Copper-dioxygen complexes and their roles in biomimetic oxidation reactions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 104

propose that the ligand hydroxylation involves intramolecular C-H bond
activation by an unobserved intermediate, based on

the results of mechanistic studies.

More recently, Itoh and co-workers 110 reported on similar benzylic
hydroxylation chemistry using an analogous ligand, N-ethyl-N-[2-(2-
pyridyl)ethyl]-2-phenylethylamine. This system employs a bidentate ligand
instead of the tridentate PY2Phe, which forms the
instead of a intermediate, presumably because
bidentate ligands help stabilize the formally Cu(III) centers of the
core due to the fact that transition metal compounds prefer