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 O2 into H2O2, 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 H2O2. Kinetic studies point to the second protonation event as being rate-determining.氧还原反应（oxygen reduction reaction）催化剂的研发，是能源研究领域备受瞩目的重要目标。本研究报道了一种基于氧化还原活性碳鎓物种（redox-active carbenium species）的无金属催化路径，可将氧气（O₂）还原为过氧化氢（H₂O₂）。本研究筛选得到的活性最高的催化剂为双功能双阳离子：1,8-双(氧杂蒽鎓)-联苯撑([3]²⁺)与4,5-双(氧杂蒽鎓)-9,9-二甲基氧杂蒽([4]²⁺)，在十甲基二茂铁（decamethylferrocene）与甲磺酸（methanesulfonic acid）存在的条件下可催化该反应。针对[4]²⁺开展的电化学研究表明，反应过程中会生成有机过氧化物中间体；该中间体经质子化后，可重新转化为初始双阳离子并释放过氧化氢（H₂O₂）。动力学研究显示，第二次质子化步骤为该反应的决速步。