Divalent copper complexes

In the very recent past, metal complex catalysis has been used with advantage for the stereo- and enantio selective syntheses based on the Henry and Michael reactions with SENAs (454-458). The characteristic features of these transformations can be exemplified by catalysis of the reactions of SENAs (327) with functionalized imides (328) by ligated trivalent scandium complexes or mono-and divalent copper complexes (454) (Scheme 3.192). Apparently, the catalyst initially forms a complex with imide (328), which reacts with nitronate (327) to give the key intermediate A. Evidently, diastereo- and enantioselectivity of the process are associated with preferable transformations of this intermediate. 

The Cupric, Cu2+ or Cu(II) State, 3d9 The most important and stable oxidation state for copper is divalent. There is a well-defined aqueous chemistry of the Cu2+ ion, which generates the familiar blue solution when complexed with water. A large number of copper coordination compounds exist and these have been studied extensively. A strong Jahn-Teller distortion is associated with the 3d9 electronic configuration of this ion. This implies that a regular tetrahedron or octahedron about the Cu2+ ion is never observed, except in the rare occurrence of a dynamic Jahn-Teller effect. The tetragonal distortion about an octahedron can lead to a square-planar coordination which is often observed in Cu(II) oxides. 

The valency of the complex radicle is the same as that of the central metallic atom when the complex contains only ammonia, substituted ammonia, water, or other neutral group. For example, cobalt in eobaltie. salts is trivalent, and the cobalt complex with ammonia, Co(NI13)8 ", is likewise trivalent copper in cupric sulphate is divalent, and the copper complex, [Cu(NH3)4] , is also divalent. In the same wn.y [Co(NH3)5.H30] " and [Co(NII3)4.(II20)2] " are trivalent, as also [Co(NH3)2.en2]" and [Co.en3] ", where en represents cthyleucdiamine, CH NH2... 

Figure 14.4 The three forms of the copper-complexed catenane, each species being either a monovalent or a divalent complex, (a) Four-coordinate complex, (b) five-coordinate complex, and (c) six-coordinate complex.

Since copper is divalent and four-coordinate, it does not give 1 2 complexes. Also, 1 1 azo copper dyes are unstable in solution but are used for dyeing cotton (direct dyes) and occasionally for leather. The important phthalocyanine complexes are regarded as direct dyes (see Section 5.1.6). 

Fig. 13 Principle of the electrochemically induced molecular motion in a rotaxane copper complex. The stable, four-coordinate monovalent complex is oxidized to an intermediate tetrahedral divalent species. This compound undergoes a rearrangement to afford the stable, five-coordinate copper(u) complex.

Fig. 21 The 4-, 5-, and 6-coordinate copper complexes involved. The corresponding Cu(i i)/Cu(i) redox potentials are also indicated. They clearly show the sequence of preferred stabilities for copper(i i) versus copper(i), the hexacoordinate complex producing the most stable divalent complex.

Copper complexes are known in oxidation states ranging from 0 to +4, although the +2 (cupric) and the +1 (cuprous) oxidation states are by far the most common, with the divalent state predominating. Only a relatively small number of Cu complexes have been characterized and the Cu° and oxidation states are extremely rare. A few mixed valence (see Mixed Valence Compounds) polynuclear species have also been isolated examples include a CuVCu species and a Cu /Cu catenane. The coordination numbers and geometries (see Coordination Numbers Geometries) of copper complexes vary with oxidation state. Thus, the majority of the characterized Cu complexes are square planar and diamagnetic, as is common for late transition metals with d electronic configurations. 

Fig. 10. Principle of the electrochemically induced molecular motions in a copper complex rotaxane. The stable 4-coordinate monovalent complex [top left, the black circle represents Cu(I)] is oxidized to an intermediate tetrahedral divalent species [top right, the white circle represents Cu(II)]. This compound undergoes a complete reorganization process to afford the stable 5-coordinate Cu(II) complex [bottom right]. Upon reduction, the 5-coordinate monovalent state is formed as a transient [bottom left]. Finally, the latter undergoes the conformational change which regenerates the starting complex...

The dark blue copper complex formed by reaction of Cu(II) acetate with 5 has the ligand bound in its doubly deprotonated form protons have been lost from two of the pendant arm alcohol groups. This loss of an alcohol proton at each copper site is unusual in the complex of a divalent cation. This is particularly so in the present case because the complex was crystallized at neutral pH. Two O H O bridges are present between the two halves of the bound ligand dimer. Each copper site has a distorted square pyramidal coordination geometry. 

Regiospecific catalytic cydoaddition of alkynes and azides using copper complexes as soluble organic catalysts enables the preparation of divalent and mul-... 

Very little copper is found dissolved in soil solution (49). The divalent copper cation is adsorbed strongly to soil colloids and is relatively exchangeable (50). Copper complexed with soil organic matter is not there in the right form and may be a major reason for copper deficiency in... 

P. L. Vidal, B. Divisia-Blohorn, G. Bidan, J. M. Kern, J. P. Sauvage and J. L. Hazemann, Conjugated polyrotaxanes incorporating mono- or divalent copper complexes, Inorg. Chem., 38, 4203-4210 (1999). 

The originally proposed binding model is consistent with coordination of the divalent copper complex to the 1,2-dicarbonyl moieties in bidentate fashion, making a square planar copper intermediate resulting in... 

Copper quinolinolate (oxine copper) is the chelate of divalent copper and 8-hydroxyquinoline and shares most of its market with copper naphthenate, which is a complex copper salt of mixed naphthenic acids. The principal uses are in wood treatments and some military textiles, where the green color is not objectionable. Copper naphthenate has an odor but is cheaper than oxine. Both copper naphthenate and 2inc naphthenate have performed well in environment tests, with exposure to soil above-ground, as well as concrete (33). 

The effect of the nature of the divalent cation is very pronounced as illustrated in Figure 2 on sample A30. Pectins were found to be much more sensitive to copper than to calcium. A scale of affinity towards divalent cations can be easily obtained this way [18]. This result corroborates what has been measured by pH titration upon addition of increasing amount of cations [28,29], where the order of decreasing selectivity was Pb = Cu Zn > Cd = Ni > Ca. This scale does not follow the size of the radius of the cations but is in agreement with the sequence of complex stability of Irving-Williams [30]. 

Triphenylformazan behaves as a bidentate ligand forming 2 1 complexes (217) with divalent copper, nickel, and cobalt.377 Formazan metal complexes can be compared to complexes of azo dyes or beta diketones due to structural similarity.301,302 In general, formazan metal complexes have low stability toward acids. However, when electron-donating substituents are added to the aromatic ring, a considerable enhancement in stability is observed. Cationic complexes of type 218 are also known. The complexation of formazan with metal cation can be accompanied by oxidation to the tetrazolium salt and the formation of a complex... 

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