Fullerene Dications and Trications as Initiators in the Gas-Phase “Ball-and-Chain” Polymerization of Allene and Propyne: Observation of a Remarkable Periodicity in Chain Growth with Allene

The chemistry initiated by C 60 x + (with x = 1, 2, and 3) in allene and propyne has been tracked in the gas phase. Reaction rate coefficients and product distributions were measured with the Selected-Ion Flow Tube (SIFT) technique operating at 294 ± 3 K and at a helium buffer-gas pressure of 0.35 ± 0.01 Torr. C 60 • + does not react with allene and propyne under SIFT conditions, but multiple addition was observed with C 60 2+ . Multiple addition was also observed in the reaction of propyne with C 60 3+, but allene reacted only by electron transfer with this cation. Up to 16 molecules of allene were observed to add to C 60 2+ with a remarkable periodicity in reactivity: even-numbered adducts react approximately 10 times faster than odd-numbered adducts. Multi-collision induced dissociation (CID) experiments demonstrated that the observed multiple-adduct ions have a “ball-and-chain” structure. Mechanisms are proposed for the sequential addition reactions and for the formation of C 6 H 7 + and C 9 H 12 + which was seen to compete with multiple addition in the reactions of allene with C 60 2+ and of propyne with C 60 3+ . The multiple-addition reactions are proposed to occur by chain propagation. The periodicity in the rates of the reactions of allene with C 60 (allene) n 2+ is attributed to differences in charge distribution and stability associated with an alternating formation of acyclic and cyclic structures.