A room temperature catalyst for toluene aliphatic C-H bond oxidation: Tripodal tridentate copper complex immobilized in mesoporous silica

A tripodal tridentate copper(II) complex, CuImph (Imph = bis(4-imidazolyl methyl)benzylamine), is synthesized to mimic the active site of copper enzymes that mediate the oxidation of aliphatic C-H bonds under mild condition. By immobilizing the model complex in the nanochannels of functionalized mesoporous silica nanoparticles (MSNs), we observe the formation of a stable bis-μ-oxo species ([{Cu^IIIImph}₂(μ-O^2-)₂]²⁺) in the presence of dioxygen or air at ambient temperature. The dioxygen-activated CuImph@MSN samples show high reactivity and selectivity toward toluene aliphatic C-H bond oxidation, converting the toluene initially to benzyl alcohol and subsequently to benzaldehyde as the major product in a kinetic consecutive reaction. No evidence for benzoic acid is obtained, unlike the over-oxidation typically associated with present-day industrial processes operating at high temperatures. In addition, the process is self-sustaining without the requirement for a sacrificial reductant to drive the catalytic turnover. The catalyst can be fully recovered and re-used for several cycles without decay of activity.