Electron withdrawing ligands inhibit oxygen transport by Al+: temperature-dependent kinetics of AlO+/(O2)AlO+ + H2/CH4

Abstract

Al+ has been shown to enable the oxygen atom transfer (OAT) to convert methane to methanol at thermal energies through a unique, barrierless mechanism. Quantum chemical calculations suggested that the efficacy of methanol formation relative to other product channels could be tuned by the presence of electron-withdrawing or -donating groups. Here, the kinetics of AlO+, which has no electron-withdrawing group, and of (O2)AlO+, which includes an electron-withdrawing group, reacting with CH4 or with H2 are studied using a selected-ion flow tube apparatus. In all cases, AlO+ yields the OAT product (CH3OH or H2O) in addition to the hydrogen atom transfer (HAT) product, while (O2)AlO+ yields only the HAT product; the electron-withdrawing O2 group has inhibited oxidation as predicted.