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

Daliran, Saba, Santiago-Portillo, Andrea, Navalón, Sergio, Oveisi, Ali Reza, Álvaro, Mercedes, Ghorbani-Vaghei, Ramin, Azarifar, Davood, García, Hermenegildo
Journal of colloid and interface science 2018 v.532 pp. 700-710
Fourier transform infrared spectroscopy, benzyl alcohol, catalysts, chemical bonding, copper, electron paramagnetic resonance spectroscopy, ethylbenzene, filtration, hydroxybenzaldehyde, ligands, nuclear magnetic resonance spectroscopy, oxidation
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.