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101.
In this study, density functional theory (DFT) molecular modeling studies were performed to explore mechanisms underlying the interactions of cocatalysts in Ziegler–Natta olefin polymerization using a range of commercially available cocatalysts, namely, trimethylaluminum (in monomeric and dimeric form, Al2Me6), dimethylaluminum chloride (in monomeric and dimeric form, Al2Me4Cl2), and triisobutylaluminum. In this regard, after exploring structural and electronic features of cocatalysts, by steric maps and conceptual DFT, their interaction with possible impurities in hydrocarbon solvents and monomer feeds such as NH3, CH3OH, H2O, H2S, CO2, and O2 was considered. Then, activation of Ti species, adsorbed on the (110) and (104) surfaces, with the assistance of cocatalysts was studied as well. In this aspect, two possible reactions were investigated: (i) formation of first vacancy on Ti center and (ii) formation of first Ti–C bond by transalkylation reaction with cocatalysts. Finally, the effect of cocatalysts on the stereospecificity of Ti center adsorbed on the (110) surface was also taken into account by DFT calculations. 相似文献
102.
Jesús Antonio Luque-Urrutia Dr. Albert Poater Prof. Dr. Miquel Solà 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(4):804-808
From the analysis of the polarizability of carbon nano-onions (CNOs), it was concluded that CNOs behave as near perfect nanoscopic Faraday cages. If CNOs behave as ideal Faraday cages, the reactivity of the C240 cage should be the same in Li+@C240 and Li+@C60@C240. In this work, the Diels–Alder reaction of cyclopentadiene to the free C240 cage and the C60@C240 CNO together with their Li+-doped counterparts were analyzed using DFT. It was found that in all cases the preferred cycloaddition is on bond [6,6] of type B of C240. Encapsulation of Li+ results in lower enthalpy barriers due to the decrease of the energy of the LUMO orbital of the C240 cage. When the Li+ is placed inside the CNO C60@C240, the decrease in enthalpy barrier is similar to that of Li+@C240. However, the location of Li+ in Li+@C240 (off-centered) and Li+@C60@C240 (centered) is quite different. When Li+ was placed in the center of the C240 cage in Li+@C240, the barriers increased significantly. Taking into account this effect, the barriers in Li+@C240 and Li+@C60@C240 differ by about 4 kcal mol−1. This result can be attributed to the shielding effect of C60 in Li+@C60@C240. As a result, we conclude that this CNO does not act as a perfect Faraday cage. 相似文献
103.
Turias Francesc Solà Miquel Falivene Laura Cavallo Luigi Poater Albert 《Structural chemistry》2016,27(1):409-417
Structural Chemistry - The present computational study complements the recent experimental efforts by Karlin and coworkers to describe the interconversion of nitrite to nitric oxide by means of an... 相似文献
104.
Reaction Mechanism and Regioselectivity of the Bingel–Hirsch Addition of Dimethyl Bromomalonate to La@C2v‐C82 下载免费PDF全文
Juan Pablo Martínez Dr. Marc Garcia‐Borràs Dr. Sílvia Osuna Dr. Jordi Poater Prof. Dr. F. Matthias Bickelhaupt Prof. Dr. Miquel Solà 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(17):5953-5962
We quantum chemically explore the thermodynamics and kinetics of all 65 possible mechanistic pathways of the Bingel–Hirsch addition of dimethyl bromomalonate to the endohedral metallofullerene La@C2v‐C82 that result from the combination of 24 nonequivalent carbon atoms and 35 different bonds present in La@C2v‐C82 by using dispersion‐corrected DFT calculations. Experimentally, this reaction leads to four singly bonded derivatives and one fulleroid adduct. Of these five products, only the singly bonded derivative on C23 could be experimentally identified unambiguously. Our calculations show that La@C2v‐C82 is not particularly regioselective under Bingel–Hirsch conditions. From the obtained results, however, it is possible to make a tentative assignment of the products observed experimentally. We propose that the observed fulleroid adduct results from the attack at bond 19 and that the singly bonded derivatives correspond to the C2, C19, C21, and C23 initial attacks. However, other possibilities cannot be ruled out completely. 相似文献
105.
Dr. Dymytrii Listunov Prof. Ole Hammerich Irving Caballero-Quintana Dr. Albert Poater Cécile Barthes Dr. Carine Duhayon Dr. Mie Højer Larsen Dr. José-Luis Maldonado Dr. Gabriel Ramos-Ortiz Prof. Mogens Brøndsted Nielsen Dr. Valérie Maraval Prof. Remi Chauvin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(47):10707-10711
carbo-Benzene is an aromatic molecule devised by inserting C2 units within each C−C bond of the benzene molecule. By integrating the corresponding carbo-quinoid core as bridging unit in a π-extended tetrathiafulvalene (exTTF), it is shown that a carbo-benzene ring can be reversibly formed by electrochemical reduction or oxidation. The so-called carbo-exTTF molecule was thus experimentally prepared and studied by UV–visible absorption spectroscopy and cyclic voltammetry, as well as by X-ray crystallography and by scanning tunneling microscopy (STM) on a surface of highly oriented pyrolytic graphite (HOPG). The molecule and its oxidized and reduced forms were subjected to a computational study at the density functional theory (DFT) level, supporting carbo-aromaticity as a driving force for the formation of the dication, radical cation, and radical anion. By allowing co-planarity of the dithiolylidene rings and carbo-quinoidal core, carbo-exTTFs present a promising new class of redox-active systems. 相似文献
106.
