Copper complexes amine oxides

Aminated Polystyrene-Copper Complexes as Oxidation Catalysts The Effect of the Degree of Substitution on Catalytic Activity... 

The catalytic activity of copper complexes in oxidative coupling of 2,6-DMP to PPO is significantly improved when polymer-bound 4-aminopyridine is used as ligand [92]. Basic copper-amine complexes also catalyze the oxidative coupling of 2,6-disubstituted phenols [82]. Depending on the size of substituents and the conditions, polymerization or diphenoquinone formation may predominate [83-86]. Small substituents like methyl favor the PPO product. 

Furthermore, the presence of bipyridyl increased the selectivity of the copper catalyzed oxidation to peracetic acid. For example, oxidation of propionaldehyde in acetic acid at 30 °C in the presence of [Cu(bipy)2(N03)2] gave the peracid in 58% yield and the acid in yields of 32-40%. When reaction was run using Cu(N03)2 in the absence of bipyridyl, the peracid was formed in 9% yield while the yield of carboxylic acid was 80%. The nature of the amine was varied and the catalytic activity of the copper complex toward oxidation of propionaldehyde varied with the amine as follows bipyridyl, phenanthroline > none, pyridine > 2,9-dimethyl-l, 10-phenan-throline > quinoline > ethylenediamine. The rate equations for oxidation in the presence of Cu(N03)2 and [Cu(bipy)2(N03)2] differed substantially and the apparent activation energies were 8.2 and lO.lkcal/mole, respectively [241]. 

Two other refining processes are also frequently employed. One involves hydrometallurgical refining in which sulfide concentrates are leached with ammonia solution to convert the copper, nickel, and cobalt sulfides into their complex amines. Copper is precipitated from this solution upon heating. Under such conditions, the sulfide-amine mixture of nickel and cobalt are oxidized to their sulfates. The sulfates then are reduced to metalhc nickel and cobalt by heating with hydrogen at elevated temperatures under pressure. The metals are obtained in their powder form. 

Dimethylphenol is oxidatively polymerized to poly(2,6-dimethyl-1,4-phenyl-ene ether) with a copper-amine complex by a laccaselike reaction. The activated phenols are coupled to form a dimer. The dimer is activated by a mechanism similar to that by which the polymerization proceeds. The effects of the amine ligands are to improve the solubility and the stability of the copper complex as well as the phenol-coordinated complex and to control the redox potential of the copper complex. 

Many amine-copper complexes, as well as a few amine complexes of other metals, and certain metal oxides have since been shown to induce similar reactions (17, 18, 22, 23, 30). This chapter is concerned largely with the mechanism of oxidative polymerization of phenols to linear polyarylene ethers most of the work reported has dealt with the copper-amine catalyzed oxidation of 2,6-xylenol, which is the basis for the commercial production of the polymer marketed under the trade name PPO, but the principal features of the reaction are common to the oxidative polymerization of other 2,6-disubstituted phenols. 

Recently, White (32) observed that under certain conditions ( —15°C., large excess of amine base) oxidation of the dimer derived from 2,6-xylenol with a limited amount of preoxidized copper complex yielded the tetramer as the major product, with small amounts of hexamer and only traces of monomer and trimer. The two rings are indistinguishable in this case, but there is little doubt, in view of the results of Mijs, that... 

Macrocyclic polythioethers form coordination compounds with many transition metal ions [55] and, owing to their moderate rr-acidity (intermediate between that of amines and phosphines), can exert a stabilizing effect on lower oxidation states of the encircled metal [56]. Copper complexes of thiacrowns have been widely investigated, even in view of the fact that they can be considered convenient models in the study of redox properties of cuproproteins (systems whose active site is a copper center bound to the thioether groups of methionine residues [57]). 

Naphthol can successfully be dimerized oxidatively, selectively through the o-site to give (22) using copper(II)-amine complexes (70%) or manganese(III) acetylacetonate (69%), and o-o coupling is the major paAway (90%) on ferricyanide oxidation of the trisubstituted phenol (23) to the orthodiphenoqui-none (24). In this context it is of interest that a compound obtained (74%) on ferricyanide oxidation of... 

