Revising C–H Oxidation

Shipping costs for natural gas limit its widespread feasibility as a fuel and are driving research toward selectively oxidizing methane—the primary compound in natural gas—to a more cheaply transported liquid, such as methanol. A proof-of-concept experiment from Roy A. Periana of Scripps Florida, William A. Goddard III of California Institute of Technology, and coworkers suggests that an alternative to traditional methane functionalization reactions might facilitate that conversion (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200802575). Established catalysts for functionalizing a methane C–H bond generate electrophilic intermediates and require acidic conditions that make it expensive to isolate methanol, Periana says. The team instead sought to functionalize nucleophilic intermediates, a strategy that's less established. The researchers formed a nucleophilic methyl intermediate by activating a methyl rhenium species with a base. By adding a second metal species, osmium tetroxide, they converted the nucleophile to methanol in quantitative yield at room temperature. Theory based on quantum mechanics indicates that the reaction proceeds through a cyclic transition state (shown). "This is an imaginative new direction in oxidation chemistry," says organometallic chemist James M. Mayer of the University of Washington.