Structure-activity correlations in highly preorganized dicopper catechol oxidase model systems

New dicopper(II) complexes with pyrazolate-derived compartmental ligands that bear pyridyl or triazacyclononane chelate arms have been prepared and fully characterized, including several single-crystal X-ray analyses. These complexes complement a series of dicopper compounds with related pyrazolate ligands reported earlier. Modifications of the ligand scaffold are shown to control molecular features such as the (CuCu)-Cu-. . . separation and electronic and spectroscopic properties. Catecholase activity of the new complexes has been probed using 3,5-di-tert-butylcatechol (DTBC) as the test substrate, revealing Michaelis-Menten-type kinetics with drastic differences in activity for the assortment of complexes. Their common skeletal motif based on the pyrazolate bridge allowed us to deduce some relationship between activity and (CuCu)-Cu-. . . separation as well as Cu-II/Cu-I redox potentials. A dramatic effect of the buffer medium on reactivity has been observed.