Copper compounds dinuclear complexes

NHC ligands with a pendant group that enforces chelation have also been coordinated to copper centers. The reaction of Cu20 with pyridine fV-functionalized carbene ligand led to the formation of several compounds.91 In the case of mesityl derivatives, a dinuclear complex with a weak metal-metal interaction was isolated 60,91 whereas for the bulkier 2,6-diisopropylphenyl group, a monomeric complex was formed and characterized 61 (Figure 25).91... 

The dinuclear complex [Cu2 (Ls)2] has also been synthesized and isolated (217). In tetrahydrofuran (THF) solution, this species is oxidized by air yielding the diamagnetic, dinuclear deep green (phenoxyl)copper(II) complex [Cu2(Ls )2]X2 (X = C1,C104) as microcrystalline solid and H202. Although both compounds have... 

The dimerization of the copper complex takes place to form the bis-Cu(II) compound 3, where the phenolate anion is the bridging ligand, just as proposed by Karlin [75], in the dinuclear complexes that act as the actual catalyst in the active state. 

The majority of cyanide-bridged dinuclear complexes described for the combination of metal ions belong to the biologically relevant class of Cu —Fe dimers. These compounds serve as models for the binuclear cyanide-inhibited site of cytochrome c oxidase, an enzyme that contains the heme-copper active site responsible for the O2 reduction chemistry (59). The lethal toxicity of cyanide was traced to its irreversible binding and inhibition of this active site in the enzyme (60). The biologically relevant aspects of these complexes were the subject of many reports (61,62). Our interest is in describing their crystal structure, which will be correlated to the magnetic properties in a later section. 

The Cu(/i-dmpz)2Cu core in Complex 33 was found in an uncommon planar conformation. The related compound [(RNC)Cu(pz)]2 was obtained from [Cu(pz)] (2a or 2b isomers) (13) on treatment with RNC (50). Dinuclear copper(I)-cyclohexylisocyanide complexes were also obtained by reacting [Cu(dcmpz)] (27) or [Cu(dppz)]4 (17) with RNC. The Complex [(RNC)-Cu(dcmpz)]2, 34, is topologically equivalent to the dmpz analogue 33 however, the pattern of bond distances and angles of the Cu—(N—N)2—Cu ring, as well as its conformation, is markedly different (27). The X-ray crystal structure of [(RNC)Cu(dppz)]2, 35, was reported and the results were compared with those of the parent Complexes 33 and 34 (17). Complex 35 possesses a Cu—[N—N]2—Cu ring in a chairlike conformation, which has only a few precedents (51-53) (Fig. 6). 

The rate law, rate constants, and activation parameters have been obtained for exchange of trifluoroacetate with its dinuclear molybdenum(ii) complex [M02-(OaCCFa). The results are discussed with particular reference to related dimolybdenum and dirhenium metal-metal-bonded compounds. A preliminary report on copper(ii) exchange with copper(ii)-salen complexes gives evidence to support the hypothesis of the intermediacy of dinuclear species. ... 

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. 

Theoretical studies by Pyykkb in 1998 for [M2(NHCHNH)2] systems, M=Cu, Ag, and Au, predicted the M-M distances at the MP2 level [8]. Experimentally, systems containing amidinate ligands were known with Cu and Ag but unknown with Au. The results for the models containing silver and copper are close to the X-ray structures of [M2(ArNC(H)NAr)2], Ar=C6H4-4-Me and M=Ag, Cu. The Ag-Ag distance is 2.705 and 2.712 A and the Cu-Cu distance is 2.497 and 2.528 A at the experimental and theoretical level. Table 1.1. The hypothetical dinuclear gold(I) amidinate compound was calculated to have an Au-Au distance at the MP2 level of 2.728 A [8]. The dinuclear gold(I) amidinate complex now known proves the predicted Au-Au distance to be rather good. 

---