Taming “non-classical” carbocations: Prof. List and his team report a fundamental study in Nature Chemistry
Carbocations are short-lived chemical species involved in the petroleum cracking and refining, coal processing, polymerization chemistry, and a variety of biosynthetic pathways, amongst others. Therefore, the knowledge of these intermediates and their chemistry is of significance to both fundamental research and practical science. During the past century, much effort was devoted to outline the modern bonding theory for carbocations, which was largely prompted by investigations on the structure of the 2-norbornyl cation. This only apparently simple carbocation was found to adopt a symmetrical, bridged structure with a 3-center, 2-electron unit (much like the bonding in diborane), which implies the existence of hypercoordinated carbon atoms. Given this unique electronic structure, the 2-norbornyl cation, and carbocations with alike properties, are referred to as “non-classical”.
Spearheading the team, Dr. Roberta Properzi and her colleagues found that the symmetry of the 2-norbornyl cation can be broken by the generation of an asymmetric environment around the 3-center, 2-electron bond. Enzyme-like imidodiphosphorimidate (IDPi) catalysts are indeed able to recognize and transform substrates that can generate said intermediate, enabling highly enantioselective addition reaction to a carbocation that lacks traditional handles for noncovalent interactions. The research team describes their work in “Catalytic enantiocontrol over a non-classical carbocation” now published in Nature Chemistry.