Metal-Free Hydrogenations

Abstract

In a chemical first, an international research team has developed a metal-free reaction that hydrogenates aromatic rings to form cyclohexyl derivatives. The achievement could spark a broader range of applications for industrial hydrogenations, which are widely used for processing petroleum and foods. A metal-free aromatic hydrogenation is surprising, says team leader Douglas W. Stephan of the University of Toronto, because it’s exceedingly hard to overcome the additional stability a molecule gains from aromaticity, even with the best transition-metal catalysts. Stephan and his colleagues have done so by using a chemical construct known as a frustrated Lewis pair, which Stephan introduced in 2006. Lewis acid-base adducts are common in chemistry: An electron-deficient Lewis acid readily shares a Lewis base’s spare pair of electrons. However, when the Lewis acid and base have bulky substituents, their ability to form a close relationship is denied, causing the pair to become “frustrated.” But the pair ...