Observation of a Cu(II)(2) (μ-1,2-peroxo)/Cu(III)(2) (μ-oxo)(2) equilibrium and its implications for copper-dioxygen reactivity.

Synthesis of small-molecule Cu2 O2 adducts has provided insight into the related biological systems and their reactivity patterns including the interconversion of the Cu(II) 2 (μ-η(2) :η(2) -peroxo) and Cu(III) 2 (μ-oxo)2 isomers. In this study, absorption spectroscopy, kinetics, and resonance Raman data show that the oxygenated product of [(BQPA)Cu(I) ](+) initially yields an "end-on peroxo" species, that subsequently converts to the thermodynamically more stable "bis-μ-oxo" isomer (Keq =3.2 at -90 °C).

Reversible dioxygen binding and arene hydroxylation reactions: Kinetic and thermodynamic studies involving ligand electronic and structural variations.

Copper-dioxygen interactions are of intrinsic importance in a wide range of biological and industrial processes. Here, we present detailed kinetic/thermodynamic studies on the O(2)-binding and arene hydroxylation reactions of a series of xylyl-bridged binuclear copper(I) complexes, where the effects of ligand electronic and structural elements on these reactions are investigated. Ligand 4-pyridyl substituents influence the reversible formation of side-on bound μ-η(2):η(2)-peroxodicopper(II) complexes, with stronger donors leading to more rapid formation and greater thermodynamic stability of product complexes [Cu(II) (2)((R)XYL)(O(2) (2-))](2+).

Further insights into the spectroscopic properties, electronic structure, and kinetics of formation of the heme-peroxo-copper complex [(F8TPP)FeIII-(O2(2-)-CuII(TMPA)]+.

In the further development and understanding of heme-copper O2-reduction chemistry inspired by the active-site chemistry in cytochrome c oxidase, we describe a dioxygen adduct, [(F8TPP)FeIII-(O22-)-CuII(TMPA)](ClO4) (3), formed by addition of O2 to a 1:1 mixture of the porphyrinate-iron(II) complex (F8TPP)FeII (1a) {F8TPP = tetrakis(2,6-difluorophenyl)porphyrinate dianion} and the copper(I) complex [(TMPA)CuI(MeCN)](ClO4) (1b) {TMPA = tris(2-pyridylmethyl)amine}. Complex 3 forms in preference to heme-only or copper-only binuclear products, is remarkably stable {t1/2 (RT; MeCN) approximately 20 min; lambda max = 412 (Soret), 558 nm; EPR silent}, and is formulated as a peroxo complex on the basis of manometry {1a/1b/O2 = 1:1:1}, MALDI-TOF mass spectrometry {16O2, m/z 1239 [(3 + MeCN)+]; 18O2, m/z 1243}, and resonance Raman spectroscopy {nu(O-O) = 808 cm-1; Delta16O2/18O2 = 46 cm-1; Delta16O2/16/18O2 = 23 cm-1}. Consistent with a mu-eta2:eta1 bridging peroxide ligand, two metal-O stretching frequencies are observed {nu(Fe-O) = 533 cm-1, nu(Fe-O-Cu) = 511 cm-1}, and supporting normal coordinate analysis is presented.

Tridentate copper ligand influences on heme-peroxo-copper formation and properties: reduced, superoxo, and mu-peroxo iron/copper complexes.

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.

Dioxygen reactivity of copper and heme-copper complexes possessing an imidazole-phenol cross-link.

Recent spectroscopic, kinetics, and structural studies on cytochrome c oxidases (CcOs) suggest that the histidine-tyrosine cross-link at the heme a3-CuB binuclear active site plays a key role in the reductive O2-cleavage process. In this report, we describe dioxygen reactivity of copper and heme/Cu assemblies in which the imidazole-phenol moieties are employed as a part of copper ligand LN4OH (2-{4-[2-(bis-pyridin-2-ylmethyl-amino)-ethyl]-imidazol-1-yl}-4,6-di -tert-butyl-phenol). Stopped-flow kinetic studies reveal that low-temperature oxygenation of [CuI(LN4OH)]+ (1) leads to rapid formation of a copper-superoxo species [CuII(LN4OH)(O2-)]+ (1a), which further reacts with 1 to form the 2:1 Cu:O2 adduct, peroxo complex [{CuII(LN4OH)}2(O2(2-))]2+ (1b).

