Thermal C-O coupling reactions of Ta methylene clusters [TanCH2]+ (n = 1, 4) with O2.

Cationic tantalum carbenes [TaCH2]+ and [Ta4CH2]+, products of thermal methane dehydrogenation, are collected and stored in a ring-electrode ion trap. In there, potential C-O coupling reactions are probed by exposing the tantalum carbenes to dioxygen in the presence of helium buffer gas, thereby facilitating reactions under-well defined multi-collision conditions at 300 K. Time-of-flight mass spectrometry determines the time-dependent reaction products and a kinetic analysis illustrates significantly different selectivities. The cationic tantalum atom and tetramer systems undergo coupling reactions, which may lead to the formation of value-added products from the oxidation of methane. In particular, the reaction of [Ta4CH2]+ with oxygen demonstrates an increased selectivity towards the formation of a formaldehyde equivalent.