ), [SiCoII(H2O)W11O39]6? ( 3 a ), and [SiCoIII(H2O)W11O39]5? ( 4 a ), finding the longest lived charge transfer excited state so far observed in a POM and elucidating the electronic structures and excited‐state dynamics of these compounds at an unprecedented level. All species exhibit a bi‐exponential decay in which early dynamic processes with time constants in the fs domain yield longer lived excited states which decay with time constants in the ps to ns domain. The initially formed states of 1 a and 3 a are considered to result from metal‐to‐polyoxometalate charge transfer (MPCT) from CoII to W, while the longer‐lived excited state of 1 a is tentatively assigned to a localized intermediate MPCT state. The excited state formed by the tetrahedral cobalt(II) centered heteropolyanion ( 1 a ) is far longer‐lived (τ=420 ps in H2O; τ=1700 ps in MeCN) than that of 3 a (τ=1.3 ps), in which the single CoII atom is located in a pseudo‐octahedral addendum site. Short‐lived states are observed for the two CoIII‐containing heteropolyanions 2 a (τ=4.4 ps) and 4 a (τ=6.3 ps) and assigned solely to O→CoIII charge transfer. The dramatically extended lifetime for 1 a versus 3 a is ascribed to a structural change permitted by the coordinatively flexible central site, weak orbital overlap of the central Co with the polytungstate framework, and putative transient valence trapping of the excited electron on a single W atom, a phenomenon not noted previously in POMs. 相似文献
996.
Igor V. Kazakov Michael Bodensteiner Alexey Y. Timoshkin 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(3):312-314
The molecular structures of trichlorido(2,2′:6′,2′′‐terpyridine‐κ3N,N′,N′′)gallium(III), [GaCl3(C15H11N3)], and tribromido(2,2′:6′,2′′‐terpyridine‐κ3N,N′,N′′)gallium(III), [GaBr3(C15H11N3)], are isostructural, with the GaIII atom displaying an octahedral geometry. It is shown that the Ga—N distances in the two complexes are the same within experimental error, in contrast to expected bond lengthening in the bromide complex due to the lower Lewis acidity of GaBr3. Thus, masking of the Lewis acidity trends in the solid state is observed not only for complexes of group 13 metal halides with monodentate ligands but for complexes with the polydentate 2,2′:6′,2′′‐terpyridine donor as well. 相似文献
997.
Dmitri V. Konarev Alexey V. Kuzmin Salavat S. Khasanov Rimma N. Lyubovskaya 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(5):449-451
The title complex salt, (C16H36N)[MnBr(C32H16N8)] or (TBA)[MnIIBr(Pc)] (TBA is tetrabutylammonium and Pc is phthalocyaninate), has been obtained as single crystals by the diffusion technique and its crystal structure was determined using X‐ray diffraction. The high‐spin (S = ) [MnIIBr(Pc)]− macrocycle has a concave conformation, with an average equatorial Mn—N(Pc) bond length of 2.1187 (19) Å, an axial Mn—Br bond length of 2.5493 (7) Å and with the MnII cation displaced out of the 24‐atom Pc plane by 0.894 (2) Å. The geometry of the MnIIN4 fragment in [MnIIBr(Pc)]− is similar to that of the high‐spin (S = ) manganese(II) tetraphenylporphyrin (TPP) in [MnII(1‐MeIm)(TPP)] (1‐MeIm is 1‐methylimidazole). 相似文献
998.
Leonid G. Voskressensky Ekaterina A. SokolovaAlexey A. Festa Alexey V. Varlamov 《Tetrahedron letters》2013
A one-pot protocol towards previously unreported derivatives of thiochromeno [2′,3′:4,5] imidazo[2,1-a]isoquinoline via a domino reaction of isoquinoline-derived iminium salts and α-mercapto benzaldehydes is elaborated. 相似文献
999.
Alexey V. Salin Roza M. Aminova Vladimir I. Galkin 《International journal of quantum chemistry》2013,113(8):1086-1094
The structures of intermediates and transition states in the reaction of tertiary phosphines with unsaturated carboxylic acids have been calculated at the B3LYP level of theory using the 6‐31+G(d,p) basis set. Analysis of the results shows that [1,3]‐intramolecular migration of carboxylic proton to carbanionic center of generated zwitterionic intermediate is strongly kinetically unfavorable, and external proton‐donor source is essential to complete quaternization. A molecular cluster of the intermediate with one molecule of water has been modeled for intermolecular reaction pathway, but even in this case, the proton transfer remains to be the rate‐determining step that is in a good agreement with previous kinetic investigations on this reaction. The data obtained for this reaction have much in common with recent studies on the mechanisms of the Morita–Baylis–Hillman reaction and phosphine‐catalyzed [3+2] cycloaddition, which revealed paramount importance of proton‐transfer steps. © 2013 Wiley Periodicals, Inc. 相似文献
1000.
Pavlo S. Lebed' Pavlo O. Kos Andrey Tolmachev Mykhaylo V. Vovk Alexander N. Boyko Alexey Chekotylo 《合成通讯》2013,43(17):2343-2348
A Pd-mediated hydrogenation of ethyl 6-azidomethyl-1,2,3,4-tetrahydro-4-R-2-oxo-5-pyrimidinecarboxylates leads to the corresponding ethyl 6-aminomethyl1,2,3,4-tetrahydro-4-R-2-oxo-5-pyrimidinecarboxylates. The latter react with bis(trichloromethyl)carbonate, yielding the title ethyl 1,2,3,5,6,7-hexahydro-7-R-3,5-dioxoimidazo[1,5-c]pyrimidine-8-carboxylates. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献