Cu(II)-Schiff base covalently anchored to MIL-125(Ti)-NH₂ as heterogeneous catalyst for oxidation reactions

MIL-125(Ti)-NH₂ has been modified by reaction of salicylaldehyde with the terephthalate amino groups to form a salicylideneimine that act as ligand of Cu²⁺. The success of the postsynthetic modification was assessed by FTIR spectroscopy of the MIL-125(Ti)-NH₂-Sal-Cu and by analysis by ¹H NMR spectroscopy of the organic linkers upon dissolution of MIL-125(Ti)-NH₂-Sal-Cu. In comparison with parent MIL-125(Ti)-NH₂ and MIL-125(Ti)-NH₂-Sal, that exhibit a poor activity, the presence of the Cu-Schiff base complex in MIL-125(Ti)-NH₂-Sal-Cu catalyst for the oxidation of 1-phenylethanol by tert-butylhydroperoxyde (TBHP, 3 eq.) increases notably the catalytic activity. Hot filtration test and reusability experiments confirm that the process is heterogeneous and that MIL-125(Ti)-NH₂-Sal-Cu is stable under the reaction conditions. Quenching studies and EPR spectra using N-^tbutylphenylnitrone indicate the generation of ^tBuOO and ^tBuO under the reaction conditions. The scope of MIL-125(Ti)-NH₂-Sal-Cu as oxidation catalyst by ^tBuOOH was studied for benzyl alcohol as well as alicyclic and aliphatic alcohols and ethylbenzene.