A trinuclear intermediate in the copper-mediated reduction of O2: four electrons from three coppers.

The reaction of metal complexes with dioxygen (O2) generally proceeds in 1:1, 21, or 41 (metal:O2) stoichiometry. A discrete, structurally characterized 31 product is presented. This mixed-valence trinuclear copper cluster, which contains copper in the highly oxidized trivalent oxidation state, exhibits O2 bond scission and intriguing structural, spectroscopic, and redox properties. The relevance of this synthetic complex to the reduction of O2 at the trinuclear active sites of multicopper oxidases is discussed.

Catalytic galactose oxidase models: biomimetic Cu(II)-phenoxyl-radical reactivity.

Biomimetic functional models of the mononuclear copper enzyme galactose oxidase are presented that catalytically oxidize benzylic and allylic alcohols to aldehydes with O2 under mild conditions. The mechanistic fidelity between the models and the natural system is pronounced. Modest structural mimicry proves sufficient to transfer an unusual ligand-based radical mechanism, previously unprecedented outside the protein matrix, to a simple chemical system.

Biomimetic modeling of copper oxidase reactivity.

Bioinspired copper-model-complexes that react with O(2) provide an opportunity to probe biological reactivity at a small-molecule level of detail. Biological structural information combined with appropriate ligand design has proven sufficient to create Cu:O(2) complexes capable of external substrate oxidation. Most notable developments during the review period are the bioinspired catalysts capable of aerobic alcohol-oxidation. The extension of this oxidative reactivity to other important organic transformations beyond the scope of the inspiring system completes a modeling paradigm.

Synthesis and Characterization of a Family of Systematically Varied Tris(2-pyridyl)methoxymethane Ligands: Copper(I) and Copper(II) Complexes.

An efficient modular protocol for synthesizing a series of facial-capping tris-pyridyl ligands, based on the tris(2-pyridyl)methoxymethane backbone, has been developed which allows for systematic variations of the steric demands at the periphery of the ligand. The coordination chemistry of one such family of ligands that positions 0-->3 methoxy groups at the periphery with Cu(I) and Cu(II) is presented. The ligands are tris(2-pyridyl)methoxymethane (L(0)()), bis(2-pyridyl)(2-(6-methoxy)pyridyl)methoxymethane (L(1)()), bis(2-(6-methoxy)pyridyl)(2-pyridyl)methoxymethane (L(2)()), and tris(2-(6-methoxy)pyridyl)methoxymethane (L(3)()). The ligand exchange behavior and, to a lesser extent, the structures of the these complexes vary dramatically given the small perturbation of introducing methoxy substituents. Two distinct coordination modes are observed for the Cu(I) complexes, both in solution and the solid state. One is a pseudo-tetrahedral coordination comprised of the facial-capping, tris-pyridyl ligand and a monodentate ligand such as CH(3)CN, CO, or PPh(3). The other structural type is also a pseudo-tetrahedral Cu(I) monomer formed by two tris-pyridyl ligands coordinated in a bidentate manner with preferable binding by the nonmethoxy pyridyl subunits. With the exception of the most sterically hindered ligand, L(3)(), which only displays monoligation to Cu(I), all ligands form both types of Cu(I) complexes, and the formation is controlled by stoichiometry. Both competitive ligand binding experiments and ligand substitution with CO(g) show that the [(L(0)())(2)Cu](+) and [(L(1)())(2)Cu](+) complexes have nearly equivalent stability in aprotic solvent, and greater stability than the [(L(2)())(2)Cu](+) complex due to inclusion of bulky methoxypyridines into the Cu(I) coordination sphere. The Cu(II) complexes of the ligand series generate "bis-tris", [(L(0)()(-->)(3)())(2)Cu](2+), complexes, with the Cu(II) ligated in a tetragonally distorted octahedral coordination environment. The degree of bulk at the ligand periphery dictates the Cu(II)-ligand bond lengths both in solution and the solid state. In these complexes, the bulky pyridyl ring prefers to bind in the axial position. For the most sterically encumbered ligand, L(3)(), the bisligated Cu(II) complex is moisture sensitive, reacting to give a monoligated, tris-aqua species, [L(3)()Cu(H(2)O)(3)](2+).

Structural dynamics of a catalytic monolayer probed by ultrafast 2D IR vibrational echoes.

Ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy has proven broadly useful for studying molecular dynamics in solutions. Here, we extend the technique to probing the interfacial dynamics and structure of a silica surface-tethered transition metal carbonyl complex--tricarbonyl (1,10-phenanthroline)rhenium chloride--of interest as a photoreduction catalyst. We interpret the data using a theoretical framework devised to separate the roles of structural evolution and excitation transfer in inducing spectral diffusion. The structural dynamics, as reported on by a carbonyl stretch vibration of the surface-bound complex, have a characteristic time of ~150 picoseconds in the absence of solvent, decrease in duration by a factor of three upon addition of chloroform, and decrease another order of magnitude for the bulk solution. Conversely, solvent-complex interactions increase the lifetime of the probed vibration by 160% when solvent is applied to the monolayer.

Efficient epoxidation of electron-deficient olefins with a cationic manganese complex.

The complex [MnII(R,R-mcp)(CF3SO3)2] is an efficient and practical catalyst for the epoxidation of electron-deficient olefins. This catalyst is capable of epoxidizing olefins with as little as 0.1 mol % catalyst in under 5 min using 1.2 equiv of peracetic acid as the terminal oxidant. A wide scope of substrates are epoxidized including terminal, tertiary, cis and trans internal, enones, and methacrylates with >85% isolated yields.

A stabilized mu-eta(2):eta(2) peroxodicopper(II) complex with a secondary diamine ligand and its tyrosinase-like reactivity.

The activation of dioxygen (O(2)) by Cu(I) complexes is an ubiquitous process in biology and industrial applications. In tyrosinase, a binuclear copper enzyme, a mu-eta(2):eta(2)-peroxodicopper(II) species is generally accepted to be the active oxidant. Reported here is the characterization and reactivity of a stable mu-eta(2):eta(2)-peroxodicopper(II) complex at -80 degrees C using a secondary diamine ligand, N,N'-di-tert-butyl-ethylenediamine (DBED). The spectroscopic characteristics of this complex (UV-vis, resonance Raman) prove to be strongly dependent on the counteranion employed and not on the solvent, suggesting an intimate interaction of the counteranions with the Cu-O(2) cores. This interaction is also supported by solution EXAFS data. This new complex exhibits hydroxylation reactivity by converting phenolates to catechols, proving to be a functional model of tyrosinase. Additional interest in this Cu/O(2) species results from the use of Cu(I)-DBED as a polymerization catalyst of phenols to polyphenylene oxide (PPO) with O(2) as the terminal oxidant.