Gas-phase reactions of fullerene cations C 60x+ ( x = 1–3) with pyridine and pyrrole: formation of “ball-and-chain” and “spindle” isomers and their interconversion

Abstract

The chemistry of buckminsterfullerene cations with charge states of +1, +2, and +3 has been investigated with two nitrogen heterocycles, pyridine and pyrrole, in the gas phase at room temperature in helium buffer gas at 0.35 Torr using the selected ion flow tube (SIFT) technique. Adduct formation was observed with pyridine for all three charge states of C 60 x+ , although electron transfer leading to charge separation was the predominant channel with C 60 ·3+. The number of pyridine molecules sequentially added was equal to the number of charges on C 60 x+ . Equilibrium was achieved for the addition of pyridine to C 60 ·+ and a bond dissociation enthalpy of 19.5 kcal mol −1 was deduced from the measured equilibrium constant. The structures of the derivatized C 60 cations was explored by multicollision-induced dissociation in mixed He/Ar collision gas. All observed dissociations were heterolytic. With the multiply derivatized C 60 cations evidence was obtained for both a kinetically favored “ball-and-chain”-like structure and a thermodynamically favored “spindle”-like structure. Experiments with doubly derivatized C 60 2+ indicated the occurrence of a rapid conversion of the ball-and-chain to the spindlelike structure in a bimolecular reaction with pyridine. Only charge-separation reactions driven by electron transfer were observed with pyrrole. The results for the two nitrogen heterocycles are compared with those obtained under similar operating conditions for ammonia and several aliphatic amines. A correlation is presented between the observed reactivity of C 60 x+ and the proton affinity of the adduct molecule.