Catalysis in hydrogen-bridged radical cations.
Hydrogen-bridged radical cations (HBRCs) are an intriguing subclass of ion-molecule complexes. They may act as key intermediates of remarkable stability in both association and dissociation reactions of heteroatom-containing molecular ions. The H-bridge of such an HBRC can promote isomerization of its ionic component by H-transfer. Proton-transport catalysis (PTC) is a prime example. Here, a neutral molecule promotes the smooth transformation of an ion into its H-shift isomer by consecutive proton-transfer reactions. A celebrated case is the water catalyzed isomerization of CH(3)OH(•+) into its more stable distonic isomer (•)CH(2)OH(2)(+). Other early studies of  PTC also deal with catalyzing 1,2-H shifts in association reactions. This short review focuses on more recent combined experimental and computational studies of catalysis in HBRCs. Mechanisms involving both proton and H atom transfers have been proposed for a variety of systems of H-shift isomers.  It has also become clear that PTC is not confined to bimolecular reactions. It also features in the unimolecular chemistry of heteroatom- containing ions, which have a tendency to isomerize to HBRCs en route to their dissociation.
Laboratory Services Branch, Ministry of the Environment, 125 Resources Road, Toronto, ON, Canada, M9P 3V6. karl.jobst@ontario.ca
Karl J
KJ
Jobst
Moschoula A
MA
Trikoupis