Arylation of [60]fullerene via electrophilic aromatic substitution involving the electrophile C60Cl6: frontside nucleophilic substitution of fullerenes

Abstract

Reaction of C₆₀Cl₆ and ferric chloride with aromatic compounds gives the corresponding C_s-symmetric aryl derivatives C₆₀Ar₅Cl, where Ar = phenyl, tolyl, anisyl, tert-butylphenyl, fluorophenyl, trimethylsilylphenyl and thienyl. The derivatives arising from exclusive para substitution in anisole and fluorobenzene, together with C₆₀(4-FC₆H₄)₅H have been isolated and fully characterised. Toluene undergoes substitution in the ortho as well as the para position. Traces of octaaryl derivatives are obtained in the reaction with toluene and anisole. The steric bulk of the chlorofullerene (the largest electrophile known) accounts for the failure to achieve substitution in mesitylene and the abnormal deprotonation rather than desilylation in the reaction with trimethylsilylbenzene. Protiodesilylation of the trimethylsilylphenyl derivative was achieved by reaction with acid. With triphenylphosphine, C₆₀Ar₅Cl compounds react to give C₆₀Ar₅H and with toluene/FeCl₃, C₆₀Ph₅Cl gives C₆₀Ph₅tolyl. C₆₀(4-FC₆H₄)₅H showed a marked tendency to acquire oxygen, suggesting that this oxygenation is facilitated by electron withdrawal. FAB mass spectrometry of C₆₀(4-FC₆H₄)₅H, C₆₀Ph₅Cl, C₆₀Ph₅H and also of C₇₀Ph₁₀ shows addition of up to 9C₂ fragments in each case; this parallels two previous reports of C₂ addition during FAB mass spectrometry. The replacement of chlorine by aryl groups at the same site indicates that frontside nucleophilic substitution on the cage must occur, involving a cationic fullerene intermediate.