Site-Selective Supramolecular Complexation Activates Catalytic Ethane Oxidation by a Nitrido-Bridged Iron...

Development of supramolecular methods to further activate a highly reactive intermediate is a fascinating strategy to create novel potent catalysts for activation of inert chemicals. Herein, a supramolecular approach to enhance the oxidizing ability of a high-valent oxo species of a nitrido-bridged iron porphyrinoid dimer that is a known potent molecular catalyst for light alkane oxidation is reported. For this purpose, a nitrido-bridged dinuclear iron complex of porphyrin-phthalocyanine heterodimer 3⁵⁺ , which is connected through a fourfold rotaxane, was prepared. Heterodimer 3⁵⁺ catalyzed ethane oxidation in the presence of H₂ O₂ at a relatively low temperature. The site-selective complexation of 3⁵⁺ with an additional anionic porphyrin (TPPS^4- ) through π-π stacking and electrostatic interactions afforded a stable 1:1 complex. It was demonstrated that the supramolecular post-synthetic modification of 3⁵⁺ enhances its catalytic activity efficiently. Moreover, supramolecular conjugates achieved higher catalytic ethane oxidation activity than nitrido-bridged iron phthalocyanine dimer, which is the most potent iron-oxo-based molecular catalyst for light-alkane oxidation reported so far. Electrochemical measurements proved that the electronic perturbation from TPPS^4- to 3⁵⁺ enhanced the catalytic activity.