Investigation of Lewis Acid versus Lewis Base Catalysis in Asymmetric Cyanohydrin Synthesis

2010 ◽  
Vol 16 (37) ◽  
pp. 11367-11375 ◽  
Author(s):  
Michael North ◽  
Marta Omedes-Pujol ◽  
Courtney Williamson
Keyword(s):  
Lewis Acid ◽  
Lewis Base ◽  
Base Catalysis ◽  
Acid Versus ◽  
Cyanohydrin Synthesis

scholarly journals Multifunctional heterocyclic scaffolds for hybrid Lewis acid/Lewis base catalysis of carbon–carbon bond formation

Tetrahedron ◽  
2016 ◽  
Vol 72 (27-28) ◽  
pp. 3905-3916 ◽  
Author(s):  
Dennis Wiedenhoeft ◽  
Adam R. Benoit ◽  
Yibiao Wu ◽  
Jacob D. Porter ◽  
Elisia Meyle ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Bond Formation ◽  
Lewis Base ◽  
Base Catalysis ◽  
Carbon Bond ◽  
Carbon Carbon Bond

scholarly journals Design and Synthesis of Oxazoline-Based Scaffolds for Hybrid Lewis Acid/Lewis Base Catalysis of Carbon–Carbon Bond Formation

Synthesis ◽  
2016 ◽  
Vol 48 (15) ◽  
pp. 2413-2422 ◽  
Author(s):  
Chris Dockendorff ◽  
Dennis Wiedenhoeft ◽  
Adam Benoit ◽  
Jacob Porter ◽  
Yibiao Wu ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Bond Formation ◽  
Lewis Base ◽  
Base Catalysis ◽  
Carbon Bond ◽  
Design And Synthesis ◽  
Carbon Carbon Bond

scholarly journals Oxoammonium salts are catalysing efficient and selective halogenation of olefins, alkynes and aromatics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Weijin Wang ◽  
Xinyao Li ◽  
Xiaoxue Yang ◽  
Lingsheng Ai ◽  
Zhiwen Gong ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Halogen Atom ◽  
Acid Catalysis ◽  
Lewis Base ◽  
Base Catalysis ◽  
Activation Model ◽  
Catalytic Systems ◽  
Oxoammonium Salts ◽  
The Past ◽  
Synergistic Activation

AbstractElectrophilic halogenation reactions have been a reliable approach to accessing organohalides. During the past decades, various catalytic systems have been developed for the activation of haleniums. However, there is still a short of effective catalysts, which could cover various halogenation reactions and broad scope of unsaturated compounds. Herein, TEMPO (2,2,6,6-tetramethylpiperidine nitroxide) and its derivatives are disclosed as active catalysts for electrophilic halogenation of olefins, alkynes, and aromatics. These catalysts are stable, readily available, and reactive enough to activate haleniums including Br+, I+ and even Cl+ reagents. This catalytic system is applicable to various halogenations including haloarylation of olefins or dibromination of alkynes, which were rarely realized in previous Lewis base catalysis or Lewis acid catalysis. The high catalytic ability is attributed to a synergistic activation model of electrophilic halogenating reagents, where the carbonyl group and the halogen atom are both activated by present TEMPO catalysis.

scholarly journals Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

2010 ◽  
Vol 6 ◽  
pp. 1043-1055 ◽  
Author(s):  
Michael North ◽  
Marta Omedes-Pujol
Keyword(s):  
Catalytic Activity ◽  
Propylene Carbonate ◽  
Lewis Base ◽  
Base Catalysis ◽  
Lewis Acidity ◽  
Mechanistic Study ◽  
Trimethylsilyl Cyanide ◽  
Trimethylsilyl Ethers ◽  
Rate Of Reaction ◽  
Cyanohydrin Synthesis

Propylene carbonate can be used as a green solvent for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding reactions carried out in dichloromethane. A mechanistic study has been undertaken, comparing the catalytic activity of VO(salen)NCS in propylene carbonate and dichloromethane. Reactions in both solvents obey overall second-order kinetics, the rate of reaction being dependent on the concentration of both the aldehyde and trimethylsilyl cyanide. The order with respect to VO(salen)NCS was determined and found to decrease from 1.2 in dichloromethane to 1.0 in propylene carbonate, indicating that in propylene carbonate, VO(salen)NCS is present only as a mononuclear species, whereas in dichloromethane dinuclear species are present which have previously been shown to be responsible for most of the catalytic activity. Evidence from 51V NMR spectroscopy suggested that propylene carbonate coordinates to VO(salen)NCS, blocking the free coordination site, thus inhibiting its Lewis acidity and accounting for the reduction in catalytic activity. This explanation was further supported by a Hammett analysis study, which indicated that Lewis base catalysis made a much greater contribution to the overall catalytic activity of VO(salen)NCS in propylene carbonate than in dichloromethane.

The structure and activity of potassium supported on SBA-15 molecular sieve: Density functional theory study

2014 ◽  
Vol 13 (01) ◽  
pp. 1350076 ◽  
Author(s):  
Bing Liu ◽  
Daxi Wang ◽  
Zhongxue Wang ◽  
Zhen Zhao ◽  
Yu Chen ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Lewis Acid ◽  
Molecular Sieve ◽  
Active Sites ◽  
Density Functional ◽  
Structural Model ◽  
Vibrational Frequencies ◽  
Oxygen Molecule ◽  
Lewis Base ◽  
Functional Theory

The geometries, vibrational frequencies, electronic properties and reactivity of potassium supported on SBA-15 have been theoretically investigated by the density functional theory (DFT) method. The structural model of the potassium supported on SBA-15 was constructed based on our previous work [Wang ZX, Wang DX, Zhao Z, Chen Y, Lan J, A DFT study of the structural units in SBA-15 mesoporous molecular sieve, Comput. Theor. Chem.963, 403, 2011]. This paper is the extension of our previous work. The most favored location of potassium atom was obtained by the calculation of substitution energy. The calculated vibrational frequencies of K /SBA-15 are in good agreement with the experimental results. By analyzing the properties of electronic structure, we found that the O atom of Si - O (2)- K group acts as the Lewis base center and the K atom acts as the Lewis acid center. The reactivity of K /SBA-15 was investigated by calculating the activation of oxygen molecule. The oxygen molecule can be activated by K /SBA-15 with an energy barrier of 103.2 kJ/mol. In the final state, the activated oxygen atoms become new Lewis acid centers, which are predicted to act as the active sites in the catalytic reactions. This study provides a deep insight into the properties of supported potassium catalysts and offers fundamental information for further research.

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