Developing an efficient catalyst for controlled oxidation of small alkanes under ambient conditions†
The tricopper complex [CuICuICuI(7-N-Etppz)]1+, where 7-N-Etppz denotes the ligand 3,3′-(1,4-diazepane-1,4-diyl)bis[1-(4-ethyl piperazine-1-yl)propan-2-ol], is capable of mediating facile conversion of methane into methanol upon activation of the tricopper cluster by dioxygen and/or H2O2 at room temperature. This is the first molecular catalyst that can catalyze selective oxidation of methane to methanol without over-oxidation under ambient conditions. When this CuICuICuI tricopper complex is activated by dioxygen or H2O2, the tricopper cluster harnesses a “singlet oxene”, the strongest oxidant that could be used to accomplish facile O-atom insertion across a C–H bond. To elucidate the properties of this novel catalytic system, we examine here methane oxidation over a wider range of conditions and extend the study to other small alkanes, including components of natural gas. We illustrate how substrate solubility, substrate recognition and the amount of H2O2 used to drive the catalytic oxidation can affect the outcome of the turnover, including regiospecificity, product distributions and yields of substrate oxidation. These results will help in designing another generation of the catalyst to alleviate the limitations of the present system.