Nucleophilic reactivity of a copper(II)-hydroperoxo complex

Bohee Kim,Takehiro Ohta,Jaeheung Cho,Donghyun Jeong

doi:10.1038/s42004-019-0187-3

Bohee Kim, Takehiro Ohta + Show 2 more

Open Access

https://doi.org/10.1038/s42004-019-0187-3

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Abstract

Copper(II)-hydroperoxo species are often detected as key intermediates in metalloenzymes and biomimetic compounds containing copper. However, the only reactivity has previously been observed for the copper(II)-hydroperoxo complexes is electrophilic, occurring through O-O bond cleavage. Here we report that a mononuclear end-on copper(II)-hydroperoxo complex, which has been successfully characterized by various physicochemical methods including UV-vis, rRaman, CSI-MS and EPR, is a reactive oxidant that utilizes a nucleophilic mechanism. In addition, DFT calculations fully support the electronic structure of this complex as a copper(II)-hydroperoxo complex with trigonal bipyramidal coordination geometry. A positive Hammett ρ value (2.0(3)) is observed in the reaction of copper(II)-hydroperoxo complex with para-substituted acyl chlorides, which clearly indicates nucleophilic character for the copper(II)-hydroperoxo complex. The copper(II)-hydroperoxo complex is an especially reactive oxidant in aldehyde deformylation with 2-PPA and CCA relative to the other metal-bound reactive oxygen species reported so far. The observation of nucleophilic reactivity for a copper(II)-hydroperoxo species expands the known chemistry of metal-reactive oxygen species.

Highlights

Copper(II)-hydroperoxo species are often detected as key intermediates in metalloenzymes and biomimetic compounds containing copper
In peptidylglycineα-hydroxylating monooxygenase (PHM) and dopamine-βmonooxygenase (DβM), it has been proposed that Cu(II)hydroperoxo species were converted to Cu(II)-oxyl radicals and water after electron and proton transfers[3,4,5]
We report the nucleophilic reactivity of the Cu(II)hydroperoxo complex, [Cu(iPr3-tren)(OOH)]+ (1, iPr3-tren = tris[2-(isopropylamino)ethyl]amine), which we find is capable of oxidation of organic carbonyl compounds directly. 1 was successfully characterized by various spectroscopic methods such as UV-vis, resonance Raman, and electron paramagnetic resonance (EPR) spectroscopy together with cold spray ionization mass spectrometry (CSI-MS)

Summary

Results

The optimized structure of 1 reveals the trigonal bipyramidal geometry whose axial site is occupied by the hydroperoxo group in the manner of end-on replacing an acetonitrile of [Cu(iPr3-tren) (CH3CN)]2+ (Fig. 2, and see Supplementary Table 4). This result is in agreement with the result of EPR spectroscopy described above.

H CI F CH3

Discussion

Methods