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971.
采用密度泛函理论计算方法模拟了简单钴卟啉过氧中间体PCo-O2与环己烷C6H12的作用,分析了反应路径中各驻点能量和反应过渡态分子构型。研究结果表明,PCo-O2向底物环己烷夺氢的反应可以延正方向进行,二线态PCo-O2更具反应活性,反应过程中Co-O键得到加强,O-O键被削弱。依据理论计算结果,探讨了四苯基钴卟啉催化环己烷氧化生成环己醇和环己酮的反应机理,指出反应延Lyons高价金属氧代物机理生成环己醇,而反应循环中产生的烷基自由基可以延烷基过氧化过渡金属配合物反应机理进行生成环己酮。 相似文献
972.
The structural, elastic, mechanical, electronic, optical properties and effective masses of CuMIIIBO2 (MIIIB = Sc, Y, La) compounds have been investigated by the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory under local density approximation. The equilibrium structural parameters are in good agreement with previous experimental and theoretical data. To our knowledge, there are no available data of elastic constants for comparison. The bulk, shear and Young's modulus, ratio of B/G, Poisson's ratio and Lamé's constants of CuMIIIBO2 have been studied. The electronic structures of CuMIIIBO2 are consistent with other calculations. The population analysis, charge densities and effective masses have been shown and analyzed. The imaginary and real parts of the dielectric function, refractive index and extinction coefficient of CuMIIIBO2 are calculated. The interband transitions to absorption of CuMIIIBO2 have been analyzed. 相似文献
973.
Two States Are Not Enough: Quantitative Evaluation of the Valence‐Bond Intramolecular Charge‐Transfer Model and Its Use in Predicting Bond Length Alternation Effects
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Dr. Peter D. Jarowski Prof. Yirong Mo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(51):17214-17221
The structural weights of the canonical resonance contributors used in the Two‐state valence‐bond charge‐transfer model, neutral (N, R1) and ionic (VB‐CT, R2), to the ground states and excited states of a series of linear dipolar intramolecular charge‐transfer chromophores containing a buta‐1,3‐dien‐1,4‐diyl bridge have been computed by using the block‐localized wavefunction (BLW) method at the B3LYP/6‐311+G(d) level to provide the first quantitative assessment of this simple model. Ground‐ and excited‐state analysis reveals surprisingly low ground‐state structural weights for the VB‐CT resonance form using either this Two‐state model or an expanded Ten‐state model. The VB‐CT state is found to be more prominent in the excited state. Individual resonance forms were structurally optimized to understand the origins of the bond length alternation (BLA) of the bridging unit. Using a Wheland energy‐based weighting scheme, the weighted average of the optimized bond lengths with the Two‐state model was unable to reproduce the BLA features with values 0.04 to 0.02 Å too large compared to the fully delocalized (FD) structure (BLW: ca. ?0.13 to ?0.07 Å, FD: ca. ?0.09 to ?0.05 Å). Instead, an expanded Ten‐state model fit the BLA values of the FD structure to within only 0.001 Å of FD. 相似文献
974.
Inside Cover: New Concepts for Designing d10‐M(L)n Catalysts: d Regime,s Regime and Intrinsic Bite‐Angle Flexibility (Chem. Eur. J. 36/2014)
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975.
Hye Mi Oh Ji Eun Park Jisu Kim Ju Hyun Kim Prof. Youn K. Kang Prof. Young Keun Chung 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(29):9024-9036
A method for the synthesis of bicyclo[4.1.0]heptenes from 1,6‐enynes through Pd‐catalyzed cycloisomerization has been developed. N‐ and O‐tethered 1,6‐enynes were successfully transformed to their corresponding 3‐aza‐ and 3‐oxabicyclo[4.1.0]heptenes in reasonable‐to‐high yields using the catalysts [PdCl2(CH3CN)2]/P(OPh)3 or [Pd(maleimidate)2(PPh3)2] in toluene. The computational calculations using density functional theory indicate that [PdCl2{P(OPh)3}] in the oxidation state PdII acts as the active catalyst species for the formation of 3‐azabicyclo[4.1.0]heptenes through 6‐endo‐dig cyclization. 相似文献
976.
A Valence Bond Model for Electron‐Rich Hypervalent Species: Application to SFn (n=1, 2, 4), PF5, and ClF3
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Dr. Benoit Braida Tristan Ribeyre Prof. Philippe C. Hiberty 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9643-9649
Some typical hypervalent molecules, SF4, PF5, and ClF3, as well as precursors SF (4Σ? state) and SF2 (3B1 state), are studied by means of the breathing‐orbital valence bond (BOVB) method, chosen for its capability of combining compactness with accuracy of energetics. A unique feature of this study is that for the first time, the method used to gain insight into the bonding modes is the same as that used to calculate the bonding energies, so as to guarantee that the qualitative picture obtained captures the essential physics of the bonding system. The 4Σ? state of SF is shown to be bonded by a three‐electron σ bond assisted by strong π back‐donation of dynamic nature. The linear 3B1 state of SF2, as well as the ground states of SF4, PF5 and ClF3, are described in terms of four VB structures that all have significant weights in the range 0.17–0.31, with exceptionally large resonance energies arising from their mixing. It is concluded that the bonding mode of these hypervalent species and isoelectronic ones complies with Coulson’s version of the Rundle–Pimentel model, but assisted by charge‐shift bonding. The conditions for hypervalence to occur are stated. 相似文献
977.
