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1.
Dr. Jordan Donat Mr. Patrick Dubourdeaux Dr. Martin Clémancey Dr. Julia Rendon Clara Gervasoni Mr. Morgan Barbier Jessica Barilone Dr. Jacques Pécaut Prof. Dr. Serge Gambarelli Prof. Dr. Pascale Maldivi Prof. Dr. Jean-Marc Latour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202201875
Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from FeII and FeIII precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV-visible, Mössbauer), ESI-MS and DFT studies, an FeIV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the FeII precursor was expected by a two-electron oxidative addition, its formation from an FeIII precursor was unprecedented. Thanks to a combination of spectroscopic (UV-visible, EPR, Hyscore and Mössbauer), ESI-MS and DFT studies, we found that, when starting from the FeIII precursor, an FeIII tosyliodinane adduct was formed and decomposed into an FeV tosylimido species which generated the catalytically active FeIV tosylimide through a comproportionation process with the FeIII precursor. 相似文献
2.
Saqib Kamal Arif I. Inamdar Kuan-Ru Chiou Batjargal Sainbileg Muhammad Usman Jenq-Wei Chen Tzuoo-Tsair Luo Michitoshi Hayashi Chen-Hsiung Hung Wen-Feng Liaw Kuang-Lieh Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(30):e202103905
The dielectric properties of coordination polymers has been a topic of recent interest, but the role of different functional groups on the dielectric properties of these polymers has not yet been fully addressed. Herein, the effects of electron-donating (R=NH2) and electron-withdrawing (R=NO2) groups on the dielectric behavior of such materials were investigated for two thermally stable and guest-free Zn-based coordination polymers, [Zn(L1)(L2)]n ( 1 ) and [Zn(L1)(L3)]n ( 2 ) [L1=2-(2-pyridyl) benzimidazole (Pbim), L2=5-aminoisophthalate (Aip), and L3=5-nitroisophthalate (Nip)]. The results of dielectric studies of 1 revealed that it possesses a high dielectric constant (κ=65.5 at 1 kHz), while compound 2 displayed an even higher dielectric constant (κ=110.3 at 1 kHz). The electron donating and withdrawing effects of the NH2 and NO2 substituents induce changes in the polarity of the polymers, which is due to the inductive effect from the aryl ring for both NO2 and NH2. Theoretical results from density functional theory (DFT) calculations, which also support the experimental findings, show that both compounds have a distinct electronic behavior with diverse wide bandgaps. The significance of the current work is to provide information about the structure-dielectric property relationships. So, this study promises to pave the way for further research on the effects of different functional groups on coordination polymers on their dielectric properties. 相似文献
3.
This paper is concerned with the Cauchy problem on the Boltzmann equation without angular cutoff assumption for hard potential in the whole space. When the initial data is a small perturbation of a global Maxwellian, the global existence of solution to this problem is proved in unweighted Sobolev spaces with . But if we want to obtain the optimal temporal decay estimates, we need to add the velocity weight function, in this case the global existence and the optimal temporal decay estimate of the Boltzmann equation are all established. Meanwhile, we further gain a more accurate energy estimate, which can guarantee the validity of the assumption in Chen et al. (0000). 相似文献
4.
Edward G. Sheetz Zhao Zhang Alyssa Marogil Minwei Che Dr. Maren Pink Dr. Veronica Carta Prof. Dr. Krishnan Raghavachari Prof. Dr. Amar H. Flood 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201584
The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF3−). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF3−, by cyanostar macrocycles that are size-complementary to the inorganic BF4− progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R−BF3− anions. 相似文献
5.
Tomoyuki Nakatsuka 《Mathematische Nachrichten》2021,294(1):98-117
We study the existence of a time‐periodic solution with pointwise decay properties to the Navier–Stokes equation in the whole space. We show that if the time‐periodic external force is sufficiently small in an appropriate sense, then there exists a time‐periodic solution of the Navier–Stokes equation such that and uniformly in as . Our solution decays faster than the time‐periodic Stokes fundamental solution and the faster decay of its spatial derivatives of higher order is also described. 相似文献
6.
We investigate the possibility of phantom crossing in the dark energy sector and the solution for the Hubble tension between early and late universe observations. We use robust combinations of different cosmological observations, namely the Cosmic Microwave Background (CMB), local measurement of Hubble constant (), Baryon Acoustic Oscillation (BAO) and SnIa for this purpose. For a combination of CMB+BAO data that is related to early universe physics, phantom crossing in the dark energy sector was confirmed at a 95% confidence level and we obtained the constraint km/s/Mpc at a 68% confidence level, which is in perfect agreement with the local measurement by Riess et al. We show that constraints from different combinations of data are consistent with each other and all of them are consistent with phantom crossing in the dark energy sector. For the combination of all data considered, we obtained the constraint km/s/Mpc at a 68% confidence level and the phantom crossing happening at the scale factor at a 68% confidence level. 相似文献
7.
