Superoxocopper(II) complexes are key intermediates in oxygen activation by a wide range of copper containing enzymes, and have been invoked as active oxidants in the catalytic cycles of numerous oxygenases and oxidases. For instance, they are widely accepted to be H-atom abstracting agents in the catalytic cycles of galactose oxidase (GO) and amine oxidase (AO), and evidence suggests they are the active oxidants in the substrate hydroxylation reactions promoted by peptidylglycine α-hydroxylating monooxygenase (PHM) and dopamine-β-monooxygenase (DβM). In the hope of gaining biological insight and harnessing such reactivity for synthetic purposes, significant effort has been expended in trying to study small molecule superoxocopper(II) complexes. These efforts are greatly hampered by the fact that such species, which are invariably formed as the initial products of reaction of copper(I) complexes with O2, tend to very unstable with respect to conversion to peroxo-bridged dicopper(II) complexes. The strategies that have yielded most success in trapping superoxocopper(II) complexes are the use of very low temperatures (≤ -85°C) and sterically encumbered ligands. The latter has been the most fruitful approach in terms of yielding stable species, but steric hindrance appears to stifle reactivity with substrates. We have addressed these issues by judicious incorporation of bulky substituents onto the widely studied tris(2-pyridylmethyl)amine (TMPA) ligand system. Copper(I) complexes of the resulting R3-TMPA ligands, [CuI(R3-TMPA)(NCCH3)]+, undergo reversible O2 binding to give solely end-on superoxocopper(II) complexes. Remarkably, partial formation of the superoxocopper(II) complexes can be observed even at ambient temperatures, and conversion to the corresponding peroxo-bridged dicopper(II) complexes is not observed under any conditions. Furthermore, although comparatively sluggish, our superoxocopper(II) complexes display a wide range of substrate reactivity. This, combined with their high stability, has allowed extensive mechanistic studies.

Stable end-on (η1) superoxocopper(II) complexes that display appreciable substrate reactivity

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.