Trinuclear copper complexes

Biomimetic Oxidations by Dinuclear and Trinuclear Copper Complexes Giuseppe Battaini, Alessandro Granata, Enrico Monzani, Michele Gullotti and Luigi Casella... 

There are many structural studies of copper coordination compounds with azide ligands, mainly of mononuclear and binuclear copper complexes but a few also of trinuclear copper complexes. A comprehensive... 

BIOMIMETIC OXIDATIONS BY DINUCLEAR AND TRINUCLEAR COPPER COMPLEXES... 

Multicopper oxidases are typically active in the catalytic one-electron oxidation of a variety of diphenolic, polyphenolic, enediolic, and aminophe-nolic substrates 1,53,166,167). The mechanism of these reactions is complex and, as discussed in Section I, it involves a sequence of four one-electron oxidations of substrate molecules. The radical products of these reactions undergo dismutation, as shown in Scheme 21 for the oxidation of ascorbate to semidehydroascorbate radical 168,169). The substrate binds to the enzymes close to type 1 Cu, whereas the trinuclear cluster is only accessible to dioxygen, or other small molecules. This situation is clearly difficult to reproduce in a model system and for this reason the type of model oxidation reactions that have been studied so far using synthetic trinuclear copper complexes is more related to the activity of type 3 Cu enzymes than multicopper oxidases. Nevertheless, such trinuclear complexes open new perspectives in stereoselective catalysis, because one of the metal centers... 

Fig. 6. Structure of the octadentate ligands used for the synthesis of biomimetic trinuclear copper complexes.

BorthakurR, AsthanaM, SahaM, Kumar A, Pal AK. An efficient oxidation of alcohols using a new trinuclear copper complex as a reusable catalyst under solvent free conditions. RSC Adp. 2014 4 21638-21643. 

In 1996 Stack and co-workers reported an unusual 3 1 (copper 02 stoichiometry) reaction between a mononuclear copper(I) complex of a A-permethylated (lR,2R)-cyclohexanediamine ligand with dioxygen. The end product of this reaction, stable at only low temperatures (X-ray structure at —40 °C) is a discrete, mixed-valence trinuclear copper cluster (1), with two Cu11 and a Cu111 center (Cu-Cu 2.641 and 2.704 A).27 Its spectroscopic and magnetic behavior were also investigated in detail. The relevance of this synthetic complex to the reduction of 02 at the trinuclear active sites of multicopper oxidases4-8 was discussed. Once formed, it exhibits moderate thermal stability, decomposed by a non-first-order process in about 3h at —10 °C. In the presence of trace water, the major isolated product was the bis(/i-hydroxo)dicopper(II) dimer (2). 

No type III (ii) bent trinuclear copper(II) systems are known, but a number of type III (iii) systems with a symmetrical tridentate bridging ligand to three copper(II) ions are known. In the trinuclear complex, [Cu3(OH)(pao)3](SO4)-10.5H2O (322),703 where pao = 2-... 

Of specific relevance to MCOs are biomimetics that attempt to reproduce the intramolecular electron transfer between a type 1 site and a bi- or trinuclear copper cluster, or model the trinuclear cluster itself Three recent reports exemplify these attempts. Lever and his coworkers synthesized the tetracop-per assembly shown in Figure 5(a) and demonstrated that it was reduced stepwise by 3e Cu(II)-Cu2(II,II)-Cu(II) - Cu(I)-Cu2 (II,II)-Cu(II) — Cu(I)-Cu2 (II,II)-Cu(I) / Cu(I)-Cu2(I,II)-Cu(II) — Cu(I)-Cu2(I,II)-Cu(I). Figure 5(b) illustrates the polarogram for this reduction. EPR spectra were consistent with the reduction scheme proposed and indicated that the last of these 1 e electron transfers was associated with the reduction potential of —0.42 V. In summary, this complex... 

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... 

The Lehn group synthesised the trinuclear copper(I) complex of the substituted 2,2 -bipyridyl/ether derivative 29 and confirmed its helical structure by X-ray diffraction (Figure 6.15). A dinuclear copper(I) complex of 30 (Figure 6.15) was also synthesised and subsequently the corresponding dimeric ethane-bridged bipyridine and phenanthroline ligands were also demonstrated to yield similar di-helicate copper(I) species. These results thus indicate that helicate formation is tolerant towards minor modification of ligand structure. ... 

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