Dicopper Dioxygenase Model Immobilized in Mesoporous Silica Nanoparticles for Toluene Oxidation: A Mechanism to Harness Both O Atoms of O₂ for Catalysis

Recently, we have reported on a dicopper system (Cu^III(μ-O)₂Cu^III complex immobilized in mesoporous silica nanoparticles) that can mediate the catalytic conversion of toluene into benzaldehyde by O₂, in which the oxidizing power of both O atoms is harnessed for catalytic turnover. This is the first example of a Cu^III(μ-O)₂Cu^III complex capable of functioning like a "dioxygenase" in hydrocarbon oxidation. We have undertaken a mechanistic study to clarify how this catalytic conversion is accomplished without the input of sacrificial reductants. While the first O atom in the Cu^III(μ-O)₂Cu^III complex can actively insert into a C-H bond, the second O atom left in the Cu^II(μ-O)Cu^II complex is inert. We show that a second molecule of O₂ is involved in activating the dicopper catalyst, forming an O₂ complex with the Cu^II(μ-O)Cu^II intermediate to give a species with the [Cu₂O₃]²⁺ core, which then mediates the transfer of the remaining O atom of the original O₂ molecule to the organic substrate to complete the catalytic turnover. The study offers a mechanistically characterized analogue of the heterogeneous metal oxide catalyst that oxidizes organic substrates with the lattice oxygens by the Mars-van-Krevelen (MvK) mechanism at significantly higher temperatures.