Encapsulation of tricopper cluster in a synthetic cryptand enables facile redox processes from Cu^ICu^ICu^I to Cu^IICu^IICu^II states

Abstract

One-pot reaction of tris(2-aminoethyl)amine (TREN), [CuI(MeCN)4]PF6, and paraformaldehyde affords a mixed-valent [TREN4CuIICuICuI(μ3-OH)](PF6)3 complex. The macrocyclic azacryptand TREN4 contains four TREN motifs, three of which provide a bowl-shape binding pocket for...

Multiple Proton-Coupled Electron Transfers at a Tricopper Cluster: Modeling the Reductive Regeneration Process in Multicopper Oxidases

“…Recently, we reported the first tricopper complex that can access all four oxidation states from II,II,II to I,I,I. 22 The tricopper cluster is embedded in a macrocyclic TREN 4 (TREN = tris(2-aminoethyl)amine) ligand that provides a rigid coordination environment, leading to lower reorganization energy of electron transfer. The empty TREN motif on top of the tricopper cluster may serve as a pendant proton relay (Figure 2B), mimicking the function of carboxylate groups adjacent to the TNC.…”

“…The synergistic delivery of electron and proton at the tricopper cluster serves as a prototype for multiple proton-coupled electron transfer at multimetallic active sites. 22 The tricopper μ 3 -OH species have been isolated and characterized in I,I,I/II,I,I/II,II,I oxidation states. 22 To prepare a synthetic model for NI (Cu II Cu II Cu II (μ 3 -O)), we attempted to further oxidize the tricopper cluster to the II,II,II state using two equivalents of oxidant.…”

“…22 The tricopper μ 3 -OH species have been isolated and characterized in I,I,I/II,I,I/II,II,I oxidation states. 22 To prepare a synthetic model for NI (Cu II Cu II Cu II (μ 3 -O)), we attempted to further oxidize the tricopper cluster to the II,II,II state using two equivalents of oxidant. Treatment of Cu II Cu I Cu I (μ 3 -OH)L with two equivalents of tris(4-bromophenyl)ammoniumyl hexafluorophosphate (0.67 V vs Fc/Fc + in MeCN, Figure 3A) in MeCN resulted in instantaneous bleaching of the dark blue color of ammoniumyl to a yellow solution.…”

“…[ of 2.59 Å, which removes the C 3 symmetry typically observed in TREN 4 tricopper μ-OH and μ-O clusters (Figure 4C). 22 The low-symmetry X-ray diffraction (XRD) structure of Cu I Cu I Cu I (μ 2 -OH 2 )L is reflected by the well-resolved methylene (CH 2 ) 1 H NMR resonances (Figure S3). Nonetheless, the single 1 H NMR peak of μ-OH 2 indicates rapid exchange of the two protons residing on the μ 2 -OH 2 ligand (Figure 4C).…”

“…During the reverse scan, the three one-electron oxidations were observed at −0.95 V (III), −0.47 V (IV), and −0.06 V (IV) vs Fc/Fc + (Figure 5B, black), which matches those observed from the cyclic voltammogram of Cu II Cu I Cu I (μ 3 -OH)L (Figure 5B, red). 22 Anodic waves III, IV, and V are assigned to the consecutive oxidation of Cu I Cu I Cu I (μ 3 -OH)L to Cu II Cu I Cu I (μ 3 -OH)L, Cu II Cu II Cu I (μ 3 -OH)L, and eventually Cu II Cu II Cu II (μ 3 -OH)L, respectively. The last oxidation from Cu II Cu II Cu I (μ 3 -OH)L to Cu II Cu II Cu II (μ 3 -OH)L (Figure 5B, V) is irreversible, suggesting the electron transfer is coupled with an IPT to afford Cu II Cu II Cu II (μ 3 -O)LH (Figure 5C).…”