Copper complexes, binuclear, reaction

The reaction of binuclear copper complexes with oxygen as models for tyrosinase activity was also markedly accelerated by applying pressure (106408 ). Tyrosinase is a dinuclear copper protein which catalyses the hydroxylation of phenols. This reaction was first successfully modeled by Karlin and co-workers (109), who found that an intramolecular hydroxylation occurred when the binuclear Cu(I) complex of XYL-H was treated with oxygen (Scheme 5). 

The reaction of dioxygen with laccase or ascorbate oxidase was reviewed in Section IX and in Messerschmidt et al. (74), where the possible binding modes of dioxygen to binuclear and trinuclear copper centers are discussed. A novel mode of dioxygen binding to a binuclear copper complex was found in a compound synthesized by Kitajima et al. (165). The complex contains peroxide in the mode, i.e., side-on between... 

To a solution of the binuclear copper complex of i -N-salicylidene-2-amino-l,l-di(5-ferf-butyl-2-octyloxyphenyl)-3-phenylpropanol (0.30 g, 0.40 mmol copper) in 2,5-dimethyl-2,4-hexadiene (17.6 g, 160 mmol), a solution of /-menthyl diazoacetate (4.5 g, 20 mmol) in the diene (4.4 g, 40 mmol) was added at 40 °C in the course of 7 h. At the beginning of the addition, the reaction mixture was heated to 70 °C to facilitate decomposition of the diazoacetate and thereafter the temperature was maintained at 40 °C. At the end of the addition, a nearly quantitative amount of nitrogen gas had been evolved. 

The binuclear copper complex 4 is also an effective catalyst for enantioselective cyclo-propanation of simple olefins76. The major tram-isomer is produced by the -enantiomer of 4 with predominant (15) configuration. For these reactions the influence of the menthyl ester chirality is not negligible otherwise the relatively high difference in the ee values when the R-or S-catalyst is used cannot be rationalized. Thus, double stereodifferentiation seems to operate to some extent. 

Based on the information on the binuclear copper complex and on the results of how different anions and organic ligands interact with the site, pathways of hydroxylation and oxidation reaction mechanisms of tyrosinase were proposed as shown in Figure 11.6 [18]. The proposed mechanism of action for N. crassa PPO appears to fit the data for most PPOs. The proposed mechanisms for hydroxylation and dehydrogenation reactions with phenols probably occur by separate pathways but are linked by a common deoxy PPO intermediate (deoxy in Figure 11.6). Proposed intermediates in the o-diphenol oxidation pathway are shown in Figure 11.6a. 

The result was quite remarkable. As can be seen from Table 1 most of the alcohols have the same reactivity toward the binuclear copper complex 4. Alcohols bearing hydroxy substituents on their aromatic rings, however, showed a drastically higher reactivity. The reduction rate of complex 4 in the presence of 3,5-dihydroxybenzyl alcohol could not be measured by the technique we used, not even by lowering the reaction temperature to -30 oC. 

Ethers in which at least one group is primary alkyl can be oxidized to the corresponding carboxylic esters in high yields with ruthenium tetroxide. Molecular oxygen with a binuclear copper (II) complex " or PdCVCuCVCO " also converts ethers to esters. Cyclic ethers give lactones. " The reaction, a special case of 19-14,... 

Wall et al. built a binuclear copper(II) complex 43 in order to see acceleration of phosphodiester cleavage (52). With the substrate (50 p.M) shown, the reaction might be considered as a model for the first step of the hydrolysis of RNA, in which the alcohol function of the side chain intramolecularly attacks the Cun-activated phosphate as a nucleophile for a ring closure reaction. Compared to an analogous mononuclear complex 44 (at 1 mM), a rate constant ca. 50 times larger for 43 (at 1 mM) was observed at 25°C and pH 7, implying that the two metal ions probably cooperate. An analogous zinc(II) complex 45 was reported only as a structural model for the active site of phospholi-... 

Sulfur ligands, 633-655 coordination ability, 516 Sulfur monoxide metal complexes instability, 636 Superoxide dismutase, 773 copper complexes, 772 Superoxo complexes, 315-330 binuclear, 323, 325 reactions, 330 bridged... 

The reaction of imidazole-4,5-dicarbaldehyde with 2-aminoethylpyridine in the presence of copper(II) chloride has enabled the preparation of a binuclear complex (equation 2).29 A more common class of binuclear complex is based on template reactions of a phenolic dialdehyde with various amines and includes the copper complexes (14)30 31 and (15).32 Reactions of this type can be extended to the synthesis of macrocyclic binuclear complexes such as (16).33,34... 

Several diverse metal centres are involved in the catalysis of monooxygenation or hydroxylation reactions. The most important of these is cytochrome P-450, a hemoprotein with a cysteine residue as an axial ligand. Tyrosinase involves a coupled binuclear copper site, while dopamine jS-hydroxylase is also a copper protein but probably involves four binuclear copper sites, which are different from the tyrosinase sites. Putidamonooxin involves an iron-sulfur protein and a non-heme iron. In all cases a peroxo complex appears to be the active species. 

Copper(I) complexes similarly react with dioxygen to form peroxo-bridged binuclear complexes.Such complexes do not readily undergo O—O bond cleavage, apparently because the copper(III) oxidation state is not as readily attainable as the Fe(IV) oxidation state in an iron-porphyrin complex. Nevertheless, stable peroxo complexes of copper(II) have been difficult to obtain, because, as soon as it is formed, the peroxo complex either is protonated to give free hydrogen peroxide or is itself reduced by more copper(I) (Reactions 5.42 to 5.46). 

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