Thermodynamics of a μ-oxo Dicopper(II) Complex for Hydrogen Atom Abstraction

Abstract

The mono-μ-hydroxo complex {[Cu(tmpa)]-(μ-OH)} (1) can undergo reversible deprotonation at -30 °C to yield {[Cu(tmpa)]-(μ-O)} (2). This species is basic with a pK of 24.3. 2 is competent for concerted proton-electron transfer from TEMPOH, but is an intrinsically poor hydrogen atom abstractor (BDFE(OH) of 77.2 kcal/mol) based on kinetic and thermodynamic analyses. Nonetheless, DFT calculations experimentally calibrated against 2 reveal that [CuO] is likely thermodynamically viable in copper-dependent methane monoxygenase enzymes.

Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function

“…Experiments found to be consistent with this result were that the complex could react with substrates containing weak C–H and O–H bonds (cyclohexadiene and TEMPO-H), giving the products benzene and TEMPO, respectively (Scheme 20). 811 While very strong C–H bonds, such as methane, could not be oxidized, this is the first indepth study obtaining thermodynamic parameters relevant to oxidation by a [Cu 2 O] 2+ species.…”

“…Most recently, Kieber-Emmons and co-workers 811 published on the thermodynamic parameters of hydrogen-atom-transfer reactivity by a model [Cu 2 O] 2+ complex. Titration of a structurally characterized ( μ -hydroxo)dicopper(II) complex bearing the TMPA ligand with the base 1,8- diazabicyclo[5.4.0]undec-7-ene (DBU) allowed for the determination of the pK a of the bound hydroxide ligand (pK a = 24.3 ± 1.9 in MeCN).…”

Structure and Reactivity of Copper Complexes Supported by a Bulky Tripodal N4 Ligand: Copper(I)/Dioxygen Reactivity and Formation of a Hydroperoxide Copper(II) Complex

“…Kieber‐Emmons et al recently reported the reaction of a dicopper(II)‐μ‐oxo adduct with TEMPOH, which resulted in the formation of a dicopper(I,II)‐μ‐hydroxo adduct via a concerted HAT mechanism. Kinetic study of the reaction revealed activation parameters of Δ H ‡ = 5.3 ± 2.8 kcal · mol –1 and Δ S ‡ = –44 ± 11 cal · K –1 · mol –1 , and a KIE (= k H / k D ) of 1.6 ± 0.3 …”

“…Thus, the O–H bond dissociation energy of 6 is suggested to be around 80 kcal · mol –1 . Of note, the O–H bond dissociation energy of Meyer's μ‐1,1‐hydroperoxo dicopper(II) complex was estimated as 72 kcal · mol –1[58] and Kieber‐Emmons's dicopper(I,II)‐ μ ‐hydroxo complex as 77.2 kcal · mol –1 …”

Bioinspired molecular catalysts for homogenous electrochemical activation of dioxygen

“…[17] They indeed showed that the reaction of the Mn III (OO -) with benzoic anhydride yielded the manganese-acylperoxo intermediate that gave a Mn V O resulting from the O-O heterolysis favoured by 1-methyl imidazole as an axial ligand (push effect). [16] and [28]).…”