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Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...

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Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
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Thermal and Photochemical Electrocyclic Reactions: Overview

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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.

Catalysis

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Unlike the easy catalytic hydrogenation of an alkene double bond, hydrogenation of a benzene double bond under similar reaction conditions does not take place easily. For example, in the reduction of stilbene, the benzene ring remains unaffected while the alkene bond gets reduced. Hydrogenation of an alkene double bond is exothermic and a favorable process. In contrast, to hydrogenate the first unsaturated bond of benzene, an energy input is needed; that is, the process is endothermic. This is...

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Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

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Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions

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Electrocatalytic H₂ evolution using binuclear cobalt complexes as catalysts.

Tung H To^1,2, Dang B Tran^2,3, Vu Thi Thu Ha⁴

¹Graduate University of Science and Technology, Vietnam Academy of Science and Technology 18 Hoang Quoc Viet Hanoi Vietnam to-hai.tung@usth.edu.vn.

|October 24, 2022

Summary

This summary is machine-generated.

Two binuclear cobalt complexes efficiently catalyze hydrogen (H2) evolution using acetic acid. Independent cobalt centers operate without synergy, achieving high faradaic efficiency and a turnover frequency of 50 s-1.

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Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Published on: April 10, 2018

Area of Science:

Inorganic Chemistry
Catalysis
Electrochemistry

Background:

Hydrogen (H2) evolution is crucial for renewable energy technologies.
Developing efficient and cost-effective catalysts for H2 production is a key research area.
Binuclear metal complexes offer potential for enhanced catalytic activity through cooperative effects.

Purpose of the Study:

To investigate the catalytic activity of two binuclear cobalt complexes with a specific ligand for H2 evolution.
To elucidate the mechanism and efficiency of these cobalt catalysts in hydrogen production.
To determine if the two cobalt centers exhibit synergistic behavior during catalysis.

Main Methods:

Synthesis and characterization of two binuclear cobalt complexes.
Electrochemical analysis, including cyclic voltammetry and bulk electrolysis.
Spectroscopic analysis to study catalyst behavior.
Theoretical analysis using foot-of-the-wave analysis to understand the catalytic mechanism.

Main Results:

The binuclear cobalt complexes effectively catalyzed H2 evolution in DMF with acetic acid.
An overpotential of approximately 470 mV was required for H2 evolution.
Faradaic efficiency for H2 generation ranged from 85-95% after 5 hours of electrolysis.
Kinetic studies indicated a maximum turnover frequency (TOF) of 50 s-1, consistent with an ECEC mechanism.
The two cobalt centers, separated by 4.175 Å, operated independently without synergistic effects.

Conclusions:

The studied binuclear cobalt complexes are effective catalysts for hydrogen evolution.
Catalysis proceeds via an ECEC mechanism with independent operation of the cobalt centers.
The lack of synergy suggests potential for further optimization by modifying the ligand or metal center proximity.