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Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

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...

Reduction of Alkenes: Catalytic Hydrogenation

Reduction of Alkenes: Catalytic Hydrogenation

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.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.

Catalysis

Catalysis

The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.

meta-Directing Deactivators: –NO2, –CN, –CHO, –&NoBreak;CO2R, –COR, –CO2H

meta-Directing Deactivators: –NO₂, –CN, –CHO, –⁠CO₂R, –COR, –CO₂H

All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for...

Photochemical Electrocyclic Reactions: Stereochemistry

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The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation

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Related Experiment Video

Updated: Aug 26, 2025

Light-driven Enzymatic Decarboxylation

Light-driven Enzymatic Decarboxylation

Published on: May 22, 2016

Catalytic Reversible (De)hydrogenation To Rotate a Chemically Fueled Molecular Switch.

Enzo Olivieri¹, Na Shao¹, Roselyne Rosas²

¹Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France.

Angewandte Chemie (International Ed. in English)

|October 13, 2022

Summary

Researchers developed a novel rotating molecular switch using metal-catalyzed reactions. This switch reversibly converts between alcohol and ketone forms, enabling 180° rotation without waste, paving the way for advanced molecular machines.

Keywords:

Catalysis Conformation Green Chemistry Hydrogenation Molecular Switch

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A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

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Last Updated: Aug 26, 2025

Light-driven Enzymatic Decarboxylation

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Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes

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A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Published on: February 16, 2020

Area of Science:

Molecular Machines
Organic Chemistry
Catalysis

Background:

Developing molecular machines requires precise control over molecular motion.
Reversible chemical reactions are key to creating controllable molecular switches.
Metal-catalyzed reactions offer efficient pathways for chemical transformations.

Purpose of the Study:

To engineer a rotating molecular switch.
To utilize metal-catalyzed reversible (de)-hydrogenation for molecular switching.
To achieve 180° rotation in a molecular system.

Main Methods:

Employing metal catalysts for acceptorless dehydrogenation and hydrogenation.
Utilizing a tolane scaffold for the molecular switch design.
Operating the switch under argon and hydrogen pressure stimuli.

Main Results:

Demonstrated reversible conversion between alcohol and ketone states.
Achieved 180° rotation of the molecular switch.
Confirmed the absence of waste accumulation during the switching process.

Conclusions:

A novel rotating molecular switch based on reversible (de)-hydrogenation was successfully developed.
The metal-catalyzed system offers a waste-free approach for molecular switching.
This technology holds potential for designing sophisticated molecular machines.