共查询到20条相似文献,搜索用时 15 毫秒
1.
Dr. Francisco Núñez‐Zarur Dr. Xavier Solans‐Monfort Prof. Roser Pleixats Dr. Luis Rodríguez‐Santiago Prof. Mariona Sodupe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(43):14553-14565
DFT (B3LYP‐D) calculations have been used to better understand the origin of the recovered Hoveyda–Grubbs derivative catalysts after ring‐closing diene or enyne metathesis reactions. For that, we have considered the activation process of five different Hoveyda–Grubbs precursors in the reaction with models of usual diene and enyne reactants as well as the potential precursor regeneration through the release/return mechanism. The results show that, regardless of the nature of the initial precursor, the activation process needs to overcome relatively high energy barriers, which is in agreement with a relatively slow process. The precursor regeneration process is in all cases exergonic and it presents low energy barriers, particularly when compared to those of the activation process. This indicates that the precursor regeneration should always be feasible, unlike the moderate recoveries sometimes observed experimentally, which suggests that other competitive processes that hinder recovery should take place. Indeed, calculations presented in this work show that the reactions between the more abundant olefinic products and the active carbenes usually require lower energy barriers than those that regenerate the initial precatalyst, which could prevent precursor regeneration. On the other hand, varying the precursor concentration with time obtained from the computed energy barriers shows that, under the reaction conditions, the precursor activation is incomplete, thereby suggesting that the origin of the recovered catalyst probably arises from incomplete precursor activation. 相似文献
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Juan Pablo Martínez Dr. Sai Vikrama Chaitanya Vummaleti Dr. Laura Falivene Prof. Dr. Steven P. Nolan Prof. Dr. Luigi Cavallo Prof. Dr. Miquel Solà Dr. Albert Poater 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(19):6617-6623
Density functional theory calculations have been used to explore the potential of Ru‐based complexes with 1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene (SIMes) ligand backbone ( A ) being modified in silico by the insertion of a C60 molecule ( B and C ), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A , B , and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron‐withdrawing N‐heterocyclic carbene improves the performance of unannulated complex A . The efficiency of complex B is only surpassed by complex A when the backbone of the N‐heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic‐donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A . Overall, this study indicates that such Ru‐based complexes B and C might have the potential to be effective olefin metathesis catalysts. 相似文献
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Competition Between π–π and CH/π Interactions: A Comparison of the Structural and Electronic Properties of Alkoxy‐Substituted 1,8‐Bis((propyloxyphenyl)ethynyl)naphthalenes 下载免费PDF全文
Dr. Bradley E. Carson Trent M. Parker Dr. Edward G. Hohenstein Dr. Glen L. Brizius Whitney Komorner Prof. Rollin A. King Prof. David M. Collard Prof. C. David Sherrill 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(52):19168-19175
The structural and electronic consequences of π–π and C?H/π interactions in two alkoxy‐substituted 1,8‐bis‐ ((propyloxyphenyl)ethynyl)naphthalenes are explored by using X‐ray crystallography and electronic structure computations. The crystal structure of analogue 4 , bearing an alkoxy side chain in the 4‐position of each of the phenyl rings, adopts a π‐stacked geometry, whereas analogue 8 , bearing alkoxy groups at both the 2‐ and the 5‐positions of each ring, has a geometry in which the rings are splayed away from a π‐stacked arrangement. Symmetry‐adapted perturbation theory analysis was performed on the two analogues to evaluate the interactions between the phenylethynyl arms in each molecule in terms of electrostatic, steric, polarization, and London dispersion components. The computations support the expectation that the π‐stacked geometry of the alkoxyphenyl units in 4 is simply a consequence of maximizing π–π interactions. However, the splayed geometry of 8 results from a more subtle competition between different noncovalent interactions: this geometry provides a favorable anti‐alignment of C?O bond dipoles, and two C?H/π interactions in which hydrogen atoms of the alkyl side chains interact favorably with the π electrons of the other phenyl ring. These favorable interactions overcome competing π–π interactions to give rise to a geometry in which the phenylethynyl substituents are in an offset, unstacked arrangement. 相似文献
