Chemists discover new reactivity of strained molecules

In synthetic organic chemistry, cycloadditions are an important class of reactions. A ring-shaped molecule can be created by joining two compounds that have double bonds. A team led by Prof. Dr. Frank Glorius from the University of Münster has succeeded in performing an unconventional cycloaddition in which a carbon-carbon double bond reacts with a carbon-carbon single bond. In double bonds, atoms are connected by two pairs of electrons; in single bonds, only one pair of electrons is involved. The key to success was the use of single bonds. The chemists used a catalyst that uses light energy to drive the reaction. The study was published in the journal Nature.

Roman Kleinmans explains that the method has a synthetic benefit because it can be used to build polycyclic, three-dimensional carbon scaffolds that have been difficult or impossible to access. Three-dimensional architectures are fascinating and play an increasingly important role in chemistry.

The chemistry is detailed.

For more than a century, photocycloadditions have been studied and developed. Two double bonds react to form two new single bonds and give a four-membered ring product. This type of reaction using a single bond has been achieved by the team from MFC.

The team used a class of compounds with single bonds. The carbon compounds have a butterfly-like shape with two triangles on a single bond that looks like wings. The internal wing angles are different from the ideal unstrained angles. The carbon-carbon double bond is favored by the strain energy released by the opening of the central single bond. The researchers succeeded in incorporating a nitrogen atom into the product.

The visible light driven triplet-triplet energy transfer catalysis allows the reaction to be carried out as lightly as possible, so that irradiation of the reaction with harsh UV light, which is commonly used in chemistry of this type, was not needed. The catalyst absorbs energy from the irradiated light and transfers it to a suitable surface. The catalyst is regenerated and the molecule is left in a triplet state. The molecule can react with the single bond using a simple organic photosensitizer. Computational calculations were carried out to understand the mechanism of the reaction in more detail.

More information: Roman Kleinmans et al, Intermolecular [2π+2σ]-photocycloaddition enabled by triplet energy transfer, Nature (2022). DOI: 10.1038/s41586-022-04636-x Journal information: Nature Citation: Chemists discover new reactivity of strained molecules (2022, March 23) retrieved 23 March 2022 from https://phys.org/news/2022-03-chemists-reactivity-strained-molecules.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.