Thermal and Near-Thermal Reactions of Pt+ and Au+ with Small Alkenes

The gas-phase reactions of Pt + and Au + with C 2 H 4, C 3 H 6, 1-C 4 H 8, cis -2-C 4 H 8, and trans -2−C 4 H 8 have been carried out under thermal and near-thermal conditions using a SIFT reactor and a drift cell. In all reactions examined here, Pt + exhibits dehydrogenation as the dominant primary product channel, but elimination of methane and ethene are observed in some systems in small amounts. Evidence for both allylic and vinylic activation of σ-bonds is observed. Observation of these bimolecular processes allow us to calculate D (Pt + · acetylene) > 49.76 ± 0.01 kcal/mol, D (Pt + ·allene) > 40.75 ± 0.01 kcal/mol, D (Pt + ·propyne) > 39.7 ± 0.1 kcal/mol and D (Pt + ·butadiene) > 29.01 ± 0.01 kcal/mol. Hydride abstraction is also observed as a minor product channel in the reactions of Pt + with C 3 H 6 and all three butene isomers. Secondary and tertiary reactions in the Pt + systems are limited to clustering reactions. Hydride abstraction is the only primary bimolecular pathway observed in the reactions of Au + with propene as well as the butene isomers. Au + forms adducts with both C 2 H 4 and C 3 H 6 in primary steps. Follow-on reactions are also observed in the Au + systems which include both bimolecular and clustering steps. Ion mobility experiments carried out using the drift cell indicate that both Pt + and Au + are in their ground states in the reactions described here. However, we show evidence that an Au + excited state can be populated under the appropriate ionizing conditions. Reduced zero-field mobilities for ground-state Pt + and Au + have been determined to be 20.6 ± 0.6 and 19.5 ± 0.5 cm 2 /V·s, respectively.