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Dr. Junjian Miao Prof. Bo Song Prof. Yi Gao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(8):2586-2589
The interaction between a noble gas atom and an aromatic π‐electron system, which mainly originates from the London dispersion force, is very weak and has not attracted enough attention yet. Herein, we reported a type of notably enhanced aerogen–π interaction between cation–π systems and noble gas atoms. The binding strength of a divalent cation–π system with a xenon atom is comparable to a moderate hydrogen bond (up to ca. 7 kcal mol?1), whereas krypton and argon atoms produce slightly weaker interactions. Energy‐decomposition analysis reveals that the induction interaction is responsible for the stabilization of divalent cation–π?Xe species besides the dispersion interaction. Our results might be helpful to increase the understanding of some unsolved mysteries of aerogens. 相似文献
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Tracey M. McLean Deidre M. Cleland Samuel J. Lind Keith C. Gordon Prof. Shane G. Telfer Dr. Mark R. Waterland Dr. 《化学:亚洲杂志》2010,5(9):2036-2046
A recently reported new class of ruthenium complexes containing 2,2′‐bipyridine and a dipyrrin ligand in the coordination sphere exhibit both strong metal‐to‐ligand charge‐transfer (MLCT) and π–π* transitions. Quantitative analysis of the resonance Raman scattering intensities and absorption spectra reveals only weak electronic interactions between these states despite direct coordination of the bipyridyl and dipyrrin ligands to the central ruthenium atom. On the basis of DFT calculations and time‐dependent DFT (TD‐DFT), we propose that the electronic excited states closely resemble “pure” MLCT and π–π* states. Resonance Raman intensity analysis demonstrates that a large amplitude transannular torsional motion provides a mechanism for relaxation on the π–π* excited‐state surface. We assert that this result is generally applicable to a range of dipyrrin complexes such as boron–dipyrrin and metallodipyrrin systems. Despite the large torsional distortion between the phenyl ring and the dipyrromethene plane, π–π* excitation extends out onto the phenyl ring which may have important consequences in solar‐energy‐conversion applications of ruthenium–dipyrrin complexes. 相似文献
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《Chemphyschem》2003,4(12):1344-1348
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Dr. Alessandra Forni Dr. Stefano Pieraccini Dr. Stefano Rendine Dr. Fabio Gabas Prof. Dr. Maurizio Sironi 《Chemphyschem》2012,13(18):4224-4234
Halogen bonding is a noncovalent interaction between a halogen atom and a nucleophilic site. Interactions involving the π electrons of aromatic rings have received, up to now, little attention, despite the large number of systems in which they are present. We report binding energies of the interaction between either NCX or PhX (X=F, Cl, Br, I) and the aromatic benzene system as determined with the coupled cluster with perturbative triple excitations method [CCSD(T)] extrapolated at the complete basis set limit. Results are compared with those obtained by Møller–Plesset perturbation theory to second order (MP2) and density functional theory (DFT) calculations by using some of the most common functionals. Results show the important role of DFT in studying this interaction. 相似文献
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Understanding the Fundamental Role of π/π, σ/σ, and σ/π Dispersion Interactions in Shaping Carbon‐Based Materials 下载免费PDF全文
Dr. Mercedes Alonso Tatiana Woller Dr. Francisco J. Martín‐Martínez Dr. Julia Contreras‐García Prof. Paul Geerlings Prof. Frank De Proft 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4931-4941
Noncovalent interactions involving aromatic rings, such as π‐stacking and CH/π interactions, are central to many areas of modern chemistry. However, recent studies proved that aromaticity is not required for stacking interactions, since similar interaction energies were computed for several aromatic and aliphatic dimers. Herein, the nature and origin of π/π, σ/σ, and σ/π dispersion interactions has been investigated by using dispersion‐corrected density functional theory, energy decomposition analysis, and the recently developed noncovalent interaction (NCI) method. Our analysis shows that π/π and σ/σ stacking interactions are equally important for the benzene and cyclohexane dimers, explaining why both compounds have similar boiling points. Also, similar dispersion forces are found in the benzene???methane and cyclohexane???methane complexes. However, for systems larger than naphthalene, there are enhanced stacking interactions in the aromatic dimers adopting a parallel‐displaced configuration compared to the analogous saturated systems. Although dispersion plays a decisive role in stabilizing all the complexes, the origin of the π/π, σ/σ, and σ/π interactions is different. The NCI method reveals that the dispersion interactions between the hydrogen atoms are responsible for the surprisingly strong aliphatic interactions. Moreover, whereas σ/σ and σ/π interactions are local, the π/π stacking are inherently delocalized, which give rise to a non‐additive effect. These new types of dispersion interactions between saturated groups can be exploited in the rational design of novel carbon materials. 相似文献
