title: Copper(I) and copper(II) complexes possessing cross-linked imidazole-phenol ligands: structures and dioxygen reactivity.
abstract: Catalytic reduction of O2 to H2O, and coupling to membrane proton translocation, occurs at the heterobinuclear heme a3-CuB active site of cytochrome c oxidase. One of the CuB ligated histidines is cross-linked to a neighboring tyrosine (C-N bond; tyrosine C6 and histidine epsilon-nitrogen), and the protic residue of this cross-linked His-Tyr moiety is proposed to participate as both an electron and a proton donor in the catalytic dioxygen reduction event. To provide insight into the chemistry of such a moiety, we have synthesized and characterized tetra- and tridentate pyridylalkylamine chelate ligands {LN4OR and LN3OR (R = H or Me)}, which include an imidazole-phenol (or anisole) cross-link and their copper(I/II) complexes. [CuI(LN4OH)]B(C6F5)4 (1) reacts with dioxygen at -80 degrees C in THF, forming an unstable trans-mu-1,2-peroxodicopper(II)complex, which subsequently converts to a dimeric copper(II)-phenolate complex [{Cu(LN4O-)}2](B(C6F5)4)2 (5a). The close analogue [CuI(LN4OMe)]B(C6F5)4 (3) binds dioxygen reversibly at -80 degrees C in tetrahydrofuran. Stopped-flow kinetics of the reaction [CuI(LN3OH)]ClO4 (2) with O2 in CH2Cl2 indicate a steady formation of the purple dimeric product [{Cu(LN3O-)}2](ClO4)2 (5b), which has been analyzed in the temperature range from -40 to +20 degrees C, DeltaH = -9.6 (6) kJ mol-1, DeltaS = -168 (2) J mol-1 K-1 (k(-40 degrees C) = 1.05(4) x 106 and k(+20 degrees C) = 4.6(2) x 105 M-2 s-1). The X-ray crystal structures of 1, [CuII(LN3OH)(MeOH)(OClO3-)](ClO4) (4), 5a, and 5b are reported.
authors.affiliation: Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Kaliappan
authors.initials: K
authors.lastname: Kamaraj
authors.forename: Eunsuk
authors.initials: E
authors.lastname: Kim
authors.forename: Benedikt
authors.initials: B
authors.lastname: Galliker
authors.forename: Lev N
authors.initials: LN
authors.lastname: Zakharov
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
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*; D018360:Crystallography, X-Ray; D003576:Electron Transport Complex IV / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*
chemical_list: D007093:Imidazoles; D010636:Phenols; D003300:Copper; D003576:Electron Transport Complex IV; D010100:Oxygen