Homogeneous and heterogenized copper(II) complexes as catechol oxidation catalysts

Two macroacyclic ligands represented as L-1 and L-2 with 3N(2)O and 5N donor atoms, respectively, have been synthesized by Schiff base condensation. They were subsequently grafted on a silica surface via covalent bonds. The organic ligands L, and L-2 as well as the heterogenized ligands L-1.SiO2 and L-2.SiO2 reacted with copper(II) leading to the formation of dinuclear copper(H) complexes. Catalytic oxidation of 3,5-di-t-butylcatechol (DTBC) by dioxygen was studied using as catalysts the homogeneous Cu-2(L-1) and Cu-2(L-2) and the heterogenized Cu-2(L-1).SiO2 and Cu-2(L-2).SiO2 complexes. These complexes were found to be very effective catalysts for DTBC oxidation producing mainly 3,5-di-t-butylquinone (DTBQ). During the catalytic process the formation of an o-semiquinone radical has also been confirmed. The immobilized on modified silica surface copper(II) complexes gave significantly higher DTBC conversion than the homogeneous copper(II) complexes. (C) 2002 Elsevier Science B.V. All rights reserved.