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The Challenge of Linear (E)‐Enones in the Rh‐Catalyzed,Asymmetric 1,4‐Addition Reaction of Phenylboronic Acid: A DFT Computational Analysis 下载免费PDF全文
Prof. Hua‐Li Qin Xiao‐Qing Chen Zhen‐Peng Shang Prof. Eric Assen B. Kantchev 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):3079-3086
Why are linear (E)‐enones such challenging substrates in the Rh‐catalyzed asymmetric arylation with boronic acids, which is one of the most important asymmetric catalysis methods? DFT computations show that these substrates adopt a specific conformation in which the largest substituent is antiperiplanar to RhI π‐complexed with the C?C bond within the enantioselectivity‐determining carborhodation transition state. Additionally, for such structures, there is a strong, but not exclusive, preference for s‐cis enone conformation. This folding minimizes steric interactions between the substrate and the ligand, and hence reduces the enantioselectivity. This idea is further confirmed by investigating three computation‐only substrate “probes”, one of which is capable of double asymmetric induction, and a recent computationally designed 1,5‐diene ligand. On average, excellent agreement between predicted and experimental enantioselectivity was attained by a three‐pronged approach: 1) thorough conformational search within ligand and substrate subunits to locate the most preferred carborhodation transition state; 2) including dispersion interaction and long‐range corrections by SMD/ωB97xD/DGDZVP level of theory; and 3) full substrate and ligand modeling. Based on the results, a theory‐enhanced enantioselectivity model that is applicable to both chiral diene and diphosphane ligands is proposed. 相似文献
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Uncovering Intramolecular π‐Type Hydrogen Bonds in Solution by NMR Spectroscopy and DFT Calculations
Prof. Dr. Piero Mastrorilli Prof. Vito Gallo Dr. Stefano Todisco Prof. Mario Latronico Dr. Giacomo Saielli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(23):7964-7969
Reaction between the phosphinito bridged diplatinum species [(PHCy2)Pt(μ‐PCy2){κ2P,O‐μ‐P(O)Cy2}Pt(PHCy2)](Pt–Pt) ( 1 ), and (trimethylsilyl)acetylene at 273 K affords the σ‐acetylide complex [(PHCy2)(η1‐Me3SiC≡C)Pt(μ‐PCy2)Pt(PHCy2){κP‐P(OH)Cy2}](Pt–Pt) ( 2 ) featuring an intramolecular π‐type hydrogen bond. Scalar and dipolar couplings involving the POH proton were detected by 2D NMR experiments. Relativistic DFT calculations of the geometry, relative energy, and NMR properties of model systems of 2 confirmed the structural assignment and allowed the energy of the π‐type hydrogen bond to be estimated (ca. 22 kJ mol?1). 相似文献
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Orbital Effect‐Induced Anomalous Anion–π Interactions between Electron‐Rich Aromatic Hydrocarbons and Fluoride 下载免费PDF全文
Dr. Guosheng Shi Jinrong Yang Prof. Yihong Ding Prof. Haiping Fang 《Chemphyschem》2014,15(12):2588-2594
Anion–π interactions generally exist between an anion and an electron‐deficient π‐ring because of the electron‐accepting character of the ring. In this paper, we report orbital effect‐induced anomalous binding between electron‐rich π systems and F? through anion–π interactions calculated at the MP2/6‐31+G(d,p) and ωB97X‐D/6‐31+G(d,p) levels of theory. We find that anion–π interactions between F? and electron‐rich π rings increase markedly with increasing number of π electrons and size of the π rings. This is contrary to intuition because anion–π interactions would be expected to gradually decrease because of gradually increasing Coulombic repulsion between the negative charge of the anions and gradually increasing number of π electrons of the aromatic surfaces. Energy decomposition analysis showed that the key to this anomalous effect is the more effective delocalization of negative charge to the unoccupied π* orbitals of larger π rings, which is termed an “orbital effect”. 相似文献
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Cover Picture: Understanding the Fundamental Role of π/π, σ/σ, and σ/π Dispersion Interactions in Shaping Carbon‐Based Materials (Chem. Eur. J. 17/2014) 下载免费PDF全文
