Cocatalysts copper compounds

Usually the stable nitroxyl radicals alone cannot directly catalyze the oxidation of alcohols with dioxygen or peroxide, so they rely on the assistance of various cocatalysts that play an important role in activating the oxidation agent. The most used cocatalysts are first row transition-metal complexes where Cu compounds with various N-donor ligands account for the prime ones. In many instances this combination serves as some kind of model to compare catalytic properties of copper compounds. For example, the performances of two asymmetric tetranuclear (with the Cu4(p—0)2(p — 0)2 404 core) and dinuclear (with the Cu2(p-0)2N202 core) copper(II) complexes were compared in the catalytic TEMPO-mediated aerobic oxidation ofbenzylic alcohols. In spite of their similarity, the complexes perform differently the tetranuclear copper(II) (R) complex is highly active leading to yields up to 99% and TONs up to 770, while the (S,R)-2 dinuclear complex is not so efficient under the same conditions. However, no solid explanation of the activity differences was proposed. 

Chromium compounds as catalysts, 188 Chromium oxide in catalytic converter, 62 Chromium oxide catalysts, 175-184 formation of active component, 176,177 of Cr-C bonds, 177, 178 propagation centers formation of, 175-178 number of, 197, 198 change in, 183, 184 reduction of active component, 177 Clear Air Act of 1970, 59, 62 Cobalt oxide in catalytic converter, 62 Cocatalysts, 138-141, 152-154 Competitive reactions, 37-43 Copper chromite, oxidation of CO over, 86-88... 

Good yields of carbonyl compounds have also been obtained from the vapor-phase oxidation of alkenes by steam and air over palladium catalysts supported on charcoal.413 In this case, no copper cocatalyst is needed, presumably because palladium(II) is not reduced to palladium(O), but remains in the form of a stabilized palladium(Il) hydride which can react with 02 to give the hydroperoxidic species. 

The synthesis of 1-amino-isoquinoline-A-oxides from 2-alkynylbenzaldoxime and related compounds has been achieved using a silver/copper-cocatalyzed reaction in air (Scheme 3.58) [64]. While silver triflate was used as the silver source, a range of copper salts were screened for activity, and copper iodide was found to be an effective cocatalyst... 

In attempts to recover the chiral Ugand 21, the analogous oxidized phosphoric amide was also isolated. This compound is formed by a copper-catalyzed side-reaction with sulfinate as oxidant and actually works as a cocatalyst that significantly increases the enantioselectivity of the AIMe3 additirai. A similar effect was achieved applying a combination of 21 and hexamethylphosphoric triamide (HMPA), and thus, the improved stereoselectivity was suggested to arise from strong coordination effects. 

Many cocatalysts are responsible only for electron and proton transfer between the metal catalyst and O2, but examples of cocatalyst interaction with the substrate also exist In the example below, Marko and coworkers have shown that the catalytic use of copper in an aerobic alcohol oxidation is achieved through the catalytic addition of an azo compound [19]. The mechanistic studies support the pathways presented in Scheme 5.4 with a Cu(l)-azo oxidant, 8, in which the azo compound abstracts the hydride from the alcohol, 9. 

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