Catalysts featuring a metal-nitrogen bond are capable of transferring nitrogen to organic molecules. Short-lived molecular species that are formed in this process have properties that crucially decide the course of the reaction and also the formation of a product.
Chemists from the University of Göttingen and Goethe University Frankfurt have thoroughly analyzed the major compound formed in a catalytic nitrogen-atom transfer reaction. The in-depth understanding of this catalytic nitrogen-atom transfer reaction will enable the development of new catalysts that are customized for particular reactions.
Molecules have to be specifically modified to develop innovative molecular materials or novel drugs with new properties. One of the main objectives of catalysis is the selectivity control in these chemical changes. This is specifically true in the case of complex molecules that have numerous reactive sites to prevent unwanted waste for better sustainability.
For example, a specifically fascinating goal of chemical synthesis is the selective introduction of individual nitrogen atoms into the carbon-hydrogen bonds of the molecules of interest.
Previously, such kinds of nitrogen transfer reactions were hypothesized on the basis of quantum-chemical computer simulations for molecular metal complexes in which individual nitrogen atoms are attached to the metal.
But such highly reactive intermediates were previously overlooked during experimental observations. Therefore, a closely entangled combination of theoretical and experimental analyses is crucial for a comprehensive analysis of these key metallonitrene intermediates and, eventually, the manipulation of catalytic nitrogen-atom transfer reactions.
For the first time, chemists were able to directly visualize this metallonitrene, quantify it spectroscopically, and offer a detailed quantum-chemical characterization. The chemists are part of the groups of Professor Sven Schneider from the University of Göttingen, and Professor Max Holthausen from Goethe University Frankfurt, in association with the teams of Professor Joris van Slagern from the University of Stuttgart and Professor Bas de Bruin from the University of Amsterdam.
As such, the team photochemically converted a platinum azide complex into a metallonitrene and through photo-crystallography, examined both materials magnetometrically.
Along with theoretical modeling, the teams have now given an in-depth report on a highly reactive metallonitrene diradical that features a single bond of metal and nitrogen. Moreover, the researchers were able to demonstrate how the unique electronic structure of the platinum metallonitrene enables the nitrogen atom to be selectively inserted into, for instance, the C–H bonds of other kinds of molecules.
The findings of our work significantly extend the basic understanding of chemical bonding and reactivity of such metal complexes, providing the basis for a rational synthesis planning."
Max Holthausen, Professor, Goethe University Frankfurt
Professor Sven Schneider added, “These insertion reactions allow the use of metallonitrenes for the selective synthesis of organic nitrogen compounds through catalyst nitrogen atom transfer. This work, therefore, contributes to the development of novel ‘green’ syntheses of nitrogen compounds.”
The study was financially sported y the Deutsche Forschungsgemeinschaft and the European Research Council.
Sun, J., et al. (2020) A platinum(II) metallonitrene with a triplet ground state. Nature Chemistry. doi.org/10.1038/s41557-020-0522-4.