Reaction of cyclopropenylium ions with the tert-butyl-C_(60) anion: carbocation-carbanion coordination vs salt formation

摘要

The reaction of the tert-butyl-C_(60) anion (t-BuC_((60)~-) with tricyclopropylcyclopropenylium ion and 1,2-dicyclopropyl-3(4-methylphenyl)cyclopropenylium ion underwent C-C covalent bond formation to give 1-tert-butyl-4-(2-cyclopropen-1-yl)-1,4-dihydro[6-]-fullerenes.The newly fromed C-C bond of these hydrocarbons was found to undergo reversible heterolysis in polar solvents to give the original ions.A more highly stabilized carbocation tris[1-(5-isopropyl-3,8-dimehtylazulenyl)]cyclopropenylium ion did not react with t-BuC_((60)~-), and a hydrocarbon with a salt structure was isolated as a solid.Tri-tert-butylcyclopropenylium ion, although less stable than the other cations,underwent no C-C bond formation with t-BuC_((60)~-),indicating that steric hindrance effectively suppresses carbocation-carbanion coordination.These redults provide a demonstration of a change in reactivity between t-BuC_((60)~-) and substituted cyclopropenylium ions toward C-C coordination,depending on the thermodynamic stability and steric crowding of the cation .