부산대학교 도서관

In the further development and understanding of heme-copper dioxygen reactivity relevant to cytochrome c oxidase O2-reduction chemistry, we describe a high-spin, five-coordinate dioxygen (peroxo) adduct of an iron(II)-copper(I) complex, [(6L)FeIICuI](BArF20) ( 1), where 6L is a tetraarylporphyrinate with a tethered tris(2-pyridylmethyl)amine chelate for copper. Reaction of 1 with O2 in MeCN affords a remarkably stable [ t1/2 (rt; MeCN)≈60 min] adduct, [(6L)FeIII-(O22-)-CuII]+ ( 2) [EPR silent; λmax=418 (Soret), 561 nm], formulated as a peroxo complex based on manometry ( 1:O2=1:1; spectrophotometric titration, −40 °C, MeCN), mass spectrometry {MALDI-TOF-MS: 16O2, m/ z 1191 ([(6L)FeIII-(16O22−)-CuII]+); 18O2, m/ z 1195}, and resonance Raman spectroscopy (ν(O-O)=788 cm–1; Δ16O2/18O2=44 cm–1; Δ16O2/16/18O2=22 cm–1). 1H and 2H NMR spectroscopy (−40 °C, MeCN) reveals that 2 is the first heme-copper peroxo complex which is high-spin, with downfield-shifted pyrrole resonances (δpyrrole=75 ppm, s, br) and upfield shifted peaks at δ= −22, −35, and −40 ppm, similar to the pattern observed for the μ-oxo complex [(6L)FeIII-O-CuII](BArF) ( 3) (known S=2 system, antiferromagnetically coupled high-spin FeIII and CuII). The corresponding magnetic moment measurement (Evans method, CD3CN, −40 °C) also confirms the S=2 spin state, with μB=4.9. Structural insights were obtained from X-ray absorption spectroscopy, showing Fe–O (1.83 Å) and Cu–O (1.882 Å) bonds, and an Fe...Cu distance of 3.35(2) Å, suggestive of a μ-1,2-peroxo ligand present in 2. The reaction of 2 with cobaltocene gives 3, differing from the observed full reduction seen with other heme-Cu peroxo complexes. Finally, thermal decomposition of 2 yields 3, with concomitant release of 0.5 mol O2 per mol 2, as confirmed quantitatively by an alkaline pyrogallol dioxygen scavenging solution. [ABSTRACT FROM AUTHOR]