- Mechanistic Studies on Propargyl Alcohol-Tethered Alkylidenecyclopropane with Aryldiazonium Salt Initiated by Visible Light
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This paper discloses the reaction mechanism of two consecutive but different visible light photo-induced chain processes for the rapid construction of spirobi[indene] skeletons. The first process is triggered by a photo-induced single-electron-transfer (SET) of an electron donor-accepter (EDA) complex. The second process is initiated by a direct SET process between aryldiazonium salt and the excited allenic intermediate. In these two processes, another SET took place respectively on the in situ formed radical intermediate to realize a redox-neutral outcome. The mechanistic studies have been carried out by control experiments, kinetic and spectroscopic analyses, deuterium labeling experiments to support these two chain processes.
- Liu, Jiaxin,Wei, Yin,Shi, Min
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- Proximity, photochemical reactivity, and intermolecular 1H-13C cross polarization in benzophenone-d10 and cyclohexane in the zeolite NaX
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The photochemistry, photophysics, and solid-state 13C CPMAS NMR of benzophenone and cyclohexane in the zeolite NaX have been analyzed to investigate their proximity, relative mobility, and intermolecular reactivity. Photochemical irradiation of benzophenone in pure cyclohexane yields benzopinacol and benzhydrol as the predominant products. In contrast, irradiation in the solid state leads to 1-cyclohexyl-1,1-diphenylmethanol as the only product by collapse of the radical pair formed after hydrogen abstraction from cyclohexane by excited benzophenone. Phosphorescence analysis at 77 K suggests a highly polar environment, but lack of emission at 300 K in the presence of cyclohexane is assigned to triplet decay via an efficient hydrogen abstraction reaction. Spectral analysis by 13C CPMAS NMR reveals that benzophenone and cyclohexane are adsorbed in an approximate 1:2 ratio. Changes observed in spinning and static samples before and after photolysis are interpreted in terms of molecular motions that are capable of affecting the spectral line width. That benzophenone and cyclohexane share the zeolite supercages in a close packed arrangement was shown by a relatively efficient 1H-13C intermolecular cross polarization from cyclohexane to benzophenone-d10. Comparison of the CPMAS intensities measured with deuterated and nondeuterated benzophenone samples under identical conditions suggest that intermolecular C-D···H-R distances between carbon atoms of deuterated benzophenone and hydrogens of cyclohexane have an average value of ca. 2.2 A?.
- Cizmeciyan, Deniz,Sonnichsen, Laura B.,Garcia-Garibay, Miguel A.
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- Non-Interpenetrated Single-Crystal Covalent Organic Frameworks
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Growth of covalent organic frameworks (COFs) as single crystals is extremely challenging. Inaccessibility of open-structured single-crystal COFs prevents the exploration of structure-oriented applications. Herein we report for the first time a non-interpenetrated single-crystal COF, LZU-306, which possesses the open structure constructed exclusively via covalent assembly. With a high void volume of 80 %, LZU-306 was applied to investigate the intrinsic dynamics of reticulated tetraphenylethylene (TPE) as the individual aggregation-induced-emission moiety. Solid-state 2H NMR investigation has determined that the rotation of benzene rings in TPE, being the freest among the reported cases, is as fast as 1.0×104 Hz at 203 K to 1.5×107 Hz at 293 K. This research not only explores a new paradigm for single-crystal growth of open frameworks, but also provides a unique matrix-isolation platform to reticulate functional moieties into a well-defined and isolated state.
- Han, Jing,Liang, Lin,Luo, Yi,Ma, Tianqiong,Ni, Jianwei,Niu, Jing,Qiu, Yi,Sun, Junliang,Wang, Wei,Wang, Wei David,Wang, Zhi-Peng,Yin, Guan-Lin,Yu, Wei,Zhang, Lei
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supporting information
p. 17991 - 17995
(2020/08/19)
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- Synthesis of indazoles and azaindazoles by intramolecular aerobic oxidative C-N coupling under transition-metal-free conditions
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A transition-metal-free oxidative C-N coupling method has been developed for the synthesis of 1H-azaindazoles and 1H-indazoles from easily accessible hydrazones. The procedure uses TEMPO, a basic additive, and dioxygen gas as the terminal oxidant. This reaction demonstrates better reactivity, functional group tolerance, and broader scope than comparable metal catalyzed reactions. A transition-metal-free oxidative C-N coupling method has been developed for the synthesis of 1H-azaindazoles and 1H-indazoles from easily accessible hydrazones (see scheme). The procedure uses TEMPO, a basic additive, and dioxygen gas as the terminal oxidant. This reaction demonstrates better reactivity, functional group tolerance, and broader scope than comparable metal catalyzed reactions. TEMPO=2,2,6,6-tetramethyl-1-piperidinyloxy.
