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

• Tridentate dicopper complex immobilized in mesoporous silica nanoparticle (MSN).
• The dicopper complex in MSN shows high activity and selectivity for toluene aliphatic oxidation.
• Room temperature oxidation to benzaldehyde without any benzoic acid formation.
• Gives consecutive reaction of toluene to benzyl alcohol and then to benzaldehyde.

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 ([{CuIIIImph}2(μ-O2−)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.

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