Observation of a Cu^II₂(μ‐1,2‐peroxo)/Cu^III₂(μ‐oxo)₂ Equilibrium and its Implications for Copper–Dioxygen Reactivity

Abstract

Synthesis of small-molecule Cu 2 O 2 adducts has provided insight into the related biological systems and their reactivity patterns including the interconversion of the Cu II 2 (mh 2 :h 2 -peroxo) and Cu III 2 (m-oxo) 2 isomers. In this study, absorption spectroscopy, kinetics, and resonance Raman data show that the oxygenated product of [(BQPA)Cu I ] + initially yields an "end-on peroxo" species, that subsequently converts to the thermodynamically more stable "bis-m-oxo" isomer (K eq = 3.2 at À90 8C). Calibration of density functional theory calculations to these experimental data suggest that the electrophilic reactivity previously ascribed to end-on peroxo species is in fact a result of an accessible bis-m-oxo isomer, an electrophilic Cu 2 O 2 isomer in contrast to the nucleophilic reactivity of binuclear Cu II end-on peroxo species. This study is the first report of the interconversion of an end-on peroxo to bis-m-oxo species in transition metal-dioxygen chemistry.[**] These studies were supported by the NIH (DK031450 to E.I.S.;GM60353 to K.D.K.; postdoctoral fellowship GM085914 to M.K.E.).

Copper–Oxygen Complexes Revisited: Structures, Spectroscopy, and Reactivity

“…An equilibrium between ( trans -1,2-peroxo)- and bis( μ -oxo)dicopper cores was reported, 345 with possible implications for understanding novel reactivity ascribed to the former. 346 Following previous studies of the oxygenation of [( L40d )Cu]-PF 6 in EtCN, 349,350 it was found that oxygenation of its B(C 6 F 5 ) 4 − salt in THF initially yielded UV – vis spectra consistent with ( trans -1,2-peroxo)dicopper species but then evolved to a final spectrum that also contained features indicative of the bis( μ -oxo)dicopper core.…”

“…346 It was proposed that a bis( μ -oxo)dicopper isomer was energetically inaccessible; however, this was challenged using the calibrated DFT method, which suggests that the phenolate oxidation might actually be performed by a bis( μ -oxo)dicopper isomer. 345 …”

“…Proposed equilibrium between C i (left) and C 1 (right) isomers of ( trans -1,2-peroxo)dicopper complexes with bis( μ -oxo)dicopper isomer (ref 345). …”

Hand in Hand: Experimental and Theoretical Investigations into the Reactions of Copper(I) Mono‐ and Bis(guanidine) Complexes with Dioxygen

“…Historically, a trans ‐µ‐peroxido of type T P was discovered earlier by Karlin et al but it has not been found in biological systems , . Recently, it was shown that this species exists in an equilibrium with the O core . An equilibrium between the isomeric P species has not yet been established.…”

Dioxygen Activation by a Macrocyclic Copper Complex Leads to a Cu2O2 Core with Unexpected Structure and Reactivity

“…[5] Particularly relevant are our recent findings in the stabilization of mononuclear end-on LCu II (O 2 •− ) species ( E S ) making use of electron-rich TMPA derivatives [6] or by H-bonding interactions, [7] and our recent reports on the first examples of end-on peroxo-dicopper(II) intermediates ( E P ) that undergo reversible O–O cleavage via formation of dicopper(III) bis(μ-oxo) species ( O ). [8] These results show that even after many years of study, new Cu/O 2 reactivity patterns are still emerging.…”