Isolable fluorinated triphenylmethyl cation salts of [HCB11Cl11]−: demonstration of remarkable hydride affinity

Abstract

Significantly fluorinated triarylmethyl cations have long attracted attention as potentially accessible highly reactive carbocations, but their isolation in a convenient form has proved elusive. We show that abstraction of chloride with a cationic silylium reagent leads to the facile formation of di-, tetra-, and hexafluorinated trityl cations, which could be isolated as analytically pure salts with the [HCB₁₁Cl₁₁]⁻ counterion and are compatible with (halo)arene solvents. The F₆Tr⁺ cation carrying six meta-F substituents was computationally predicted to possess up to 20% higher hydride affinity than the parent triphenylmethyl cation Tr⁺. We report that indeed F₆Tr⁺ displays reactivity unmatched by Tr⁺. F₆Tr⁺ at ambient temperature abstracts hydrides from the C–H bonds in tetraethylsilane, mesitylene, methylcyclohexane, and catalyzes Friedel–Crafts alkylation of arenes with ethylene, while Tr⁺ does none of these.