The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-electron processes. As a result, both radical pathways and powerful two-electron bond forming pathways via organmetallic intermediates, similar to those of palladium, can occur. In addition, the different oxidation states of copper associate well with a large number of different functional groups via Lewis acid interactions or π-coordination. In total, these feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates.

Oxygen is a highly atom economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways.1 The high activation energies in the reactions of oxygen require that catalysts be employed.2 In combination with molecular oxygen, the chemistry of copper catalysis increases exponentially since oxygen can act as either a sink for electrons (oxidase activity) and/or as a source of oxygen atoms that are incorporated into the product (oxygenase activity). The oxidation of copper with oxygen is a facile process allowing catalytic turnover in net oxidative processes and ready access to the higher CuIII oxidation state, which enables a range of powerful transformations including two-electron reductive elimination to CuI. Molecular oxygen is also not hampered by toxic byproducts, being either reduced to water, occasionally via H2O2 (oxidase activity) or incorporated into the target structure with high atom economy (oxygenase activity). Such oxidations using oxygen or air (21% oxygen) have been employed safely in numerous commodity chemical continuous and batch processes.3

However, batch reactors employing volatile hydrocarbon solvents require that oxygen concentrations be kept low in the head space (typically <5–11%) to avoid flammable mixtures, which can limit the oxygen concentration in the reaction mixture.4,5,6 A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability.5 Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed.6 New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space.4a,7 Supercritical carbon dioxide has been found to be advantageous as a solvent due its chemical inertness towards oxidizing agents and its complete miscibility with oxygen or air over a wide range of temperatures.8 An number of flow technologies9 including flow reactors,10 capillary flow reactors,11 microchannel/microstructure structure reactors,12 and membrane reactors13 limit the amount of or afford separation of hydrocarbon/oxygen vapor phase thereby reducing the potential for explosions.

Enzymatic oxidizing systems based upon copper that exploit the many advantages and unique aspects of copper as a catalyst and oxygen as an oxidant as described in the preceding paragraphs are well known. They represent a powerful set of catalysts able to direct beautiful redox chemistry in a highly site-selective and stereoselective manner on simple as well as highly functionalized molecules. This ability has inspired organic chemists to discover small molecule catalysts that can emulate such processes. In addition, copper has been recognized as a powerful catalyst in several industrial processes (e.g. phenol polymerization, Glaser-Hay alkyne coupling) stimulating the study of the fundamental reaction steps and the organometallic copper intermediates. These studies have inspiried the development of nonenzymatic copper catalysts. For these reasons, the study of copper catalysis using molecular oxygen has undergone explosive growth, from 30 citations per year in the 1980s to over 300 citations per year in the 2000s.

A number of elegant reviews on the subject of catalytic copper oxidation chemistry have appeared. Most recently, reviews provide selected coverage of copper catalysts14 or a discussion of their use in the aerobic functionalization of C–H bonds.15 Other recent reviews cover copper and other metal catalysts with a range of oxidants, including oxygen, but several reaction types are not covered.16 Several other works provide a valuable overview of earlier efforts in the field.17 This review comprehensively covers copper catalyzed oxidation chemistry using oxygen as the oxidant up through 2011. Stoichiometric reactions with copper are discussed, as necessary, to put the development of the catalytic processes in context. Mixed metal systems utilizing copper, such as palladium catalyzed Wacker processes, are not included here. Decomposition reactions involving copper/oxygen and model systems of copper enzymes are not discussed exhaustively. To facilitate analysis of the reactions under discussion, the current mechanistic hypothesis is provided for each reaction. As our understanding of the basic chemical steps involving copper improve, it is expected that many of these mechanisms will evolve accordingly.

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Aerobic Copper-Catalyzed Organic Reactions

Organic Solar Cells

Novel multifunctional polymers from aromatic diamines by oxidative polymerizations.

