Copper tri- and tetraaza macrocyclic complexes were synthesized, encapsulated in zeolite-Y and characterized. The "neat" and encapsulated complexes exhibited good catalytic activity in the oxidation of ethylbenzene at 333 K, using tert-butyl hydroperoxide as the oxidant. Acetophenone was the major product though small amounts of o- and p-hydroxyacetophenones were also formed revealing that C-H bond activation takes place both at benzylic and aromatic ring carbon atoms. Ring hydroxylation was more over the "neat" complexes than over the encapsulated complexes. The differences in selectivity are attributed to the formation of different types of "active" copper-oxygen intermediates, such as side-on peroxide, bis-mu-oxo complexes and Cu-hydroperoxo species, in different proportions over the "neat" and encapsulated complexes. (C) 2003 Elsevier B.V. All rights reserved.