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Reduction of Alkenes: Catalytic Hydrogenation02:13

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 surface of...
Heterogeneous Catalysis01:22

Heterogeneous Catalysis

Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation01:28

Reduction of Benzene to Cyclohexane: Catalytic Hydrogenation

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...
Hydroboration-Oxidation of Alkenes03:08

Hydroboration-Oxidation of Alkenes

In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

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...
Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide02:44

Oxidation of Alkenes: Syn Dihydroxylation with Osmium Tetraoxide

Alkenes are converted to 1,2-diols or glycols through a process called dihydroxylation. It involves the addition of two hydroxyl groups across the double bond with two different stereochemical approaches, namely anti and syn. Dihydroxylation using osmium tetroxide progresses with syn stereochemistry.

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Updated: Jun 18, 2026

Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
10:21

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

Published on: October 5, 2019

Hydrogen evolution catalyzed by cobaloximes.

Jillian L Dempsey1, Bruce S Brunschwig, Jay R Winkler

  • 1Beckman Institute, California Institute of Technology, Pasadena, California 91125, USA.

Accounts of Chemical Research
|November 26, 2009
PubMed
Summary
This summary is machine-generated.

Scientists are developing artificial photosynthesis for solar-driven water splitting. Cobalt complexes (cobaloximes) efficiently catalyze hydrogen gas production via a homolytic pathway, overcoming barriers in other routes.

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A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions
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Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production
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Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

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Developing Photosensitizer-Cobaloxime Hybrids for Solar-Driven H2 Production in Aqueous Aerobic Conditions
10:21

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A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions
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Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production
08:40

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

Published on: December 6, 2021

Area of Science:

  • Artificial photosynthesis
  • Catalysis
  • Renewable energy

Background:

  • Natural photosynthesis converts light energy into chemical energy.
  • Artificial systems aim for solar-driven water splitting to produce hydrogen fuel.
  • Efficient catalysts for proton reduction to H(2) are crucial for artificial photosynthesis.

Purpose of the Study:

  • To explore cobalt complexes with diglyoxime ligands (cobaloximes) as catalysts for proton reduction.
  • To analyze the thermodynamic pathways of hydrogen evolution catalyzed by cobaloximes.
  • To identify rate-limiting steps and barriers in cobaloxime-catalyzed hydrogen production.

Main Methods:

  • Chemical, electrochemical, and photochemical methods were used to study cobaloxime catalysis.
  • Thermodynamic analysis was performed on H(2) evolution pathways.
  • Experimental results were combined with thermodynamic insights.

Main Results:

  • Cobaloxime complexes catalyze proton reduction to H(2).
  • Two pathways, homolytic and heterolytic, were identified for H(2) evolution.
  • The homolytic pathway, involving Co(III)-hydrides, exhibits lower activation barriers than the heterolytic pathway.
  • Formation of Co(III)-diglyoxime presents a significant barrier in the heterolytic route.
  • Hydride formation is identified as the rate-limiting step.

Conclusions:

  • Cobaloximes are promising catalysts for solar-driven water splitting.
  • The homolytic pathway is thermodynamically favored for H(2) evolution.
  • Optimizing catalyst design for efficient hydride formation is key.
  • Tethering catalysts to electrode surfaces requires careful consideration to maintain catalytic efficiency.