Cerium photocatalysis conquers light hydrocarbon chemistry

Reactions that replace carbon-hydrogen bonds with other chemical moieties, called C–H activation reactions, have multiplied in recent years, seemingly spreading to every corner of chemical space. Yet a general method for the activation of light hydrocarbons has hovered just out of chemists’ reach. Because gaseous molecules like methane and ethane are insoluble in most solvents and contain notoriously inert C–H bonds, researchers have resorted to high pressures and temperatures to get the compounds to react with transition-metal catalysts. Now, an approach developed in Zhiwei Zuo’s lab at ShanghaiTech University leverages photocatalysis to promote the C–H functionalization of light alkanes under ambient conditions, except for methane, which required somewhat elevated pressures (Science 2018, DOI: 10.1126/science.aat9750). Using a cheap cerium catalyst and an alcohol hydrogen atom transfer catalyst lit by blue light-emitting diodes, the researchers performed C–H aminations, alkylations, and arylations of light alkanes up to cyclohexane. This work offers an economical way to upgrade feedstock alkanes into commodity compounds, Zuo says, adding that the team is collaborating with experts at Shell to develop additional valuable transformations. The researchers also demonstrated their method in a continuous-flow setup with 10 microreactors, showing that the reaction may be scalable.