Dr. Manussada Ratanasak Takumi Murata Taishin Adachi Prof. Jun-ya Hasegawa Prof. Tadashi Ema 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(58):e202202210
BPh3 catalyzes the N-methylation of secondary amines and the C-methylenation (methylene-bridge formation between aromatic rings) of N,N-dimethylanilines or 1-methylindoles in the presence of CO2 and PhSiH3; these reactions proceed at 30–40 °C under solvent-free conditions. In contrast, B(C6F5)3 shows little or no activity. 11B NMR spectra suggested the generation of [HBPh3]−. The detailed mechanism of the BPh3-catalyzed N-methylation of N-methylaniline ( 1 ) with CO2 and PhSiH3 was studied by using DFT calculations. BPh3 promotes the conversion of two substrates (N-methylaniline and CO2) into a zwitterionic carbamate to give three-component species [Ph(Me)(H)N+CO2−⋅⋅⋅BPh3]. The carbamate and BPh3 act as the nucleophile and Lewis acid, respectively, for the activation of PhSiH3 to generate [HBPh3]−, which is used to produce key CO2-derived species, such as silyl formate and bis(silyl)acetal, essential for the N-methylation of 1 . DFT calculations also suggested other mechanisms involving water for the generation of [HBPh3]− species. 相似文献
8.
Corinne Rondeau-Mouro Mireille Cambert Laurent Blondel Yves Diascorn Léo Mbaya Nor Nadiah Binti Ahmad Nazari Sarah Helary Tiphaine Lucas 《Magnetic resonance in chemistry : MRC》2022,60(7):678-691
A temperature control unit was implemented to vary the temperature of samples studied on a commercial Mobile Universal Surface Explorer nuclear magnetic resonance (MOUSE-NMR) apparatus. The device was miniaturized to fit the maximum MOUSE sampling depth (25 mm). It was constituted by a sample holder sandwiched between two heat exchangers placed below and above the sample. Air was chosen as the fluid to control the temperature at the bottom of the sample, at the interface between the NMR probe and the sample holder, in order to gain space. The upper surface of the sample was regulated by the circulation of water inside a second heat exchanger placed above the sample holder. The feasibility of using such a device was demonstrated first on pure water and then on several samples of bread dough with different water contents. For this, T1 relaxation times were measured at various temperatures and depths and were then compared with those acquired with a conventional compact closed-magnet spectrometer. Discussion of results was based on biochemical transformations in bread dough (starch gelatinization and gluten heat denaturation). It was demonstrated that, within a certain water level range, and because of the low magnetic field strength of the MOUSE, a linear relationship could be established between T1 relaxation times and the local temperature in the dough sample. 相似文献
9.
10.
Weiyi Li Geng Leng Caiqin Li Yajing Lyu 《International journal of quantum chemistry》2020,120(8):e26150
The mechanisms of CO2 coupling with the propargylic alcohol using alkali carbonates M2CO3 (M = Li, Na, K, Cs) have been investigated by means of density functional theory calculations. The calculations reveal that the target product tetronic acid (TA) is yielded through two stages: (a) the formation of the α-alkylidene cyclic carbonate (αACC) intermediate via Cs2CO3-mediated carboxylative cyclization of the propargylic alcohol with CO2, and (b) the conversion of the αACC intermediate with Cs2CO3 to produce the cesium salt of the TA. Since the overall kinetic barriers for the two stages are comparable and affordable, the excellent chemoselectivity to the TA should be primarily originated from the high thermodynamic stability of the cesium salt of the TA. Moreover, relative to the TA, the possibility to yield the by-product acyclic carbonate can be excluded due to the both kinetics and thermodynamic inferiority. This result is different from the organic base-mediated reaction. Alternatively, our calculations predict that CsHCO3 together generated with the cesium salt of the TA might also be an available mediating reagent for the incorporation of CO2 with the propargylic alcohol. Compared to other alkali carbonates M2CO3 (M = Li, Na, K), the stronger basicity of Cs2CO3 and the lower ionic potential of cesium ion can raise the effective concentration of the αACC intermediate, and thus the conversion of the αACC intermediate into the cesium salt of the TA can be achieved with high yield. 相似文献