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Electrophilic Addition to Alkynes: Halogenation

Electrophilic 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.

Cycloaddition Reactions: Overview

Cycloaddition Reactions: Overview

Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.

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.

Electrophilic Addition to Alkynes: Hydrohalogenation

Electrophilic Addition to Alkynes: Hydrohalogenation

Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.

Preparation of Alkynes: Alkylation Reaction

Preparation 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.

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Updated: Jan 6, 2026

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Published on: April 10, 2015

Square-Planar Ruthenium Alkylidyne Complexes Undergo Stepwise Rather Than Concerted [2 + 2] Cycloadditions with

Mingxu Cui¹, Markus Leutzsch¹, Alexander A Auer¹

¹Max-Planck-Institut für Kohlenforschung, Mülheim/Ruhr, 45470, Germany.

Angewandte Chemie (International Ed. in English)

|November 10, 2025

Summary

This summary is machine-generated.

Researchers developed new ruthenium alkylidyne complexes for novel chemical reactions. These d4-configured complexes exhibit a unique stepwise mechanism in cycloaddition reactions, differing from traditional methods.

Keywords:

Alkylidyne complexes Alkyne metathesis Metallacyclobutadiene Ruthenium [2 + 2] Cycloaddition

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Published on: September 18, 2016

Area of Science:

Organometallic Chemistry
Catalysis
Synthetic Chemistry

Background:

Ruthenium alkylidyne complexes are important in catalysis.
Existing research primarily focuses on d0 and d2 metal alkylidynes for alkyne metathesis.

Purpose of the Study:

To synthesize and characterize new square-planar, d4-configured ruthenium alkylidyne complexes.
To investigate the reactivity of these complexes in cycloaddition reactions with various alkynes.

Main Methods:

Utilized p-tolyl(trimethylsilyl)diazomethane as an alkylidyne synthon.
Employed an electron-rich PNP-pincer ligand to support the ruthenium complex.
Studied the [2+2] cycloaddition reactions with diverse alkynes.

Main Results:

Successfully synthesized a novel d4-ruthenium alkylidyne complex (complex 12).
Demonstrated facile [2+2] cycloaddition of complex 12 with electron-rich, electron-deficient, and strained alkynes.
Observed a stepwise reaction mechanism, distinct from the concerted mechanism of d0 and d2 analogues.
Attributed the unique reactivity to the non-bonding lone pair in the metal-centered HOMO.

Conclusions:

The study introduces a new class of d4-ruthenium alkylidyne complexes.
The findings reveal a novel stepwise cycloaddition mechanism, challenging existing paradigms in alkyne metathesis.
The insights gained will facilitate further exploration of d4-metal alkylidyne chemistry.