Heme/Cu/O2 reactivity: change in FeIII-(O2 2-)-CuII unit peroxo binding geometry effected by tridentate copper chelation.

A new heme-peroxo-copper complex structural type with mu-eta2:eta2 peroxo ligation has been generated utilizing a heterobinucleating ligand with bis(2-(2-pyridyl)ethyl)amine tridentate chelate for copper. Oxygenation of [(2L)FeIICuI]+ (1) at -80 degrees C in CH2Cl2/6%EtCN, 1 (lambdamax, 426, 530 nm) produces [(2L)FeIII-(O22-)-CuII)]+ (3) (lambdamax, 419, 488, 544, 575 nm). Stopped-flow kinetic/spectroscopic probing reveals that a superoxo complex, [(2L)FeIII-(O2-).

Solvent effects on the conversion of dicopper(II) micro-eta(2):eta(2)-peroxo to bis-micro-oxo dicopper(III) complexes: direct probing of the solvent interaction.

A new tridentate ligand, PYAN, is employed to investigate solvent influences for dioxygen reactivity with [Cu(PYAN)(MeCN)]B(C(6)F(5))(4) (1). Stopped-flow kinetic studies confirm that the adducts [[u(II)(PYAN)]2)(O(2))][B(C(6)F(5))(4)](2) (2(Peroxo)) and [[u(III)(PYAN)]2)(O)(2)][B(C(6)F(5))(4)](2) (2(Oxo)) are in rapid equilibrium. Thermodynamic parameters for the equilibrium between 2(Peroxo) and 2(Oxo) re as follows: THF, deltaH degrees approximately -15.

Dicopper peroxo complexes: low temperature stopped-flow reaction kinetics of [(BQPA)CuI]+ and [(Me2-TMPA)CuI]+.

In the last 20 years, the reaction of many different CuI complexes and with dioxygen has been described. There is quite a big variety in their coordination geometry and most of them have been characterized by X-ray crystallography. Beyond structural information, stopped-flow kinetics experiments have provided additional mechanistic insights.

Dicopper and heteronuclear iron-copper peroxo complex formation: kinetics and thermodynamics.

Quasireversible adducts of dioxygen with Cu(I) complexes are of interest as models for dioxygen transport proteins, for oxygen-dependent copper redox enzymes, and for low-molecular oxidation and oxygenation catalysts. Depending on ligand denticity and structural factors dioxygen binds in various geometries and metal:O2 ratios to the reduced copper centers. Kinetic investigations produce detailed mechanistic insight into the nature of coppers-dioxygen interaction.

Copper(I) and copper(II) complexes possessing cross-linked imidazole-phenol ligands: structures and dioxygen reactivity.

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.

Copper(I)-phenolate complexes as models of the reduced active site of galactose oxidase: synthesis, characterization, and O2 reactivity.

The Cu(I)-phenolate complexes (1)LCu and (2)LCu and the Cu(I)-phenol complex [H(2)LCu(CNC(6)H(3)Me(2))]BArF(4) were prepared and structurally characterized by X-ray crystallography, where (1)L(-) and (2)L(-) are ligands comprised of a 2,4-di- tert-butylphenolate linked to 1-isopropyl-1,5-diazacyclooctane or 1,4-diisopropyl-1,4,7-triazacyclononane, respectively. The reduced galactose oxidase (GAO) structural models (1)LCu and (2)LCu were found to be highly reactive with O(2), and through combined stopped-flow kinetic and EPR, UV-vis, and resonance Raman spectroscopic studies of the oxygenation of (2)LCu at low temperature, new intermediates relevant to those postulated for the active site oxidation step of the GAO catalytic cycle were identified. The oxygenation was shown by kinetics experiments to proceed via initial binding of O(2) to yield a green, unusually thermodynamically stable 1:1 adduct, (2)LCu(O(2)).

