Influence of the organic linker substituent on the catalytic activity of MIL-101(Cr) for the oxidative coupling of benzylamines to imines

Abstract

MIL-101(Cr) having substituents at the terephthalate linker (X = H, NO₂, SO₃H, Cl, CH₃ and NH₂) promotes the aerobic oxidation of benzylamines to the corresponding N-benzylidene benzylamines at different rates. MIL-101(Cr)–NO₂ was the most active catalyst, about 6-fold more active than the parent MIL-101(Cr). MIL-101(Cr)–NO₂ does not deactivate significantly upon five consecutive reuses, does not leach the metal to the solution and maintains its crystallinity. MIL-101(Cr)–NO₂ is active for a wide range of benzylamines including para-substituted, heterocyclic benzylamines and di- and tribenzylamines.