Oxidative polymerization of phenols revisited

Co-ordination polymers

Polymer modified electrodes form a new field that combines polymer chemistry with electrochemistry and which aims at developing new materials for electrocatalysis, electronics, photoelectrochemistry and photoelectronics. This review describes the methods used to prepare polymer coatings on a carrier electrode and discusses various ways of controlling electron processes. The subjects treated include electron transport through the polymer layer, catalysis at the interface, charge storage for polymer batteries, display devices and polymer-based electronics. A central topic is electron pumping in the polymer layer by photophysical and photochemical processes activated by visible light. Several prospective applications are mentioned.

Polymer-coated electrodes: New materials for science and industry

It was found that the oxidative polymerization of 2.6-xylenol with a copper-amine complex proceeds via a mechanism similar to that of a MICHAELIS-MENTEN-type reaction, the steady state being maintained during the polymerization; the kinetics were studied. The LINEWEAVER-BURK plots showed linear relationships, supporting this mechanism. From the comparison of the kinetic constants it was concluded that oxygen not only takes part in the recycling step of the catalyst, but also promotes the catalytic action of the cuprous complex by being coordinated to the intermediate complex. K1 values (the reciprocal of the MICHAELIS constant, Km) vary with the amine-ligand species, but the reaction-rate constants (k2) do not change, regardless of the ligands used. According to the kinetic formula, K1 is proportional to the product of the formation constant of the complex between the copper-amine catalyst and the monomer (K′1) by the rate constant of electron transfer (ke). It is because of the K′1 values that the apparent polymerization rate varies with the amine ligands in the region of relatively low monomer concentrations. It was found that, as the ligand ratio ([pyridine]/[Cu]) increases, i.e., as the selectivity for CO coupling increases, the K1 values become larger. The mechanism for the coupling selectivity is discussed in relation to the K1 values.



Es wurde gefunden, das die oxidative Polymerisation des 2.6-Dimethylphenols mit Kupfer(II)-Amin-Komplexen dem Mechanismus der MICHAELIS-MENTEN-Reaktion folgt, wobei der stationare Zustand erhalten bleibt. Die Kinetik der Polymerisation wurde untersucht. Die LINEWEAVER-BURK-Darstellung der Polymerisationsgeschwindigkeit bestatigt den gefundenen Mechanismus. Aus dem Vergleich der kinetischen Konstanten wurde geschlossen, das der Sauerstoff nicht nur die Regenerierung des Katalysators bewirkt, sondern auch die Elektronenubertragungsreaktion oder die Dissoziationsreaktion der aktivierenden Monomeren fordert. K1 (= 1/Km;Km : MICHAELIS-Konstante) ist abhangig von den Aminliganden, die Polymerisationsgeschwindigkeitskonstante k2 jedoch ist nahezu konstant. K1 ist proportional dem Produkt aus K′1 (Komplexbildungskonstante zwischen Kupfer-Amin-Komplex und Monomerem) und ke (Geschwindigkeitskonstante der Elektronenubertragung). Es ist auf die K1-Werte zuruckzufuhren, das die scheinbare Polymerisationsgeschwindigkeit im Gebiet niedriger Monomerkonzentration vom Aminliganden abhangig ist. Es wurde gefunden, das K1 mit zunehmender Selektivitat fur die CO-Kuppelung anwachst. Der Mechanismus der Kuppelung wurde in bezug auf K1 diskutiert.

The kinetics of the oxidative polymerization of 2.6-xylenol with a copper-amine complex

In order to study the catalytic effects of the polymer-ligand, copper-poly(vinylpyridine) (Cu-PVP) complexes were used as catalyst for the oxidative polymerization of phenols. The catalysis was discussed.