Copper(I)-dioxygen reactivity of [(L)Cu(I)](+) (L = tris(2-pyridylmethyl)amine): kinetic/thermodynamic and spectroscopic studies concerning the formation of Cu-O2 and Cu2-O2 adducts as a function of solvent medium and 4-pyridyl ligand substituent variations.

The kinetic and thermodynamic behavior of O(2)-binding to Cu(I) complexes can provide fundamental understanding of copper(I)/dioxygen chemistry, which is of interest in chemical and biological systems. Here we report stopped-flow kinetic investigations of the oxygenation reactions of a series of tetradentate copper(I) complexes [(L(R))Cu(I)(MeCN)](+) (1(R), R=H, Me, tBu, MeO, Me(2)N) in propionitrile (EtCN), tetrahydrofuran (THF), and acetone. The syntheses of 4-pyridyl substituted tris(2-pyridylmethyl)amine ligands (L(R)) and copper(I) complexes are detailed.

Reversible binding of dioxygen by the copper(I) complex with tris(2-dimethylaminoethyl)amine (Me6tren) ligand.

At low temperatures, the mononuclear copper(I) complex of the tetradentate tripodal aliphatic amine Me(6)tren (Me(6)tren = tris(2-dimethylaminoethyl)amine) [Cu(I)(Me(6)tren)(RCN)](+) first reversibly binds dioxygen to form a 1:1 Cu-O(2) species which further reacts reversibly with a second [Cu(I)(Me(6)tren)(RCN)](+) ion to form the dinuclear 2:1 Cu(2)O(2) adduct. The reaction can be observed using low temperature stopped-flow techniques. The copper superoxo complex as well as the peroxo complex were characterized by resonance Raman spectroscopy.

Tuning copper-dioxygen reactivity and exogenous substrate oxidations via alterations in ligand electronics.

Copper(I)-dioxygen adducts are important in biological and industrial processes. For the first time we explore the relationship between ligand electronics, CuI-O2 adduct formation and exogenous substrate reactivity. The copper(I) complexes [CuI(R-MePY2)]+ (1R, where R = Cl, H, MeO, Me2N) were prepared; where R-MePY2 are 4-pyridyl substituted bis[2-(2-pyridyl)ethyl]methylamine chelates.

Contrasting copper-dioxygen chemistry arising from alike tridentate alkyltriamine copper(I) complexes.

Copper(I)-dioxygen interactions are of great interest due to their role in biological O2-processing as well as their importance in industrial oxidation processes. We describe here the study of systems which lead to new insights concerning the factors which govern Cu(II)-mu-eta2:eta2 (side-on) peroxo versus Cu(III)-bis-mu-oxo species formation. Drastic differences in O2-reactivity of Cu(I) complexes which differ only by a single -CH3 versus -H substituent on the central amine of the tridentate ligands employed are observed.

Intramolecular Ligand Hydroxylation: Mechanistic High-Pressure Studies on the Reaction of a Dinuclear Copper(I) Complex with Dioxygen.

We provide a mechanistic study of a monooxygenase model system and detail low-temperature stopped-flow kinetics studies in acetone as solvent, employing both the use of rapid-scanning diode-array observation and variable high-pressure (20-100 MPa) techniques. The dicopper(I) complex employed is [Cu(2)(H-XYL-H)](2+) (1), with the H-XYL-H ligand wherein a m-xylyl group links two bis[2-(2-pyridyl)ethyl]amine units. This reacts with O(2) reversibly (k(1)/k(-)(1)) giving a peroxo-dicopper(II) intermediate [Cu(2)(H-XYL-H)(O(2))](2+) (2), which thereupon irreversibly (k(2)) reacts by oxygen atom insertion (i.