Complex copper center

The solids were used as catalysts in the benchmark cyclopropanation reaction between styrene and ethyl diazoacetate (Scheme 7). As far as the nature of the clay is concerned, laponite was foimd to be the best support for the catalytic complexes. The best enantioselectivity results (Table 7) were obtained with ligand 6b (69% ee in trans cyclopropanes and 64% ee in cis cyclopropanes) but the recovered solid showed a lower activity and enantioselectivity, which was attributed to partial loss of the chiral ligand from the support. In general, the use of the three chiral ligands led to enantioselectivity results that were intermediate between those obtained in homogeneous phase with CuCl2 and Cu(OTf)2 as catalyst precursors. This seemed to indicate that the sohd behaved as a counterion with an intermediate coordinating abihty to the copper centers. 

Another illustration of the structural changes that may result as a consequence of alkyl substitution at the 3-position of the pyrazolyl group is provided by the structures of the dimeric copper(I) complexes [Tp]Cu 2 (36), [TpMe2]Cu 2 (36), [TpPh2]Cu 2 (37), and [TpBut]Cu 2 (37), which differ in the manner in which the tris(pyrazo-lyDhydroborato ligand bridges the two copper centers (Fig. 16). 

Despite numerous studies involving copper catalysts, only a few isolated copper complexes have been examined, including complexes (155)-(157). Bipyridine,397 phenanthroline,398 and pyridyli-mine cationic complexes399 all exhibit tetrahedral geometries, in which the copper center is bound to two ligands. 

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... 

Copper olefin complexes are usually generated by the direct reaction of a Cu(l) source, the ligand, and the corresponding olefin. Copper ethylene complexes are of interest in view of their biochemical importance,98,98a-98e their applications in organic chemistry,99,99a,99b and industrial applications.100 100 Because of this, many copper alkene complexes have been reported, with different nuclearity, in compounds with one, two, or even three C=C units coordinated to a given copper center. 

TPMA ligand typically coordinates to the copper center in a tetradentate fashion, similarly to Me6TREN [117]. However, the role of counterion coordination (in particular Br and Cl ) in these complexes still remains very unclear. Recently, we were able to isolate and structurally characterize neutral CuI(TPMA)Cl [118] and CuI(TPMA)Br [119] complexes. To our surprise, both complexes were pseudopenta-coordinated (Fig. 6). In CuI(TPMA)Cl, the copper ion was coordinated by four nitrogen atoms with bond lengths of 2.0704(11), 2.0833(11), 2.0888(11) A for the equatorial Cu-N, and 2.4366(11) A for the axial Cu-N bonds, and a chlorine atom with a bond length of 2.3976(4) A. The molecular structure of Cu (TPMA)Br was similar to the structure of Cu (TPMA)Cl and the complex was also found to be pseudopentacoordinated in the solid state due to the coordination of TPMA (Cu-N... 

The size and complexity of the hCP molecule are consistent with a multifunctional role for this protein in the plasma, although its precise functions, as yet, remain unclear for this reason it has been termed the enigmatic copper protein [3], Most of the functions that have been ascribed focus on the presence of the copper centers (see for example refs. 4 and 5), and the major roles can be summarized as follows ... 

The analogous cationic pyridylbis(oxazoline)-copper complexes exhibit square pyramidal geometries in the solid state. As in the bis(oxazoline) series, the triflate is closer to the metal than the SbF6 counterion (2.36 and 2.49 A vs 2.90 A). A single molecule of water is bound to the copper center in the triflate complex 267b, whereas the SbF6 complex 268b accommodates two water molecules in the coordination sphere, Fig. 24 (197). 

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