The rate of the 2,6-dimethylphenol (XOH) polymerization catalyzed by the Cu-PVP complex was slower than that catalyzed by a Cu-pyridine complex. By the measurement of the kinetic constants, it was suggested that a bulky PVP ligand obstructed the coordination-step of the monomer and the electron-transfer-step from the coordinated monomer to the cupric ion. The polymerization of the mixture of XOH and o-cresol with Cu-PVP as catalyst was saturated at a higher conversion, and the yield and the molecular weight of the polymer obtained were larger than in the cases where the Cu-pyridine or the Cu-γ-picoline complex systems were used as catalysts. XOH is preferentially activated by the Cu-PVP catalyst because its oxidation potential is lower, thus the effect of the PVP ligand may be observed.



XOH was polymerized by the swelled Cu-PVP complex as a heterogeneous catalyst in benzene or a benzene containing mixture of solvents. The catalyst was recovered by filtration in a high yield and re-used repeatedly. Cu-PVP complexes are relatively stable toward alkali because of their chelate structure. The polymerization was accelerated 3 to 5 times in alkaline solution, and the side-reaction was suppressed.



Um die katalytische Wirkung des Polymer-Liganden zu untersuchen, wurden Kupfer-Poly(vinylpyridin) (Cu-PVP)-Komplexe als Katalysatoren fur die oxydative Polymerisation der Phenole eingesetzt. Der Katalyseverlauf wurde diskutiert.



Die mit dem Cu-PVP-Komplex katalysierte Polymerisation des 2,6-Dimethylphenols verlief langsamer als die mit dem Kupfer-Pyridin-Komplex katalysierte. Aufgrund der Messung der kinetischen Konstanten wurde angenommen, das der raumfullende PVP-Ligand die Koordination des Monomeren zum Metall stort. Die Polymerisation des Monomerengemisches aus XOH und o-Kresol verlief in Gegenwart des Cu-PVP-Katalysators bei hoheren Umsatzen mit konstanter Geschwindigkeit. Die Ausbeute und das Molekulargewicht des erhaltenen Polymeren waren groser als in den Fallen, in denen Cu-Pyridinoder Cu-γ-Pikolin-Komplexe als Katalysatorsysteme verwandt wurden. XOH wird vorzugsweise mit dem Cu-PVP-Katalysator aktiviert, da das Oxydationspotential des XOH niedriger ist; dadurch wird die Wirkung des PVP-Liganden erfasbar.

The catalytic effects of the poly(vinylpyridine)‐ligand in the oxidative polymerization of phenols

3 Photoindueed Charge Separation and Electron Relay in Molecular and Polymer Assemblies . . . . . . . . . . . . . . . . . . . . . . . 7 3.1 Conversion Systems on Molecular Assemblies . . . . . . . . . . . . 8 3.2 Polymer Systems in Solution . . . . . . . . . . . . . . . . . . . 14 3.3 Polymer Systems as Solid Phase . . . . . . . . . . . . . . . . . . 22 3.4 Polymer Supported Meta l Colloids as Catalyst . . . . . . . . . . . 26

Solar energy conversion by functional polymers

Water-soluble cobalt(III) chelates having a polymeric ligand such as cis-[Co(en)2-PVPCl]Cl2 and cis-[Co-(trien)PVPCl]Cl2 (PVP = poly-4-vinylpyridine) were prepared by substitution reactions between cobalt(III) chelate and PVP in water–alcohol solution. PVP of different degrees of polymerization was used as the ligand in preparation of these complexes. The PVP complexes were identified and their properties ascertained by microanalysis and by a study of the infrared, ultraviolet, visible, and PMR spectra. Most of the characteristic properties of these complexes may be ascribed to the polymeric structure of the PVP ligand.

Masao Kaneko

Papers

Polymer-coated electrodes: New materials for science and industry

The kinetics of the oxidative polymerization of 2.6-xylenol with a copper-amine complex

The catalytic effects of the poly(vinylpyridine)‐ligand in the oxidative polymerization of phenols

Solar energy conversion by functional polymers

Preparation and properties of some water‐soluble cobalt (III)–poly‐4‐vinylpyridine complexes