title: Tridentate copper ligand influences on heme-peroxo-copper formation and properties: reduced, superoxo, and mu-peroxo iron/copper complexes.
abstract: In cytochrome c oxidase synthetic modeling studies, we recently reported a new mu-eta2:eta2-peroxo binding mode in the heteronuclear heme/copper complex [(2L)Fe(III)-(O2(2-))-CuII]+ (6) which is effected by tridentate copper chelation (J. Am. Chem. Soc. 2004, 126, 12716). To establish fundamental coordination and O2-reactivity chemistry, we have studied and describe here (i) the structure and dioxygen reactivity of the copper-free compound (2L)FeII (1), (ii) detailed spectroscopic properties of 6 in comparisons with those of known mu-eta2:eta1 heme-peroxo-copper complexes, (iii) formation of 6 from the reactions of [(2L)FeIICuI]+ (3) and dioxygen by stopped-flow kinetics, and (iv) reactivities of 6 with CO and PPh3. In the absence of copper, 1 serves as a myoglobin model compound possessing a pyridine-bound five-coordinate iron(II)-porphyrinate which undergoes reversible dioxygen binding. Oxygenation of 3 below -60 degrees C generates the heme-peroxo-copper complex 6 with strong antiferromagnetic coupling between high-spin iron(III) and copper(II) to yield an S = 2 spin system. Stopped-flow kinetics in CH2Cl2/6% EtCN show that dioxygen reacts with iron(II) first to form a heme-superoxide moiety, [(EtCN)(2L)FeIII-(O2-)...CuI(EtCN)]+ (5), which further reacts with Cu(I) to generate 6. Compared to those properties of a known mu-eta2:eta1-heme-peroxo-copper complex, 6 has a significantly diminished resonance Raman nu(O-O) stretching frequency at 747 cm(-1) and distinctive visible absorptions at 485, 541, and 572 nm, all of which seem to be characteristics of a mu-eta2:eta2-heme-peroxo-copper system. Addition of CO or PPh3 to 6 yields a bis-CO adduct of 3 or a PPh(3) adduct of 5, the latter with a remaining FeIII-(O2-) moiety.
authors.affiliation: Department of Chemistry, Remsen Hall, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Eunsuk
authors.initials: E
authors.lastname: Kim
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Helton
authors.forename: Shen
authors.initials: S
authors.lastname: Lu
authors.forename: Pierre
authors.initials: P
authors.lastname: Moënne-Loccoz
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Incarvito
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: Susan
authors.initials: S
authors.lastname: Kaderli
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Zuberbühler
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Karlin
mesh_terms: D003300:Copper / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010545:Peroxides / Q000737:chemistry*
chemical_list: D008024:Ligands; D010545:Peroxides; D006418:Heme; D003300:Copper; D007501:Iron