Bovine serum amine oxidase (BSAO) is a copper-containing amine oxidase which utilizes a covalently bound 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor in the two-electron oxidation of a broad spectrum of primary amines [99]. The oxidation is thought to proceed via the formation of an iminium complex between the oxidized form of the cofactor and the primary amine (1 in Scheme 10.4). The substrate imine undergoes deprotonation to form product imine, which, after hydrolysis, releases aldehyde product and reduced cofactor [100]. Proton transfer is either partially or largely rate-limiting for the oxidation of benzylamines, as evidenced by a large deuterium isotope effect at the methylene adjacent to the amino group [36, 101, 102]. 

Similar techniques have been tested by various authors297 for a variety of substituted and also for long-chain acetylenes. The reaction is particularly smooth in the presence of a copper(i)-amine complex in an organic solvent pyridine and A A A -tetramethylethylenediamine have been used as the amine.298 Detailed directions for the preparation of 1,4-diphenylbutadiyne by oxidative dimerization of phenylacetylene have been given by Campbell and Eglington.299... 

Oxidative phenoiic coupling. Copper complexes have been used under aerobic conditions to oxidize phenols to quinones and to products of cleavage. Feringa and Wynberg have now found that Cu(lll amine complexes under anaerobic conditions can effect oxidative coupling of phenols. Some typical... 

For Class B (substitution labile) metal complexes, reequilibration to more thermodynamically favorable coordination modes will be very rapid relative to immobilization. Such behavior is typical of first-row TM complexes. In addition, these ions are usually very oxophilic, so the metal complexes are typically subject to ICC interactions with oxide materials. Since these metal ions are generally immobilized under conditions of thermodynamic control, all pertinent speciation equilibria, including ICC reactions (Section III.B), must be considered in order to understand or predict the outcome of immobilization reactions. It is essential to understand the relevant equilibria if direct imprinting of active site structures is to be successful. The studies of Klonkowski et al. (210-213), for example, underscore this point Sol-gel immobilization of copper complexes bearing silylated amine and ethylenediamine ligands were shown by EPR to result in multiple copper environments, suggesting competition between immobilization and ICC reactions. 

An increase in the rate of oxidation of hydroquinone and pyrocatechol by the action of Cu(II), Co(II), Fe(Il), and Mn(II) metal complexes with PEI has been observed [94]. The rate of quinone accumulation depends on the type of metal ion entering the coordination sphere and increases in the following order Cu(II)>Co(II)>Fe(II)>Mn(II). Furthermore, the oxidation of hydroquinone catalyzed by Cu(II) complexes with PVI, PEI and vinyl-amine-vinyl acetate copolymer has been studied in an aqueous solution at 25 °C [95]. In addition, the oxidation of hydroquinone by PVI-Cu(II) and vinylimidazole-vinyl sulfide Vl-VS/Cu(II) complexes has exibited somewhat a typical behavior of copper complexes with copolymers [96]. For example, in respect of VI-VS/Cu(lI) complexes, hydroquinone is oxidized quite rapidly only during the initial phase of the reaction. However, thereafter it changes only slightly. Deviation from linearity has been observed on increasing the content of vinyl sulfide units in the VI-VS copolymer. 

Thus the catalytic activity of amine complexes of copper (II) reaches a maximum after full replacement of Cl -bridged ligands by OH -bridged ones (Fig. 12). However, for copper complexes of polyamidoamines, the maximum of the rate of DMP oxidation has been achieved at a NaOH/Cu ratio of 0.5 instead of 1 as is the case for other polymer ligands [128]. The authors attribute this to the fact that mixed complexes of PAA-Cu(OH)Cl Cu-PAA-type behave as catalyticcdly active species. 

Carbon monoxide co-ordinated to copper(i) amine complexes has been found to be much more susceptible to oxidants than is carbon monoxide in... 

Copper(II)-amine complexes are widely used and very effective phenolic oxidative coupling reagents. Since the reaction proceeds within the copper coordinative sphere, chiral amine ligand does induce the enantioselective oxidative couplings of phenols such as 2-naphthol [39-41], or 9-phenanthrol [42,43] to form respective atropisomeric... 

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