Structural and Functional Models for the Dicopper Site in Hemocyanin. Dioxygen Binding by Copper Complexes of Tris(1-R-4-Rʺ-Imidazolyl-κN)phosphines

Will E. Lynch, Donald M. Kurtz, Shengke Wang, Robert A. Scott

Research output: Contribution to journalArticlepeer-review

86 Scopus citations

Abstract

Complexes of the type [CuI(T1Et4RIP)]X (T1Et4RIP = tris(1-ethyl-4-R-imidazolyl)phosphine (R = methyl (Me), isopropyl (iPr)); X = PF6, ClO4, CF3SO3), in which T1Et4RIP functions as a tridentate nitrogen donor ligand, were prepared by Lewis acid-base reactions between [CuI(CH3CN)(4)]X and T1Et4RIP in dry, degassed solvents. The colorless acetonitrile adducts, [CuI(T1Et4RIP)(CH3CN)]X, were obtained by crystallization from acetontrile. The complex with R = iPr and X = PF6 crystallizes in the space group I213 with a = b = c 18.912(2) Å and Z = 8. The refinement converged with a final R (Rw) value of 0.075 (0.098) for 988 reflections with F > 3σ(Fo). The CUI is coordinated in a trigonally distorted tetrahedral fashion to three imidazolyl nitrogen atoms at 2.08 Å and one acetonitrile nitrogen atom at 1.90 Å. Exposure of dry solutions of these CuI complexes to O2 below -60 ° C resulted in an isolable purple species with spectroscopic and magnetic properties characteristic of (μ-η2·η2-peroxo)dicopper(II) complexes. The representative complex analyzing for ([Cu(T1Et4MeIP)]2(O2))(PF6)2 has the following approximate values : diamagnetic; UV-vis, 3 38 nm (ϵ = 19 000 M-1 cm-1), 521 nm (ϵ = 1000 M-1 cm-1); υ-(O-O), 740 cm-1. The Cu X-ray absorption fine structure spectrum of this complex with X = ClO4 was best fit with a Cu scatterer at 3.48 Å, two O (or N) scatterers at 1.94 Å, and two sets of N (or O) scatterers : two at 2.05 Å and one at 2.30 Å. These spectroscopic, magnetic, and structural properties are characteristic of (μ-η2 2-peroxo)dicopper(II) complexes having a planar Cu2O2 core and terminal nitrogen donor ligands, including the dicopper site in oxyhemocyanin. The [CuI(T1Et4RIP)(CH3CN)]X complexes with R = iPr react with O2 at -78 ° C to produce dioxygen adducts with spectroscopic and magnetic properties very similar to those listed above for R = Me. The complexes with R = iPr, upon repeated thermal cycling between -78 and approximate to-20 ° C in methanol, exhibit reversible binding of dioxygen. This process can be readily monitored by the characteristic visible absorption spectrum of the dioxygen adduct. Thus, copper complexes of tris(imidazolyl)phosphines with 1, 4-disubstituted imidazolyl groups have been successfully used to model spectroscopic, magnetic, structural, and functional properties of the dicopper site in hemocyanin.

Original languageEnglish
Pages (from-to)11030-11038
Number of pages9
JournalJournal of the American Chemical Society
Volume116
Issue number24
DOIs
StatePublished - Nov 1 1994

Scopus Subject Areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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