排序方式: 共有37条查询结果,搜索用时 15 毫秒
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Dr. Shaoguang Zhang Dr. Peng Cui Tianchang Liu Qiuran Wang Thomas J. Longo Laura M. Thierer Dr. Brian C. Manor Dr. Michael R. Gau Dr. Patrick J. Carroll Prof. Dr. Georgia C. Papaefthymiou Prof. Dr. Neil C. Tomson 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(35):15327-15331
Despite their connection to ammonia synthesis, little is known about the ability of iron-bound, bridging nitrides to form N−H bonds. Herein we report a linear diiron bridging nitride complex supported by a redox-active macrocycle. The unique ability of the ligand scaffold to adapt to the geometric preference of the bridging species was found to facilitate the formation of N−H bonds via proton-coupled electron transfer to generate a μ-amide product. The structurally analogous μ-silyl- and μ-borylamide complexes were shown to form from the net insertion of the nitride into the E−H bonds (E=B, Si). Protonation of the parent bridging amide produced ammonia in high yield, and treatment of the nitride with PhSH was found to liberate NH3 in high yield through a reaction that engages the redox-activity of the ligand during PCET. 相似文献
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Problems associated with the development of a new method for the diagnostics of gas flows, which is suitable for ballistic experiments, are considered. The method is based of shock wave sensing of the flow under investigation. Various methods are proposed for introducing sensing perturbations into the flow. These methods are used for measuring the parameters of a gas streamlining flying vehicles with the front stalling zone. 相似文献
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Gianetti TL Tomson NC Arnold J Bergman RG 《Journal of the American Chemical Society》2011,133(38):14904-14907
The discovery of a Nb(III)-mediated catalytic hydrogenation of internal alkynes to (Z)-alkenes that proceeds through an unprecedented mechanism is reported. The mechanistic proposal involves initial reduction of the alkyne by the Nb(III) complex (BDI)Nb(N(t)Bu)(CO)(2) to provide a Nb(V) metallacyclopropene, itself capable of σ-bond metathesis reactivity with H(2). The resulting alkenyl hydride species then undergoes reductive elimination to provide the (Z)-alkene product and regenerate a metal complex in the Nb(III) oxidation state. Support for the proposed mechanism is derived from (i) the dependence of the product selectivity on the relative concentrations of CO and H(2), (ii) the isolation of complexes closely related to those proposed to be part of the catalytic cycle, (iii) H/D crossover experiments, and (iv) DFT studies of multiple possible reaction pathways. 相似文献
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The linear additivity of free energies of ionization of substituted acids relative to the unsubstituted parent acid is described in terms of the Hammett relationship and as the weighted sums of microscopic free energies for benzenetricarboxylic acids. 相似文献
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Tomson NC Yan A Arnold J Bergman RG 《Journal of the American Chemical Society》2008,130(34):11262-11263
The reaction of carbon monoxide with a beta-diketiminato dimethyl niobium complex (BDI)Me2Nb(NtBu) is shown to lead to a variety of products whose distribution displays a remarkable dependence on the reaction conditions. Among these, the products of metal reduction, enediolate formation, and intramolecular C-H activation have been fully characterized. An investigation into the individual steps leading to these products points to a transient initial monoacyl complex, whose fate may be perturbed via reaction conditions to allow for control over the product distribution. Furthermore, the reaction of (BDI)Me2Nb(NCMe3) with XylNC (Xyl = 2,6-Me2C6H3) yields the eta2-ketimine complex (BDI)(Me2C=NXyl)Nb(NCMe3), whose characterization and reactivity enhance our understanding of the sequences involving CO. 相似文献
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In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco... 相似文献
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Márcio AF Belo-Filho Franklina MB Toledo Bernardo Almada-Lobo 《The Journal of the Operational Research Society》2014,65(11):1735-1747
Setup operations are significant in some production environments. It is mandatory that their production plans consider some features, as setup state conservation across periods through setup carryover and crossover. The modelling of setup crossover allows more flexible decisions and is essential for problems with long setup times. This paper proposes two models for the capacitated lot-sizing problem with backlogging and setup carryover and crossover. The first is in line with other models from the literature, whereas the second considers a disaggregated setup variable, which tracks the starting and completion times of the setup operation. This innovative approach permits a more compact formulation. Computational results show that the proposed models have outperformed other state-of-the-art formulation. 相似文献
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Alexander B. Weberg Samuel P. McCollom Laura M. Thierer Michael R. Gau Patrick J. Carroll Neil C. Tomson 《Chemical science》2021,12(12):4395
A series of tetradentate tris(phosphinimine) ligands (R3P3tren) was developed and bound to CuI to form the trigonal pyramidal, C3v-symmetric cuprous complexes [R3P3tren-Cu][BArF4] (1PR3) (PR3 = PMe3, PMe2Ph, PMePh2, PPh3, PMe2(NEt2), BArF4 = B(C6F5)4). Electrochemical studies on the CuI complexes were undertaken, and the permethylated analog, 1PMe3, was found to display an unprecedentedly cathodic CuI/CuII redox potential (−780 mV vs. Fc/Fc+ in isobutyronitrile). Elucidation of the electronic structures of 1PR3via density functional theory (DFT) studies revealed atypical valence manifold configurations, resulting from strongly σ-donating phosphinimine moieties in the xy-plane that destabilize 2e (dxy/dx2−y2) orbital sets and uniquely stabilized a1 (dz2) orbitals. Support is provided that the a1 stabilizations result from intramolecular electrostatic fields (ESFs) generated from cationic character on the phosphinimine moieties in R3P3tren. This view is corroborated via 1-dimensional electrostatic potential maps along the z-axes of 1PR3 and their isostructural analogues. Experimental validation of this computational model is provided upon oxidation of 1PMe3 to the cupric complex [Me3P3tren-Cu][OTf]2 (2PMe3), which displays a characteristic Jahn–Teller distortion in the form of a see-saw, pseudo-Cs-symmetric geometry. A systematic anodic shift in the potential of the CuI/CuII redox couple as the steric bulk in the secondary coordination sphere increases is explained through the complexes'' diminishing ability to access the ideal Cs-symmetric geometry upon oxidation. The observations and calculations discussed in this work support the presence of internal electrostatic fields within the copper complexes, which subsequently influence the complexes'' properties via a method orthogonal to classic ligand field tuning.Secondary coordination sphere electrostatic effects tune the valence manifolds of copper centers, impacting molecular geometries, photophysical properties, and redox potentials. 相似文献