Dr. Mercedes Alonso Tatiana Woller Dr. Francisco J. Martín‐Martínez Dr. Julia Contreras‐García Prof. Paul Geerlings Prof. Frank De Proft 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4841-4841
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Amit Das Dipl.‐Chem. Thomas Michael Scherer Prasenjit Mondal Dr. Shaikh M. Mobin Prof. Dr. Wolfgang Kaim Prof. Dr. Goutam Kumar Lahiri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(45):14434-14443
New compounds [Ru(pap)2(L)](ClO4), [Ru(pap)(L)2], and [Ru(acac)2(L)] (pap=2‐phenylazopyridine, L?=9‐oxidophenalenone, acac?=2,4‐pentanedionate) have been prepared and studied regarding their electron‐transfer behavior, both experimentally and by using DFT calculations. [Ru(pap)2(L)](ClO4) and [Ru(acac)2(L)] were characterized by crystal‐structure analysis. Spectroelectrochemistry (EPR, UV/Vis/NIR), in conjunction with cyclic voltammetry, showed a wide range of about 2 V for the potential of the RuIII/II couple, which was in agreement with the very different characteristics of the strongly π‐accepting pap ligand and the σ‐donating acac? ligand. At the rather high potential of +1.35 V versus SCE, the oxidation of L? into L. could be deduced from the near‐IR absorption of [RuIII(pap)(L.)(L?)]2+. Other intense long‐wavelength transitions, including LMCT (L?→RuIII) and LL/CT (pap.?→L?) processes, were confirmed by TD‐DFT results. DFT calculations and EPR data for the paramagnetic intermediates allowed us to assess the spin densities, which revealed two cases with considerable contributions from L‐radical‐involving forms, that is, [RuIII(pap0)2(L?)]2+?[RuII(pap0)2(L.)]2+ and [RuIII(pap0)(L?)2]+?[RuII(pap0)(L?)(L?)]+. Calculations of electrogenerated complex [RuII(pap.?)(pap0)(L?)] displayed considerable negative spin density (?0.188) at the bridging metal. 相似文献
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A Dinuclear Ruthenium‐Based Water Oxidation Catalyst: Use of Non‐Innocent Ligand Frameworks for Promoting Multi‐Electron Reactions 下载免费PDF全文
Tanja M. Laine Dr. Markus D. Kärkäs Prof. Dr. Rong‐Zhen Liao Prof. Per E. M. Siegbahn Prof. Björn Åkermark 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(28):10039-10048
Insight into how H2O is oxidized to O2 is envisioned to facilitate the rational design of artificial water oxidation catalysts, which is a vital component in solar‐to‐fuel conversion schemes. Herein, we report on the mechanistic features associated with a dinuclear Ru‐based water oxidation catalyst. The catalytic action of the designed Ru complex was studied by the combined use of high‐resolution mass spectrometry, electrochemistry, and quantum chemical calculations. Based on the obtained results, it is suggested that the designed ligand scaffold in Ru complex 1 has a non‐innocent behavior, in which metal–ligand cooperation is an important part during the four‐electron oxidation of H2O. This feature is vital for the observed catalytic efficiency and highlights that the preparation of catalysts housing non‐innocent molecular frameworks could be a general strategy for accessing efficient catalysts for activation of H2O. 相似文献
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Dr. Jean‐Pierre Djukic Wissam Iali Dr. Michel Pfeffer Dr. Xavier‐Frédéric Le Goff 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(19):6063-6078
Facial selectivity during the π‐coordination of pseudo‐tetrahedral iridacycles by neutral (Cr(CO)3), monocationic (Cp*Ru+), and biscationic (Cp*Ir2+) metal centers was directly influenced by the coulombic imbalance in the coordination sphere of the chelated Ir center. We also showed by using theoretical calculations that the feasibility of the related metallacycles that displayed metallocenic planar chirality was dependent to the presence of an electron‐donating group, such as NMe2, which contributed to the overall stability of the complexes. When the π‐bonded moiety was the strongly electron‐withdrawing Cp*Ir2+ group, the electron donation from NMe2 resulted in major conformational changes, with a barrier to rotation of about 17 kcal mol?1 for this group that became spectroscopically diastereotopic (high‐field 1H NMR spectroscopy). This peculiar property is proposed as a means to introduce a new type of constitutional chirality at the nitrogen center: planar chirality at tertiary aromatic amines. 相似文献
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The π‐Back‐Bonding Modulation and Its Impact in the Electronic Properties of CuII Antineoplastic Compounds: An Experimental and Theoretical Study 下载免费PDF全文
Juan Carlos García‐Ramos Dr. Rodrigo Galindo‐Murillo Araceli Tovar‐Tovar Ana Luisa Alonso‐Saenz Virginia Gómez‐Vidales Dr. Marcos Flores‐Álamo Dr. Luis Ortiz‐Frade Dr. Fernando Cortes‐Guzmán Dr. Rafael Moreno‐Esparza Prof. Antonio Campero Prof. Lena Ruiz‐Azuara 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13730-13741