Tuning the Electronic Coupling in Cyclometalated Diruthenium Complexes through Substituent Effects: A Correlation between the Experimental and Calculated Results
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Jiang‐Yang Shao Prof. Dr. Yu‐Wu Zhong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(28):8702-8713
A common bridging ligand, 3,3′,5,5′‐tetrakis(N‐methylbenzimidazol‐2‐yl)biphenyl, and four terpyridine terminal ligands with various substituents (amine, tolyl, nitro, and ester groups) have been used to synthesize ten cyclometalated diruthenium complexes 1 2+– 10 2+. Among them, compounds 1 2+– 6 2+ are redox nonsymmetric, and others are symmetric. These complexes show two RuIII/II processes and an intervalence charge transfer (IVCT) transition in the one‐electron oxidized state. The potential separation (ΔE) of 1 2+– 10 2+ has been correlated to the energy difference ΔG0, the energy of the IVCT band Eop, and the ground‐state delocalization coefficient α2. Time‐dependent (TD)DFT calculations suggest that the absorptions in the visible region of 1 2+– 6 2+ are mainly associated with the metal‐to‐ligand charge‐transfer transitions from both ruthenium ions and to both terminal ligands and the bridging ligand. However, the energies of these transitions vary significantly. DFT calculations have been performed on 1 2+– 6 2+ and 1 3+– 6 3+ to give information on the electronic structures and spin populations of the mixed‐valent compounds. The TDDFT‐predicted IVCT excitations reproduce well the experimental trends in transition energies. In addition, three monoruthenium complexes have been synthesized for a comparison study. 相似文献
978.
Dipl.‐Chem. Alexander Rupp Dr. Nataliya Roznyatovskaya Dr. Harald Scherer Dr. Witali Beichel Petra Klose Carola Sturm Dr. Anke Hoffmann Dr. Jens Tübke Prof. Dr. Thorsten Koslowski Prof. Dr. Ingo Krossing 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9794-9804
Several, partly new, ionic liquids (ILs) containing imidazolium and ammonium cations as well as the medium‐sized [NTf2]? (0.230 nm3; Tf=CF3SO3?) and the large [Al(hfip)4]? (0.581 nm3; hfip=OC(H)(CF3)2) anions were synthesized and characterized. Their temperature‐dependent viscosities and conductivities between 25 and 80 °C showed typical Vogel–Fulcher–Tammann (VFT) behavior. Ion‐specific self‐diffusion constants were measured at room temperature by pulsed‐gradient stimulated‐echo (PGSTE) NMR experiments. In general, self‐diffusion constants of both cations and anions in [Al(hfip)4]?‐based ILs were higher than in [NTf2]?‐based ILs. Ionicities were calculated from self‐diffusion constants and measured bulk conductivities, and showed that [Al(hfip)4]?‐based ILs yield higher ionicities than their [NTf2]? analogues, the former of which reach values of virtually 100 % in some cases.From these observations it was concluded that [Al(hfip)4]?‐based ILs come close to systems without any interactions, and this hypothesis is underlined with a Hirshfeld analysis. Additionally, a robust, modified Marcus theory quantitatively accounted for the differences between the two anions and yielded a minimum of the activation energy for ion movement at an anion diameter of slightly greater than 1 nm, which fits almost perfectly the size of [Al(hfip)4]?. Shallow Coulomb potential wells are responsible for the high mobility of ILs with such anions. 相似文献
979.
Johannes Hoja Prof. Dr. Alexander F. Sax Prof. Dr. Krzysztof Szalewicz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(8):2292-2300
The stability and geometry of a hydrogen‐bonded dimer is traditionally attributed mainly to the central moiety A?H???B, and is often discussed only in terms of electrostatic interactions. The influence of substituents and of interactions other than electrostatic ones on the stability and geometry of hydrogen‐bonded complexes has seldom been addressed. An analysis of the interaction energy in the water dimer and several alcohol dimers—performed in the present work by using symmetry‐adapted perturbation theory—shows that the size and shape of substituents strongly influence the stabilization of hydrogen‐bonded complexes. The larger and bulkier the substituents are, the more important the attractive dispersion interaction is, which eventually becomes of the same magnitude as the total stabilization energy. Electrostatics alone are a poor predictor of the hydrogen‐bond stability trends in the sequence of dimers investigated, and in fact, dispersion interactions predict these trends better. 相似文献
980.
New Concepts for Designing d10‐M(L)n Catalysts: d Regime,s Regime and Intrinsic Bite‐Angle Flexibility
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Lando P. Wolters Dr. Willem‐Jan van Zeist Prof. Dr. F. Matthias Bickelhaupt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(36):11370-11381
Our aim is to understand the electronic and steric factors that determine the activity and selectivity of transition‐metal catalysts for cross‐coupling reactions. To this end, we have used the activation strain model to quantum‐chemically analyze the activity of catalyst complexes d10‐M(L)n toward methane C?H oxidative addition. We studied the effect of varying the metal center M along the nine d10 metal centers of Groups 9, 10, and 11 (M=Co?, Rh?, Ir?, Ni, Pd, Pt, Cu+, Ag+, Au+), and, for completeness, included variation from uncoordinated to mono‐ to bisligated systems (n=0, 1, 2), for the ligands L=NH3, PH3, and CO. Three concepts emerge from our activation strain analyses: 1) bite‐angle flexibility, 2) d‐regime catalysts, and 3) s‐regime catalysts. These concepts reveal new ways of tuning a catalyst’s activity. Interestingly, the flexibility of a catalyst complex, that is, its ability to adopt a bent L‐M‐L geometry, is shown to be decisive for its activity, not the bite angle as such. Furthermore, the effect of ligands on the catalyst’s activity is totally different, sometimes even opposite, depending on the electronic regime (d or s) of the d10‐M(L)n complex. Our findings therefore constitute new tools for a more rational design of catalysts. 相似文献