Related Experiment Video
Updated: May 19, 2026
09:35
Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
Published on: September 18, 2016
Mechanisms by which alkynes react with CpCr(CO)3H. Application to radical cyclization
Deven P Estes1, Jack R Norton, Steffen Jockusch
1Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, USA.
Journal of the American Chemical Society
|August 21, 2012
Summary
This study investigates the reaction of CpCr(CO)(3)H with activated alkynes, revealing distinct mechanisms like hydrogen atom transfer (HAT) and single electron transfer (SET) in hydrogenation and cyclization reactions.
Area of Science:
- Organometallic Chemistry
- Reaction Mechanisms
- Catalysis
Background:
- CpCr(CO)(3)H is a known reducing agent.
- Activated alkynes are versatile substrates in organic synthesis.
- Understanding reaction pathways is crucial for catalyst design.
Purpose of the Study:
- To elucidate the reaction mechanisms of CpCr(CO)(3)H with activated alkynes.
- To investigate the kinetics and stereochemistry of alkyne hydrogenation.
- To explore catalytic applications for cyclization reactions.
Main Methods:
- Kinetic studies of reactions in benzene.
- Stereochemical analysis of hydrogenation products.
- Electron Paramagnetic Resonance (EPR) spectroscopy to detect radical intermediates.
- Catalytic hydrogenation using a cobaloxime catalyst.
Main Results:
- Phenylacetylene and diphenylacetylene hydrogenation proceed via a hydrogen atom transfer (HAT) mechanism.
- Dimethyl acetylenedicarboxylate (DMAD) reaction involves hydrogenation and phenyl substitution, potentially via a single electron transfer (SET) pathway.
- EPR spectroscopy confirmed the formation of a radical anion intermediate during the DMAD reaction.
- An aromatic 1,6 eneyne underwent cyclization to yield 78% cyclized products under catalytic conditions.
- A cobaloxime catalyst completely eliminated hydrogenation, yielding 100% cyclized products.
Conclusions:
- CpCr(CO)(3)H exhibits diverse reactivity with activated alkynes, including HAT and SET mechanisms.
- Catalytic systems can selectively promote cyclization over hydrogenation.
- The study provides insights into organometallic reaction pathways and catalytic transformations.
![[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F59739.jpg&w=3840&q=50)
Related Concept Videos
02:24Reduction 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.
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.
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
02:27Preparation of Alkynes: Alkylation Reaction
Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
01:22Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction
The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.
01:16Radical Reactivity: Nucleophilic Radicals
Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For instance, consider...
02:34Preparation of Alkynes: Dehydrohalogenation
Introduction
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.