On the origins of the mechanistic variants in the thermal reactions of Sx+ (x = 1-3) with benzene

Carbon-Atom Exchange between [MC2]+ (M = Os and Ir) and Methane: on the Thermodynamic and Dynamic Aspects

Gas-phase reactions of [OsC2]+ and [IrC2]+ with methane at ambient temperature have been studied using quadrupole-ion trap mass spectrometry combined with quantum chemical calculations. Both [OsC2]+ and [IrC2]+ undergo carbon-atom exchange reactions with methane. The associated mechanisms for the two systems are found to be similar. The differences in the rates of carbon isotope exchange reactions of methane with [MC2]+ (M = Os and Ir) are explained by several factors like the energy barrier for the initial H3C-H bond breaking processes, the molecular dynamics, orbital interactions, and the H-binding energies of the pivotal steps. Besides, the number of participating valence orbitals might be one of the keys to regulate the rate in the key step. The present findings may provide useful ideas and inspiration for designing similar processes.

Infrared Spectroscopy of (Benzene-H2S-Xn)+, X = H2O (n = 1 and 2) and CH3OH (n = 1), Radical Cation Clusters: Microsolvation Effects on the S-π Hemibond

An unconventional covalent bond in which three electrons are shared by two centers is called hemibond. Hemibond formation frequently competes with proton transfer (or ionic hydrogen bond formation), but there have been a few experimental reports on such competition. In the present study, we focus on the (benzene-H₂S)⁺ radical cation cluster, which is a model system of the S-π hemibond. The stability of the S-π hemibond to the microsolvation by water and methanol is explored with infrared spectroscopy of (benzene-H₂S-X_n)⁺, X = H₂O (n = 1 and 2) and CH₃OH (n = 1), clusters. We also perform energy-optimization and vibrational simulations of (benzene-H₂S-X_n)⁺. By comparison among the observed and simulated spectra, we determine the intermolecular binding motifs in (benzene-H₂S-X_n)⁺. While the S-π hemibonded isomer is exclusively populated in (benzene-H₂S-H₂O)⁺, both the hemibonded and proton-transferred isomers coexist in [benzene-H₂S-(H₂O)₂]⁺ and (benzene-H₂S-CH₃OH)⁺. Breaking of the S-π hemibond by the microsolvation is observed, and its solvent and cluster size dependence is interpreted by the proton affinity and the coordination property of the solvent moiety.