- Hu, Jiantao,Xu, Huacheng,Nie, Pengju,Xie, Xiaobo,Nie, Zongxiu,Rao, Yu
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supporting information
p. 3932 - 3938
(2014/04/17)
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- Platinum on carbon-catalyzed H-D exchange reaction of aromatic nuclei due to isopropyl alcohol-mediated self- activation of platinum metal in deuterium oxide
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An efficient and simple deuteration method of arenes using the platinum on carbon-isopropyl alcohol-cyclohexane-deuterium oxide combination under hydrogen gas-free conditions was accomplished. Since the hydrogen-deuterium exchange reaction cannot be promoted without isopropyl alcohol, zerovalent platinum metal (on carbon) is self-activated by the in situ-generated very low amount of hydrogen or hydrogen-deuterium gas derived from isopropyl alcohol or isopropyl alcohol-d1. Deuterium-labeled compounds with high deuterium contents can be easily isolated by the filtration of platinum on carbon and simple extraction. The present hydrogen gas-free method is safe from the viewpoint of process chemistry and various arenes possessing a variety of reducible functionalities within the molecule could be effectively and directly deuterium-labeled without undesired reduction. Copyright
- Sawama, Yoshinari,Yamada, Tsuyoshi,Yabe, Yuki,Morita, Kosuke,Shibata, Kyoshiro,Shigetsura, Masahiro,Monguchi, Yasunari,Sajiki, Hironao
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supporting information
p. 1529 - 1534
(2013/06/27)
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- Phenyl ring dynamics in a tetraphenylethylene-bridged metal-organic framework: Implications for the mechanism of aggregation-induced emission
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Molecules that exhibit emission in the solid state, especially those known as aggregation-induced emission (AIE) chromophores, have found applications in areas as varied as light-emitting diodes and biological sensors. Despite numerous studies, the mechanism of fluorescence quenching in AIE chromophores is still not completely understood. To this end, much interest has focused on understanding the low-frequency vibrational dynamics of prototypical systems, such as tetraphenylethylene (TPE), in the hope that such studies would provide more general principles toward the design of new sensors and electronic materials. We hereby show that a perdeuterated TPE-based metal-organic framework (MOF) serves as an excellent platform for studying the low-energy vibrational modes of AIE-type chromophores. In particular, we use solid-state 2H and 13C NMR experiments to investigate the phenyl ring dynamics of TPE cores that are coordinatively trapped inside a MOF and find a phenyl ring flipping energy barrier of 43(6) kJ/mol. DFT calculations are then used to deconvolute the electronic and steric contributions to this flipping barrier. Finally, we couple the NMR and DFT studies with variable-temperature X-ray diffraction experiments to propose that both the ethylenic C' - 'C bond twist and the torsion of the phenyl rings are important for quenching emission in TPE, but that the former may gate the latter. To conclude, we use these findings to propose a set of design criteria for the development of tunable turn-on porous sensors constructed from AIE-type molecules, particularly as applied to the design of new multifunctional MOFs.
- Shustova, Natalia B.,Ong, Ta-Chung,Cozzolino, Anthony F.,Michaelis, Vladimir K.,Griffin, Robert G.,Dinca, Mircea
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p. 15061 - 15070,10
(2020/08/24)
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- Free Energies of Electron Transfer from Ketyls to Isotopically Substituted Ketones
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A series of electron transfer competition reactions between several isotopically different benzophenones was established in liquid ammonia.The resulting electron transfer A(.-) + B = A + B(.-) equilibrium constants were determined via EPR studies and via the physical separation of the anion radical phase from the neutral molecule phase.This anion radical-neutral molecule separation leads to a partial separation of the isotopic isomers involved due to the deviation of the equilibrium constants from unity.Mass spectral analysis of the two phases yields thermodynamic data for the electron transfer that is consistent with the EPR results: when A = benzophenone, Keq at -75 deg C equals 0.52, 0.50, and 0.83 for equilibria involving B = perdeuteriated benzophenone, benzophenone, and benzophenone, respectively.
- Stevenson, Cheryl D.,Halvorsen, Troy D.,Kage, David E.,Reiter, Richard C.,McElheny, Daniel J.
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p. 4634 - 4638
(2007/10/02)
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- AN EFFICIENT SYNTHESIS OF THE ENANTIOMERS OF METHADONE-d10
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A reactions sequence is described to prepare the enantiomers of Methadone-d10.The proposed scheme allows to synthesize racemic Methadone-d10 with 14percent overall yield, starting from benzene-d6. (-)-Methadone-d10 hydrochloride is assigned the (R)- absolute configuration on the basis of its ORD curve.
- Gerardy, B. M.,Poupaert, J.,Dumont, P.
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p. 977 - 980
(2007/10/02)
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- Transformation of Carbinols by RuCl2(PPh3)3 and by Some Other Transition-Metal Catalysts
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Several platinoid metal catalysts have been shown to promote reductive coupling, dehydration, disproportionation, and dehydrogenation of diarylcarbinols.Mechanistic studies were performed at 180-210 deg C with benzhydrol as substrate and RuCl2(PPh3)3 as catalyst.In aromatic hydrocarbon solvents the main process is reductive coupling.In this medium solvated RuCl2(PPh3)2 is suggested to be the active catalyst.In dimethyl sulfoxide the starting complex is transformed initially into RuCl2(PPh3)(Me2SO)2 and causes chiefly carbinol dehydrogenation.Ruthenium alkoxides are implied as common reaction intermediates in all four catalyses.Ruthenium hydrides are suggested to take part in the reductive coupling, disproportionation, and dehydrogenation processes.Some aliphatic and primary aromatic alcohols that do not react by themselves in the presence of RuCl2(PPh3)3 can both serve as active hydrogen donors and form crossover products in the presence of secondary and tertiary aromatic carbinols.
- Pri-Bar, Ilan,Buchman, Ouri,Schumann, Hebert,Kroth, Heinz J.,Blum, Jochanan
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p. 4418 - 4428
(2007/10/02)
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