Redox properties of a mononuclear copper(II)-superoxide complex

Area of Science:

• Bioinorganic Chemistry
• Coordination Chemistry
• Enzyme Mechanism

Background:

• Investigates a mononuclear copper(II) superoxide complex, (L)Cu(II)-OO(•), as a model for reactive intermediates in peptidylglycine α-hydroxylating monooxygenase (PHM) and dopamine β-monooxygenase (DβM).
• The tridentate ligand (L) is 1-(2-phenethyl)-5-[2-(2-pyridyl)ethyl]-1,5-diazacyclooctane.

Purpose of the Study:

• To examine the redox properties and reactivity of the (L)Cu(II)-OO(•) complex.
• To understand the reaction mechanisms with various one-electron reductants, phenols, phosphines, and sulfides.
• To compare its reactivity with other copper-superoxide complexes.

Main Methods:

• Electrochemical estimation of the reduction potential of the copper(II) superoxide complex.
• Reactivity studies with TEMPO-H, phenol derivatives, triphenylphosphine derivatives, and thioanisole.
• Analysis of reaction products and mechanisms, including Hammett analysis.

Main Results:

• The reduction potential of (L)Cu(II)-OO(•) was determined to be 0.19 ± 0.07 V vs SCE.
• Hydrogen atom transfer (HAT) occurred with TEMPO-H, forming LCu(II)-OOH.
• Phenol derivatives reacted via an acid-base mechanism, yielding phenolate adducts.
• Triphenylphosphine derivatives reacted via electrophilic ionic substitution (Hammett ρ = -4.3).
• Thioanisole reaction resulted in a copper(I) complex.
• Reactivity differs significantly from copper(II) complexes with tetradentate ligands.

Conclusions:

• The (L)Cu(II)-OO(•) complex exhibits unique reactivity patterns compared to other copper-superoxide models.
• The observed reactions provide insights into the mechanisms of copper-containing monooxygenase enzymes.
• The study highlights the influence of ligand environment on the reactivity of copper-superoxide species.