Tunable Porphyrin Cage Based on Designed Electric Field for Methane Capture and Oxidation.

Methane is a generic chemical feedstock, and its conversion to methanol can provide an alternative fuel. We herein provide a first-principles-based strategy for designing a catalyst that operates in a synchronized catalytic cycle and efficiently converts methane into methanol. In so doing, we designed an earlier, experimentally synthesized, porphyrin-based supramolecular cage based on a designed local electric field (D-LEF) by strategically substituting charged groups. We show that the negatively charged substitutions at the porphyrin destabilize the transition state, which, in turn, inhibits the active oxidant formation (Fe═O) as well as the methanol production. In contrast, the positively charged substitution efficiently forms the active oxidant cage and catalyzes the methanol formation. As such, we propose that D-LEF acts as a switch for the methane-to-methanol conversion, and one can readily enhance or inhibit it by switching between different charge states of the molecular cages. As such, this conceptual study will guide experimentalists in designing highly efficient, switchable supramolecular cages.