- Examining the Effects of Monomer and Catalyst Structure on the Mechanism of Ruthenium-Catalyzed Ring-Opening Metathesis Polymerization
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The mechanism of Ru-catalyzed ring-opening metathesis polymerization (ROMP) is studied in detail using a pair of third generation ruthenium catalysts with varying sterics of the N-heterocyclic carbene (NHC) ligand. Experimental evidence for polymer chelation to the Ru center is presented in support of a monomer-dependent mechanism for polymerization of norbornene monomers using these fast-initiating catalysts. A series of kinetic experiments, including rate measurements for ROMP, rate measurements for initiation, monomer-dependent kinetic isotope effects, and activation parameters were useful for distinguishing chelating and nonchelating monomers and determining the effect of chelation on the polymerization mechanism. The formation of a chelated metallacycle is enforced by both the steric bulk of the NHC and by the geometry of the monomer, leading to a ground-state stabilization that slows the rate of polymerization and also alters the reactivity of the propagating Ru center toward different monomers in copolymerizations. The results presented here add to the body of mechanistic work for olefin metathesis and may inform the continued design of catalysts for ROMP to access new polymer architectures and materials.
- Wolf, William J.,Lin, Tzu-Pin,Grubbs, Robert H.
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supporting information
p. 17796 - 17808
(2019/11/11)
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- ELECTROLYTE SOLUTION AND ELECTROCHEMICAL DEVICE
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The present invention aims to provide an electrolyte solution containing a quaternary ammonium salt as an electrolyte salt and is capable of providing an electrochemical device having a high capacitance retention and reducing generation of gas. The electrolyte solution of the present invention contains a solvent, a quaternary ammonium salt, and a nitrogen-containing unsaturated cyclic compound. The unsaturated cyclic compound is a nitrogen-containing unsaturated heterocyclic compound. The unsaturated cyclic compound excludes salts of the unsaturated cyclic compound and ionic liquids obtainable from the unsaturated cyclic compound.
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- The effect of temperature, catalyst and sterics on the rate of N-heterocycle dehydrogenation for hydrogen storage
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Efficient hydrogen storage is one of the critical requirements for the use of hydrogen fuel cells in light-duty vehicles. Our investigation of reversible chemical hydrogen storage systems has led to the development of a mixed endothermic-exothermic carrier system. Herein we further investigate the factors affecting the dehydrogenation rate of these carriers. A range of heterogeneous catalysts was synthesized via sol-gel methodology and their activity for indoline dehydrogenation was assessed. Metals used included Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir and Pt. SiO2, Al2O3, TiO2 and ZrO2 were used as supports and Pd/SiO2 gave the highest conversion over a fixed time. A marked increase in the rate of indoline dehydrogenation was observed when the temperature was increased between 100 and 180 °C, with measured first order rate constants of 1.8 × 10 -4 s-1 at 100 °C and 5.9 × 10-4 at 120 °C. Although piperidines dehydrogenate more slowly than indolines, steric hindrance around the nitrogen atom in piperidine increases its dehydrogenation rate significantly.
- Dean, Darrell,Davis, Boyd,Jessop, Philip G.
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body text
p. 417 - 422
(2011/04/21)
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