'Radical' approach yields catalyst for sustainable indene synthesis

Averting the use of noble metals through bio-inspired metallo-radical catalysis

6 July 2016

A team of scientists of the University of Amsterdam's research priority area Sustainable Chemistry has developed a new catalyst for the easy synthesis of substituted 1H-indenes. Based on the abundant element cobalt their cheap and easy to prepare catalytic complex is capable of the sustainable concept of metalloradical catalysis. Details have recently been published on the website of the Journal of the American Chemical Society.

Indenes are valuable building blocks of a variety of natural products, pharmaceuticals and other bio-active compounds. They also have widespread applications in metal complexes for catalytic use in e.g. olefin polymerization. As such, there is a demand for the development of fast, efficient and broadly applicable methods for indene synthesis from readily available starting materials.

Bio-inspired approach

Prof Bas de Bruin, professor Bio-inspired sustainable catalysis

Professor Bas de Bruin. Photo by Jeroen Oerlemans.

The strategy now reported by the UvA's SusChem team contributes to this development by providing a sustainable catalytic route to indene synthesis. It resulted from their new, bio-inspired approach in the field of so-called metallo-radical catalysis. Here the intrinsic radical-type reactivity of first row transition metals is utilized, where most currently applied catalytic approaches are aimed at preventing radical formation.

According to research leader Bas de Bruin the concept of metallo-radical catalysis enables chemists to move away from the current use of expensive noble metal catalysts and use cheap metals instead. Inspired by the performance of natural metallo-enzymes, De Bruin and his co-workers at the UvA's research priority area Sustainable Chemistry are currently developing more future catalysts also based on the concept of radical reactivity. 

Thermolysis of the applied tosyl hydrazones (easily prepared by condensation of the corresponding aldehydes with tosyl hydrazine) leads to in situ formation of the corresponding diazo compounds. The latter are activated by the catalyst, thus forming the key carbene-radical intermediates responsible for radical-type ring-closure to form the final indene products. The reaction has a broad substrate scope, tolerant to various different substituents, enabling facile synthesis of a variety of indene derivatives. Image: HIMS / Homkat.

Publication

Das, B.G.; Chirila, A.; Tromp, M.; Reek, J.N.H; de Bruin, B.: CoIII-Carbene Radical Approach to Substituted 1H-Indenes J. Am. Chem. Soc. 2016 Published online June 24, 2016 DOI:10.1021/jacs.6b05434

Published by  HIMS