Bifunctional Carbenium Dications as Metal-Free Catalysts for the Reduction of Oxygen

The development of catalysts for the oxygen reduction reaction is a coveted objective of relevance to energy research. This study describes a metal-free approach to catalyzing the reduction of O 2 into H 2 O 2, based on the use of redox-active carbenium species. The most active catalysts uncovered by these studies are the bifunctional dications 1,8-bis(xanthylium)-biphenylene ([ 3 ] 2+ ) and 4,5-bis(xanthylium)-9,9-dimethylxanthene ([ 4 ] 2+ ) which promote the reaction when in the presence of decamethylferrocene and methanesulfonic acid. Electrochemical studies carried out with [ 4 ] 2+ suggest the intermediacy of an organic peroxide that, upon protonation, converts back into the starting dication while also releasing H 2 O 2 . Kinetic studies point to the second protonation event as being rate-determining.