Bioinspired copper(I) complexes that exhibit monooxygenase and catechol dioxygenase activity.

ABSTRACT

New tripodal ligand L2 featuring three different pyridyl/imidazolyl-based N-donor units at a bridgehead C atom, from which one of the imidazolyl units is separated by a phenylene linker, was synthesized and investigated with regards to copper(I) complexation. The resulting complex [(L2)Cu]OTf (2(OTf)), the known complex [(L1)Cu]OTf (1(OTf); L1 differs from L2 in that it lacks the phenylene spacer) and [(L3)Cu]OTf (3(OTf)), prepared from a known chiral, tripodal, N-donor ligand featuring pyridyl, pyrazolyl, and imidazolyl donors, were tested as catalysts for the oxidation of sodium 2,4-di-tert-butylphenolate (NaDTBP) with O2. Indeed, they mediated NaDTBP oxidation to give mainly the corresponding catecholate and quinone (Q). None of the complexes 1(OTf), 2(OTf), and 3(OTf) is superior to the others, as yields were comparable and, if the presence of protons is guaranteed by concomitant addition of the phenol DTBP, the oxidation can also be performed catalytically. For all complexes stoichiometric oxidations under certain conditions (concentrated solutions, high NaDTBP content) were found to also generate products typical for metal-mediated intradiol cleavage of the catecholate with O2. As shown representatively for 1(OTf) this dioxygenation sets in at a later stage of the reaction. Initially a copper species responsible for the monooxygenation must form from 1(OTf)/NaDTBP/O2, and only thereafter is the copper species responsible for dioxygenation formed and consumes Q as substrate. Hence, under these circumstances complexes 1(OTf)-3(OTf) show both monooxygenase and catechol dioxygenase activity.