Introducing Supramolecular Interactions into Robust Bis(tetrabromocatecholate) Chelated Manganese(III) Systems and Biomimetic Catalytic Activity

This report deals with the syntheses, structures, supramolecular interactions, and biomimetic catalytic activity of three new manganese(III) complexes (1-3) containing the tetrabromocatechol ligand. Three different amines were used, with the goal of introducing their protonated species into the crystal lattice as counter cations for the robust bis(tetrabromocatecholate) chelated manganese(III) anionic species. All these systems present interesting noncovalent interactions in their crystal packing, including hydrogen bonding, halogen bonding, pi stacking and anion-pi interactions. The geometrical differences (octahedral vs square pyramidal) have been analyzed by means of DFT studies, revealing that the strong anion-pi interaction of pyridine with the complex anion compensates for the absence of one apical methanol molecule in 3. All of the complexes exhibited leveling catalytic activity for aerobic oxidation of 3,5di-tert-butylcatechol. DFT calculations support the formation of a stable complex-substrate intermediate through hydrogen bonding, thereby disclosing the origin of catecholase activity of these complex anions.