Super Electron Donors Reduce Benzene

Benzene and other arenes are normally among the most challenging organic species to reduce. But not so for John A. Murphy of Scotland’s University of Strathclyde. Murphy and his colleagues have devised powerful new versions of neutral organic molecules that readily give away their electrons to reduce arenes and form reactive intermediates. These reagents, called super electron donors, are on track to become important synthetic tools for organic chemists. Few chemical reagents have the wherewithal to add an electron to a ground-state aromatic ring to form a radical anion. This type of electron transfer has traditionally required the most brutish of metal-based reducing agents, such as sodium metal dissolved in liquid ammonia. Murphy’s group originally discovered that a simple organic molecule, a bisimidazolylidene, was up to the task of reducing iodoarenes and arenesulfones. In Philadelphia, Murphy’s team reported that shining ultraviolet light on the bisimidazolylidene (shown, left) or a bispyridine analog (shown, right) promotes an electron to a higher energy level in the donor, generating the most powerful super electron donors to date (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201200084). The light-activated bisimidazolylidene reduces chlorobenzenes to nonchlorinated benzenes, usually a difficult reaction. And both light-activated super electron donors can ring-open diphenylcyclopropanes.