Substrate and Lewis Acid Coordination Promote O–O Bond Cleavage of an Unreactive L₂Cu^II₂(O₂^2–) Species to Form L₂Cu^III₂(O)₂ Cores with Enhanced Oxidative Reactivity

Abstract

Copper-dependent metalloenzymes are widespread throughout metabolic pathways, coupling the reduction of O2 with the oxidation of organic substrates. Small-molecule synthetic analogs are useful platforms to generate L/Cu/O2 species that reproduce the structural, spectroscopic, and reactive properties of some copper-/O2-dependent enzymes. Landmark studies have shown that the conversion between dicopper(II)-peroxo species (L2CuII2(O22−) either side-on peroxo, SP, or end-on trans-peroxo, TP) and dicopper(III)-bis(μ-oxo) (L2CuIII2(O2−)2:O) can be controlled through ligand design, reaction conditions (temperature, solvent, and counteranion), or substrate coordination. We recently published (J. Am. Chem. Soc. 2012, 134, 8513, DOI: 10.1021/ja300674m) the crystal structure of an unusual SP species [(MeAN)2CuII2(O22−)]2+ (SPMeAN, MeAN: N-methyl-N,N-bis[3-(dimethylamino)propyl]amine) that featured an elongated O–O bond but did not lead to O–O cleavage or reactivity toward external substrates. Herein, we report that SPMeAN can be activated to generate OMeAN and perform the oxidation of external substrates by two complementary strategies: (i) coordination of substituted sodium phenolates to form the substrate-bound OMeAN-RPhO− species that leads to ortho-hydroxylation in a tyrosinase-like fashion and (ii) addition of stoichiometric amounts (1 or 2 equiv) of Lewis acids (LA’s) to form an unprecedented series of O-type species (OMeAN-LA) able to oxidize C–H and O–H bonds. Spectroscopic, computational, and mechanistic studies emphasize the unique plasticity of the SPMeAN core, which combines the assembly of exogenous reagents in the primary (phenolates) and secondary (Lewis acids association to the MeAN ligand) coordination spheres with O–O cleavage. These findings are reminiscent of the strategy followed by several metalloproteins and highlight the possible implication of O-type species in copper-/dioxygen-dependent enzymes such as tyrosinase (Ty) and particulate methane monooxygenase (pMMO).

A comparative test of different density functionals for calculations of NH3-SCR over Cu-Chabazite

“…Even though this is an unusual oxidation state of Cu, it has been identified earlier for similar Cu 2 O 2 motifs in enzymatic catalysts. 23,55,56 To investigate the effect of the incorporation of vdW interaction, the oxidation of Cu with oxygen in the gas phase is investigated using the BEEF and PBE-cx functionals. The spatial confinement in the zeolite cages is expected to give substantial vdW interactions with the Cu-complexes.…”

Modulation of a μ-1,2-Peroxo Dicopper(II) Intermediate by Strong Interaction with Alkali Metal Ions

“…Lewis acid adducts of peroxo complex [(TMC)­Fe III (O 2 )] + (left) and reversible O–O cleavage interconverting S P and O cores in Cu 2 O 2 intermediates mediated by the Lewis acid Sc 3+ (right) …”

Effect of Al-distribution on oxygen activation over Cu–CHA

“…Binuclear copper sites play an important role in enzymatic reactions as copper containing proteins are known to facilitate a range of zero-, two-or four-electron processes involving oxygen. [1][2][3][4] The nature of the active binuclear centers has been investigated extensively and characterized as being either coupled or non-coupled, depending on the distance between the metal sites. 2 Using model complexes, it has demonstrated that the Cu-Cu distance can be used as a design parameter to stabilize oxygen in different structural and electronic configurations.…”