25068-25-1Relevant articles and documents
Contra-thermodynamic Olefin Isomerization by Chain-Walking Hydroboration and Dehydroboration
Bloomer, Brandon,Butcher, Trevor W.,Ciccia, Nicodemo R.,Conk, Richard J.,Hanna, Steven,Hartwig, John F.
, p. 1005 - 1010 (2022/02/10)
We report a dehydroboration process that can be coupled with chain-walking hydroboration to create a one-pot, contra-thermodynamic, short-or long-range isomerization of internal olefins to terminal olefins. This dehydroboration occurs by a sequence comprising activation with a nucleophile, iodination, and base-promoted elimination. The isomerization proceeds at room temperature without the need for a fluoride base, and the substrate scope of this isomerization is expanded over those of previous isomerizations we have reported with silanes.
Diverse Mechanistic Pathways in Single-Site Heterogeneous Catalysis: Alcohol Conversions Mediated by a High-Valent Carbon-Supported Molybdenum-Dioxo Catalyst
Bedzyk, Michael J.,Das, Anusheela,Kratish, Yosi,Li, Jiaqi,Ma, Qing,Marks, Tobin J.
, p. 1247 - 1257 (2022/02/07)
With the increase in the importance of renewable resources, chemical research is shifting focus toward substituting petrochemicals with biomass-derived analogues and platform-molecule transformations such as alcohol processing. To these ends, in-depth mechanistic understanding is key to the rational design of catalytic systems with enhanced activity and selectivity. Here we discuss in detail the structure and reactivity of a single-site active carbon-supported molybdenum-dioxo catalyst (AC/MoO2) and the mechanism(s) by which it mediates alcohol dehydration. A range of tertiary, secondary, and primary alcohols as well as selected bio-based terpineols are investigated as substrates under mild reaction conditions. A combined experimental substituent effect/kinetic/kinetic isotope effect/EXAFS/DFT computational analysis indicates that (1) water assistance is a key element in the transition state; (2) the experimental kinetic isotopic effect and activation enthalpy are 2.5 and 24.4 kcal/mol, respectively, in good agreement with the DFT results; and (3) several computationally identified intermediates including Mo-oxo-hydroxy-alkoxide and cage-structured long-range water-coordinated Mo-dioxo species are supported by EXAFS. This structurally and mechanistically well-characterized single-site system not only effects efficient transformations but also provides insight into rational catalyst design for future biomass processes.
Phosphorus and nitrogen-doped palladium nanomaterials support on coral-like carbon materials as the catalyst for semi-hydrogenation of phenylacetylene and mechanism study
Ma, Lei,Jiang, Pengbo,Wang, Kaizhi,Lan, Kai,Huang, Xiaokang,Yang, Ming,Gong, Li,Jia, Qi,Mu, Xiao,Xiong, Yucong,Li, Rong
, (2021/02/26)
In this work, two types of polyporous and coral-like materials (CN) with high specific surface area are prepared using sodium glutamate as a carrier. At the same time, a CN-supported phosphorus-nitrogen-doped palladium nanomaterial CN-P-Pd is synthesized and applied to the preparation of styrene by selective hydrogenation of phenylacetylene under mild conditions. As shown in the TEM images, Pd nanoparticles with a particle size of about 4.4 nm are uniformly dispersed on the surface of the carrier. The results of N2 adsorption–desorption reveal that the surface area of the prepared catalyst (CN-P-Pd) is 1307 m2g?1. In addition, the experimental exploration shows the intervention of P in carbon-nitrogen materials can contribute to improve the selectivity of the reaction, which can be attributed to the fact that P element can change the electron density of Pd. Meanwhile, it is found that the solvent not only affects the activity of catalyst, but also the selectivity of the reaction. Kinetic study shows the activation energy of the reaction is 4.5 kJ/mol. With the increase of the reaction temperature, the dissolution rate of hydrogen in the solvent gradually slows down, which inhibits the progress of the reduction reaction. Mechanistic studies demonstrate that the carbon-nitrogen materials have strong adsorption capacity for substrates, and also provide more adsorption sites for phenylacetylene. Additionally, the optimal catalyst (CN-P-Pd) also has high reaction activity to other alkynes and the conversion can reach at 95%. Moreover, the optimal catalyst can be reused several times without significant reduction in reaction activity.
