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.

Efficient Biomimetic Hydroxylation Catalysis with a Bis(pyrazolyl)imidazolylmethane Copper Peroxide Complex

“…Those species were also capable of oxygen activation. Earlier this year, they demonstrated the hydroxylation of 2,4‐di‐ tert‐ butylphenol (DTBP) to the corresponding quinone with this system 42. In parallel, Stack et al.…”

“…Earliert his year,t hey demonstrated the hydroxylationo f2 ,4-ditert-butylphenol( DTBP)t ot he corresponding quinonew itht his system. [42] In parallel,S tack et al showed that a P species with simplem ethylimidazoles could be stabilised at extremely low temperatures of À120 8Ca nd also displayed hydroxylationa ctivity. [43] Remarkably,t hese previous imidazolyl-containing systems did not show the catalytic activity demonstrated herein with the novel bis(pyrazolyl)imidazolylmethane ligand HC(3-tBuPz) 2 (1-MeIm) (L).…”

Investigation of 3d-transition metal acetates in the oxidation of substituted dioxolene and phenols

“…Bio-oxidation reactions have inspired the design of a library of metal complexes, which led to many successful functional models of enzymes over the past few decades [1][2][3][4][5]. These complexes have gained importance for their ability to shed insight on the mechanistic pathways of the original enzymes.…”