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

Abstract

The chemistry initiated by C60 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. C60 ¥+ does not react with allene and propyne under SIFT conditions, but multiple addition was observed with C60 2+ . Multiple addition was also observed in the reaction of propyne with C60 3+ , but allene reacted only by electron transfer with this cation. Up to 16 molecules of allene were observed to add to C60 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 6H7 + and C9H12 + which was seen to compete with multiple addition in the reactions of allene with C60 2+ and of propyne with C60 3+ . The multiple- addition reactions are proposed to occur by chain propagation. The periodicity in the rates of the reactions of allene with C60(allene)n 2+ is attributed to differences in charge distribution and stability associated with an alternating