Gas-phase reactions of fullerene cations C-60(x+) (x=1-3) with pyrrolidineand piperidine: sequential reactions with C-60(+)

Results of selected-ion flow tube experiments are reported that explore the nucleophilic interaction of pyrrolidine and piperidine with C-60(+), C-60( 2+), C-60(3+) at 294 +/- 2 K in helium buffer gas at a pressure of 0.35 +/- 0.01 Torr. Two efficient sequential addition reactions were observed with C-60(+), in analogy with previous results obtained with acyclic amine nucle ophiles. Multicollision-induced dissociation experiments suggest the format ion and conversion of two isomers of the second adduct ion. As a first step C-N bond formation is proposed to occur with the C-60 cage with or without ring opening. Subsequent bonding may involve hydrogen bonding or, if ring opening occurs, further C-N bond formation at the terminus of the first sub stituent. Nucleophilic attack of C-60(2+) and C-60(3+) by pyrrolidine leads to ring cleavage and formation of C-60(NH3)(n+) (n = 2,3) accompanied by l oss of what is likely to be 1,3-butadiene. C-60(NH3)(n+) effectively donate s a proton to pyrrolidine. The ring-cleavage channel dominates competing ch annels leading to electron transfer and nucleophilic addition. However, rin g cleavage is not observed with piperidine which reacts with C-60(2+) and C -60(3+) exclusively by electron transfer because of its lower ionization po tential. Further reactions of the proton-transfer product lead to the forma tion of "mixed" adducts of the type (NH2)C-60(C4H8NH)(n+) (n = 1,2) that ma y involve two C-N bonds with the C-60 surface or, alternatively, proton bon ding to protonated aziridine.(C) 2000 Elsevier Science B.V.