Oxidant types in copper–dioxygen chemistry: the ligand coordination defines the Cu n -O2 structure and subsequent reactivity

Abstract

The considerable recent advances in copper-dioxygen coordination chemistry demonstrate the existence of a variety of dioxygen-derived Cu(n)-O(2) complexes, forming a basis for discussion of alternate oxidant types in copper chemistry and biochemistry. Peroxo complexes may react as nucleophilic reagents, and several types of electrophilic mono- or dicopper (hydro)peroxides exist. Side-on peroxo-dicopper(II) species effect aromatic hydroxylations, including phenolic substrates, in model systems and in the enzyme tyrosinase. Bis-micro-oxo-dicopper(III) entities are capable of hydrogen-atom abstraction reactions, or atom transfer to phosphines and sulfides. The scope and mechanisms of mononuclear Cu(II) superoxides or peroxides are yet to be established, but may be relevant to monooxygenases like peptidylglycine alpha-hydroxylating monooxygenase.

Theoretical Models on the Cu2O2 Torture Track: Mechanistic Implications for Oxytyrosinase and Small-Molecule Analogues

“…12,13,17,36 In particular, end-on peroxo species have been characterized as basic (subject to protonation to generate hydrogen peroxide) and nucleophilic (reactive with acylating agents) but not particularly electrophilic (no oxidation of phosphines to phosphine oxides). Side-on peroxo compounds, by contrast, fail to exhibit basic character and enhance the electrophilicity of the bound O 2 fragment, as judged by their abilities to abstract H atoms from good donors, oxidize phosphines to phosphine oxides, and hydroxylate aromatic rings both intra-and intermolecularly.…”

Theoretical Characterization of End-On and Side-On Peroxide Coordination in Ligated Cu2O2 Models

“…12,19 Best characterized experimentally (because they have been observed for many different supporting ligand sets) are the side-on µ-η 2 :η 2 peroxo and the bis(µ-oxo). The trans end-on µ-η 1 :η 1 peroxo motif was first described by Jacobson et al 20 This binding mode is preferred when the copper atoms are supported by tripodal tetradentate ligands, [21][22][23][24][25] although when such ligands become too sterically demanding for trigonal bipyramidal coordination of copper a preference for the bis(µ-oxo) motif with concomitant loss of two ligand-copper interactions has been documented. 26 Only rare examples of the other three cases shown in Figure 1 have been documented or proposed.…”

Calix[6]tren and copper(II): A third generation of funnel complexes on the way to redox calix-zymes

“…A good chemical model for metalloenzymes is a key to the understanding of the fundamental mechanisms involved in the catalytic cycle and to the design of efficient and selective new tools for the synthetic chemist. Most classical models, however, irreversibly lead to dinuclear species because of the propensity of reactive cupric species to undergo dimerization (7)(8)(9)(10). Trying to gain insights into the chemical and redox specificity (11)(12)(13)(14)(15) resulting from the proteic environment of mono-copper sites, we have developed a supramolecular system that mimics not only the polyhistidine binding core but also the hydrophobic pocket that controls the second coordination sphere of the metal and its binding to an exogenous molecule.…”