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

Abstract

Recently, we have reported on a dicopper system (Cu III (μ-O) 2 Cu III complex immobilized in mesoporous silica nanoparticles) that can mediate the catalytic conversion of toluene into benzaldehyde by O 2 , 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) 2 Cu 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) 2 Cu 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 O 2 is involved in activating the dicopper catalyst, forming an O 2 complex with the Cu II (μ-O)Cu II intermediate to give a species with the [Cu 2 O 3 ] 2+ core, which then mediates the transfer of the remaining O atom of the original O 2 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.

A nucleotide–copper(ii) complex possessing a monooxygenase-like catalytic function

“…Notably, the AMP/Cu 2+ complex exhibited optimal catalytic kinetics. Compared to the native monooxygenases and other synthetic monooxygenase-mimicking catalysts, [22][23][24][50][51][52][53][54] the following advantages of our catalyst are presented: (i) the synthesis of the catalysts and the modulation of their catalytic properties are straightforward and uncomplicated. (ii) The catalysts are environmentally friendly, exhibiting a greener alternative for catalytic processes.…”

“…20,21 The construction of these metallocenters is challenging, due to a stringent requirement for the spatial ligand distribution for clustering the metals, or the poor stability of the Cu + state under aerobic conditions or in a hydrous environment. A number of copper complexes have been reported for mimicking the monooxygenase activity under mild conditions, [22][23][24] while the synthetic procedures are complicated.…”

Making more with less: confinement effects for more sustainable chemical transformations

“…Another example highlighting oxidized hydrocarbons is the work of Liu et al on the oxidation of toluene to benzaldehyde using copper complexes immobilized on mesoporous silica. 77 The authors found that the mesopores had the perfect geometry to hold the metals in a position to stabilize O 2 -bridged dicopper species (Fig. 6), and the conversion was carried out at room temperature.…”