Dr. Adrián Gómez‐Suárez Dr. Yoshihiro Oonishi Dr. Anthony R. Martin Dr. Sai V. C. Vummaleti Dr. David J. Nelson Dr. David B. Cordes Prof. Alexandra M. Z. Slawin Prof. Dr. Luigi Cavallo Prof. Dr. Steven P. Nolan Dr. Albert Poater 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):1125-1132
Herein, we present a detailed investigation of the mechanistic aspects of the dual gold‐catalysed hydrophenoxylation of alkynes by both experimental and computational methods. The dissociation of [{Au(NHC)}2(μ‐OH)][BF4] is essential to enter the catalytic cycle, and this step is favoured by the presence of bulky, non‐coordinating counter ions. Moreover, in silico studies confirmed that phenol does not only act as a reactant, but also as a co‐catalyst, lowering the energy barriers of several transition states. A gem‐diaurated species might form during the reaction, but this lies deep within a potential energy well, and is likely to be an “off‐cycle” rather than an “in‐cycle” intermediate. 相似文献
107.
Stable Four‐Coordinate Guanidinatosilicon(IV) Complexes with SiN3El Skeletons (El=S,Se, Te) and SiEl Double Bonds 下载免费PDF全文
Felix M. Mück Dorit Kloß Johannes A. Baus Dr. Christian Burschka Dr. Rüdiger Bertermann Dr. Jordi Poater Dr. Célia Fonseca Guerra Prof. Dr. F. Matthias Bickelhaupt Prof. Dr. Reinhold Tacke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):14011-14021
To get information about the reactivity profile of the donor‐stabilized guanidinatosilicon(II) complexes 2 and 3 , a series of oxidative addition reactions was studied. Treatment of 2 and 3 with S8, Se, or Te afforded the respective four‐coordinate silicon(IV ) complexes 8 – 10 and 12 – 14 , which contain an SiN3El skeleton (El=S, Se, Te) with an Si?El double bond. Treatment of 2 with N2O yielded the dinuclear four‐coordinate silicon(IV) complex 11 with an SiN3O skeleton and a central four‐membered Si2O2 ring. Compounds 8 – 14 exist both in the solid state and in solution. They were characterized by elemental analyses, NMR spectroscopic studies in the solid state and in solution, and crystal structure analyses. The reactivity profile of 2 was compared with that of the structurally related bis[N,N′‐diisopropylbenzamidinato(?)]silicon(II) ( 1 ), which is three‐coordinate in the solid state and four‐coordinate in solution ( 1′ ). In contrast, as shown by state‐of‐the‐art relativistic DFT analyses and experimental studies, silylene 2 is three‐coordinate both in the solid state and solution. The three‐coordinate species 2 is 9.3 kcal mol?1 more stable in benzene than the four‐coordinate isomer 2′ . The reason for this was studied by bonding analyses of 2 and 2′ , which were compared with those of 1 and 1′ . The gas‐phase proton affinities of the relevant species in solution ( 1 ′ and 2 ) amount to 288.8 and 273.8 kcal mol?1, respectively. 相似文献
108.
Luan X Mariz R Gatti M Costabile C Poater A Cavallo L Linden A Dorta R 《Journal of the American Chemical Society》2008,130(21):6848-6858
A new class of easily accessible and stable imidazolin-2-ylidenes has been synthesized where the side chains are comprised of substituted naphthyl units. Introduction of the naphthyl groups generates C 2 -symmetric ( rac) and C s- symmetric ( meso) atropisomers, and interconversion between the isomers is studied in detail both experimentally and computationally. Complete characterization of the carbenes includes rare examples of crystallographically characterized saturated NHC structures. Steric properties of the ligands and an investigation of their stability are also presented. In catalysis, the new ligands show versatility comparable to the most widely used NHCs IMes/SIMes or IPr/SIPr. Excellent catalytic results are obtained when either the NHC salts (ring-opening alkylation of epoxides), NHC-modified palladium compounds (C-C and C-N cross-couplings), or NHC-ruthenium complexes (ring-closing metathesis, RCM) are employed. In several cases, this new ligand family provides catalytic systems of higher reactivity than that observed with previously reported NHC compounds. 相似文献
109.
In this work, we explore the geometries, relative stabilities, singlet-triplet (S-T) splittings, and local aromaticities of the 25 possible didehydrophenanthrenes (DDPs) at the BLYP/6-31G(d) level. The main aim is to understand their molecular structure and stability in terms of the electronic structure. To this end, we analyze the changes induced by didehydrogenation in molecular structure and local aromaticity and we investigate the coupling strength between radical centers in DDPs through the evaluation of S-T splittings. Further evidence for the repulsive character of the H-H interactions in phenanthrene's bay region is gained from the relative energies of the triplet states of the different DDPs. 相似文献
110.
Casanovas J Aradilla D Poater J Solà M Estrany F Alemán C 《Physical chemistry chemical physics : PCCP》2012,14(28):10050-10062
The influence of the halogen atom on the intrinsic properties of poly(3-halidethiophene)s has been investigated using experimental and theoretical methodologies. Specifically, the electrochemical, electrical, electronic and morphological properties of poly(3-bromothiophene) have been determined and compared with those recently reported for poly(3-chlorothiophene) [Aradilla et al., Polym. Chem., 2012, 3, 436.]. The electrochemical stability and porosity are smaller for poly(3-bromothiophene) than for poly(3-chlorothiophene) while the π-π* lowest transition energy is higher for the former than for the latter. Moreover, quantum mechanical calculations on model oligomers have evidenced that the conformational properties of poly(3-halidethiophene)s, where the halogen is fluorine, chloride or bromine, are dominated by steric interactions and, therefore, are significantly influenced by the size of the halogen atoms. Both the ionization potential and the π-π* lowest transition energy have been predicted to increase slightly when the π-donor character of the halogen atom decreases, in agreement with experimental observations. 相似文献