Gas-Phase Reactions of Atomic Gold Cations with Linear Alkanes (C2-C9)

To develop proper ionization methods for alkanes, the reactivity of bare or ligated transition metal ions toward alkanes has attracted increasing interests. In this study, the reactions of the gold cations with linear alkanes from ethane up to nonane (CnH2n+2, n = 2-9) under mild conditions have been characterized by mass spectrometry and density functional theory calculations. When reacting with Au+, small alkanes (n = 2-6) were confirmed to follow specific reaction channels of dehydrogenation for ethane and hydride transfer for others to generate product ions characteristic of the original alkanes, which indicates that Au+ can act as a reagent ion to ionize alkanes from ethane to n-hexane. Strong dependence of the chain length of alkanes was observed for the rate constants and reaction efficiencies. Extensive fragmentation took place for larger alkanes (n > 6). Theoretical results show that the fragmentation induced by the hydride transfer occurs after the release of AuH. Moreover, the fragmentation of n-heptane was successfully avoided when the reaction took place in a high-pressure reactor. This implies that Au+ is a potential reagent ion to ionize linear and even the branched alkanes.