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Encapsulation of Tricopper Cluster in a Protein-like Cavitand Enables Facile Redox Processes from CuICuICuI to CuIICuIICuII States
Preprints are manuscripts made publicly available before they have been submitted for formal peer review and publication. They might contain new research findings or data. Preprints can be a draft or final version of an author's research but must not have been accepted for publication at the time of submission.
submitted on 31.08.2020 and posted on 01.09.2020by Shiyu Zhang, Weiyao Zhang, Curtis Moore
One-pot reaction of tris(2-aminoethyl)amine (TREN), [CuI
(MeCN)4]PF6, and paraformaldehyde affords a mixedvalent [TREN4CuIICuICuI
(3-OH)](PF6)3 complex. The macrocyclic azacryptand TREN4 contains four TREN motifs, three of
which provide a bowl-shape binding pocket for the [Cu3(3-OH)]3+ core. The fourth TREN caps on top of the tricopper cluster to
form a cavitand, imposing conformational constraints and preventing solvent interaction. Contrasting the limited redox capability of
synthetic tricopper complexes reported so far, [TREN4CuIICuICuI
(3-OH)](PF6)3 exhibits several reversible single-electron redox
events. The distinct electrochemical behaviors of [TREN4CuIICuICuI
(3-OH)](PF6)3 and its solvent-exposed analog
(3-O)](PF6)4 suggest that isolation of tricopper core in a protein-like cavitand enables facile electron transfer,
allowing potential application of synthetic tricopper complexes as redox catalysts. Indeed, the fully reduced [TREN4CuICuICuI
OH)](PF6)2 can reduce O2 under acidic conditions. The geometric constraints provided by the cavitand are reminiscent of Nature’s
multicopper oxidases (MCOs). For the first time, a synthetic tricopper cluster was isolated and fully characterized at CuICuICuI
(4b), and CuIICuIICuI
(4c) state, providing structural and spectroscopic models for many intermediates in MCOs.
Fast electron transfer rates (105
- 106 M −1
) were observed for both CuICuICuI
redox couples, approaching the rapid electron transfer rates of copper sites in MCO.