Synthesis of a tetracopper assembly complex comprised of one macrocyclic dinuclear copper unit and two mononuclear copper units: Intramolecular electron transfer relevant to multicopper oxidase

Yuko Suetsugu, Yuko Mitsuka, Yuji Miyasato, Masaaki Ohba, Hisashi Okawa

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Abstract

The dinuclear copper(II) complex [Cu 2(L 1)](ClO 4) 2·CH 3OH·2H 2O (1) of a macrocyclic ligand H 2L 1, derived from the cyclic [2:2] condensation of 2,6-diformyl-4-methylphenol and 1,1,1-tri(aminomethyl)ethane, has been prepared as the type 3 copper site for modeling multicopper oxidase: 1 has two auxiliary amino groups on the macrocyclic framework. The condensation of 1 with two molecules of 2-formylpyridine through the amino groups afforded [Cu 2(L 2)](ClO 4) 2·2DMF (2). This has a Cu⋯Cu separation of 4.434(1) Å with no direct bridge between the two copper atoms, owing to the involvement of the auxiliary 2-pyridylmethylimino residue in coordination. The condensation of 1 with two molecules of 3-[N,N-di(2-pyridylmethyl)aminomethyl]-5-methylsalicylaldehyde in the presence of Cu(ClO 4) 2·6H 2O afforded the tetracopper assembly complex [Cu 4(L 3)](ClO 4) 4·3H 2O (3), which is comprised of a macrocyclic dinuclear Cu 2(II,II) unit and two mononuclear Cu(II) units, {Cu(II)-Cu 2(II,II)-Cu(II)}. Cyclic voltammograms of 3 exhibit a two-electron redox process at -0.77 V (vs Ag/Ag +) followed by two one-electron redox processes at -0.85 and -1.29 V. Coulometric studies combined with spectroscopic and EPR studies demonstrate that the redox process at -0.77 V involves the reduction of two mononuclear Cu(II) units followed by an intramolecular electron transfer from one of the reduced Cu(I) units to the dinuclear Cu 2(II,II) unit: {Cu(II)-Cu 2(II,II)-Cu(II)}/ {Cu(I)-Cu 2(II,II)-Cu(I)} → {Cu(I)-Cu 2(I,II)-Cu(II)}. The resulting {Cu(I)-Cu 2(I,II)-Cu(II)} species is further reduced to {Cu(I)-Cu 2(I,II)-Cu(I)} at -0.85 V and to {Cu(I)-Cu 2(I,I)-Cu(I)} at -1.29 V.

Original languageEnglish
Pages (from-to)595-601
Number of pages7
JournalBulletin of the Chemical Society of Japan
Volume79
Issue number4
DOIs
Publication statusPublished - Nov 9 2006

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All Science Journal Classification (ASJC) codes

  • Chemistry(all)

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