Ligand copper ions with

Van den Berg, C. M. G., and J. R. Kramer (1979), "Conditional Stability Constants for Copper Ions with Ligands in Natural Waters", in E. Jenne, Ed., On Chemical Modeling Speciation, Sorption, Solubility and Kinetics in Aqueous Systems, ACS Symp. Series. 

The use of mixed complex baths is interesting since the concentration of one free metal ion may be altered by varying the amount of one ligand. Thus, in a copper—tin bath, cyanide content may be varied to alter the activity of copper ions, with little or no effect on tin which is present as stannate or as a pyrophosphate complex. It is evident that some knowledge of the coordination chemistry will reduce the degree of empiricism in developing alloy plating baths. 

Conditional Stability Constants for Copper Ions with Ligands in Natural Waters... 

The latter two reactions proceed via the inner-sphere mechanism (see below), that is, they require access of the substrate to the central Cu(I) ion. The disproportionation reaction requires the contact of the central copper ion with a smface, preferably a Cu°(s) surface, as the formation of a Cu° atom is extremely endothermic due to the lattice energy of copper, - 301.4 kJmol (5). Thus ligands that block sterically the approach of a substrate or of a surface to the central copper ion stabilize it (19). An extreme example is 1,4,5,7.7,8,11,12,14,14-decamethyl-l,4,8,ll-tetraazacyclotetradecane, (27). Thus [Cu(I)L ] is stable even in aerated aqueous solutions (27). In analogy, some enzymes with Cud) as the active site, for example, CuSOD, inhibit disproportionation or the reaction with O2 by inhibiting the approach of two Cu(I) central ions to each other which is required for these reactions which are thermodynamically exothermic. 

Evans and co-workers investigated the effect of a number of -symmetric bis(oxazoline) ligands on the copper(II)-catalysed Diels-Alder reaction of an N-acyloxazolidinone with cyclopentadiene. Enantiomeric excesses of up to 99% have been reported (Scheme 3.4). Evans et al." suggested transition state assembly 3.7, with a square planar coordination environment around the central copper ion. In this scheme the dienophile should be coordinated predominantly in an cisoid fashion in... 

Interestingly, the rate constants for Diels-Alder reaction of the ternary complexes with 3.9 are remarkably similar. Only with 2,2 -bipyridine and 1,10-phenanthroline as ligands, a significant change in reactivity is observed. It might well be that the inability of these complexes to adopt a planar geometry hampers the interaction between the copper ion and the dienophile, resulting in a decrease of the rate of the catalysed Diels-Alder reaction. 

The effects of these ligands on the second-order rate constants for the Cu (ligand) catalysed reaction of Ic with 2 are modest In contrast, the effects on IC2 are more pronounced. The aliphatic Oramino acids induce an approximately two-fold reduction of Iv relative to for the Cu" aquo ion. For the square planar coordinated copper ions this effect is expected on the basis of statistics. The bidentate ligands block half the sites on the copper centre. 

Figure 15.2 (p. 412) shows the structure of the chelates formed by copper(II) with these ligands. Notice that in both of these complex ions, the coordination number of copper(II) is 4. The central cation is bonded to four atoms, two from each ligand. 

Catalytically active species derived from 4. Spectrophotometric titration of the backbone ligand of the sngar discriminating dinuclear copper(ll) complex N, N-bis[(2-pyridylmethyl)-l,3-diaminopropan-2-olato] (//-acetato) dicoppeftll) perchlorate (Cu2(bpdpo), 4) in the presence of two equivalents of copper(ll) ions with sodium hydroxide indicates successive replacement of the bridging acetate anion bound in the sohd state with two hydroxyl ions and two water molecnles in alkaline aqneons solntion (eqs. 2 and 3) (20-22). Two species, [Cu2(L h)(OH)] (4a) and [Cn2(L h)(OH)2] (4b), are thus observed in a pH-dependent equihbrium (20). 

Meerwein Arylation Reactions. Aryl diazonium ions can also be used to form certain types of carbon-carbon bonds. The copper-catalyzed reaction of diazonium ions with conjugated alkenes results in arylation of the alkene, known as the Meerwein arylation reaction.114 The reaction sequence is initiated by reduction of the diazonium ion by Cu(I). The aryl radical adds to the alkene to give a new (3-aryl radical. The final step is a ligand transfer that takes place in the copper coordination sphere. An alternative course is oxidation-deprotonation, which gives a styrene derivative. 

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