Structural Evidence for Lewis Acid Triggered Nitrosyl Bending in Rhenium(-I) Chloro Catalysts for Alkene Hydrogenation Reactions

2013 ◽  
Vol 2014 (1) ◽  
pp. 140-147 ◽  
Author(s):  
Yanfeng Jiang ◽  
Wenjing Huang ◽  
Helmut W. Schmalle ◽  
Olivier Blacque ◽  
Thomas Fox ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Hydrogenation Reactions ◽  
Alkene Hydrogenation

Intramolecular Lewis pairs with two acid sites – reactivity differences between P- and N-based systems

2016 ◽  
Vol 45 (43) ◽  
pp. 17319-17328 ◽  
Author(s):  
Leif A. Körte ◽  
Sebastian Blomeyer ◽  
Shari Heidemeyer ◽  
Jan Hendrick Nissen ◽  
Andreas Mix ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Acid Sites ◽  
Catalytically Active ◽  
Hydrogenation Reactions ◽  
Dynamic Exchange ◽  
Lewis Pairs

Unlike the aniline PhN[(CH2)3B(C6F5)2]2 the doubly hydroborated species (tBu/Ph)P[(CH2)3B(C6F5)2]2 show no dynamic exchange of the boron Lewis acid functions in solution and are not catalytically active in terms of H/D-scrambling as well as hydrogenation reactions.

scholarly journals Comparison of alkene hydrogenation in carbon nanoreactors of different diameters: probing the effects of nanoscale confinement on ruthenium nanoparticle catalysis

2017 ◽  
Vol 5 (40) ◽  
pp. 21467-21477 ◽  
Author(s):  
Mehtap Aygün ◽  
Craig T. Stoppiello ◽  
Maria A. Lebedeva ◽  
Emily F. Smith ◽  
Maria del Carmen Gimenez-Lopez ◽  
...  
Keyword(s):  
Chemical Reactions ◽  
Optimum Level ◽  
Control Chemical ◽  
Competitive Hydrogenation ◽  
Hydrogenation Reactions ◽  
Alkene Hydrogenation ◽  
Nanoparticle Catalysis ◽  
Different Diameters

Exploratory, competitive hydrogenation reactions reveal the optimum level of confinement to control chemical reactions.

Synthesis and Applications of Chiral Bicyclic Bisborane Catalysts

Synthesis ◽  
2021 ◽  
Author(s):  
Zhao-Ying Yang ◽  
Ming Zhang ◽  
Xiao-Chen Wang
Keyword(s):  
Transition Metal ◽  
Lewis Acid ◽  
Asymmetric Hydrogenation ◽  
Acid Catalysts ◽  
Frustrated Lewis Pairs ◽  
Lewis Acid Catalysts ◽  
Lewis Bases ◽  
Metal Free ◽  
Hydrogenation Reactions ◽  
Acid Catalyzed

The development of chiral borane Lewis acid catalysts opened the door for transition-metal-free catalyzed asymmetric organic reactions. Herein, we have summarized our work on the preparation of two classes of novel chiral bicyclic bisborane Lewis acid catalysts derived from C2-symmetric [3.3.0] dienes and [4.4] dienes, respectively. These catalysts not only form frustrated Lewis pairs with Lewis bases to catalyze asymmetric hydrogenation reactions but also activate Lewis basic functional groups in traditional Lewis acid catalyzed asymmetric reactions.

scholarly journals Mechanisms of Alkene and Diene Hydrogenation Reactions in H-MFI and H-CHA Zeolite Frameworks During MTO

2019 ◽  
Author(s):  
Mykela DeLuca ◽  
Christina Janes ◽  
David Hibbitts
Keyword(s):  
Selective Hydrogenation ◽  
Density Functional ◽  
High Pressures ◽  
Catalyst Deactivation ◽  
Zeolite Catalysts ◽  
As Species ◽  
Methanol To Olefin ◽  
Hydrogenation Reactions ◽  
Alkene Hydrogenation ◽  
Thermodynamic Instability

<p>Co-feeding H<sub>2</sub> at high pressures increases zeolite catalyst lifetimes during methanol-to-olefin (MTO) reactions while maintaining high alkene-to-alkane ratios; however, the mechanisms and species hydrogenated by H<sub>2</sub> co-feeds to prevent catalyst deactivation remain unknown. This study uses periodic density functional theory (DFT) to examine hydrogenation mechanisms of MTO product C<sub>2</sub>–C<sub>4</sub> alkenes, as well as species related to the deactivation of MTO catalysts such as C<sub>4</sub> and C<sub>6</sub> dienes, benzene, and formaldehyde in H-MFI and H-CHA zeolite catalysts. Results show that dienes and formaldehyde are selectively hydrogenated in both frameworks at MTO conditions because their hydrogenation transition states proceed via allylic and oxocarbenium cations which are more stable than alkylcarbenium ions which mediate alkene hydrogenation. Diene hydrogenation is further stabilized by protonation and hydridation at α,δ positioned C-atoms to form 2-butene from butadiene and 3-hexene from hexadiene as primary hydrogenation products. This α,δ-hydrogenation directly leads to selective hydrogenation of dienes; pathways which hydrogenate dienes at the α,β-position (e.g., forming 1-butene from butadiene) proceed with barriers 20 kJ mol<sup>-1</sup> higher than α,δ-hydrogenation and with barriers nearly equivalent to butene hydrogenation, despite α,β-hydrogenation of butadiene also occurring through allylic carbocations. Hydrogenation of formaldehyde, a diene precursor, occurs with barriers that are within 15 kJ mol<sup>-1</sup> of diene hydrogenation barriers, indicating that it may also contribute to increasing catalyst lifetimes by preventing diene formation. Benzene, in contrast to dienes and formaldehyde, is hydrogenated with higher barriers than C<sub>2</sub>–C<sub>4</sub> alkenes despite proceeding via stable benzenium cations because of the thermodynamic instability of the product which has lost aromaticity. Carbocation stabilities predict the relative rates of alkene hydrogenation and in some cases shed insights into the hydrogenation of benzene, dienes, and formaldehyde, but cation stabilities alone cannot account for the poor hydrogenation of benzene or the facile hydrogenation of dienes, boosted by stabilization conferred by a,δ-hydrogenation. This work suggests that the main mechanisms of catalyst lifetime improvement with high H<sub>2</sub> co-feeds is reduction of diene concentrations through both their selective hydrogenation and hydrogenation of their precursors to prevent formation of deactivating polyaromatic species.</p>

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

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