Design of a bio-inspired copper (II) Schiff base complex grafted in mesoporous silica for catalytic oxidation

Abstract

Controlled grafting of a copper (II) complex with a Schiff base ligand (LA=N-(salicylaldimine)-(N′-propyltrimethoxysilane)-diethylenetriamine) on a mesoporous MCM-41 type of silica (LUS) was accomplished using a pattering technique to allow a homogeneous distribution of isolated copper sites on the solid using trimethylsilyl groups as dispersing function. XRD patterns suggest that the final material LUS-CuLA exhibits a well-ordered 2D hexagonal structure. Elemental analysis, solid UV–Vis and EPR spectroscopies indicate that the copper (II) coordination sphere is most likely of a 3N1O type with an additional acetate ion as a ligand. Almost all the Cu(II) species grafted on the solid were EPR active (2.6wt% active species for 2.8wt% total copper measured from ICP-MS analysis) confirming the presence of monomeric copper species. Preliminary catalytic tests for phenol hydroxylation show that the supported system presents similar activity as the molecular analogue.