Copper complexes mechanisms

Available information on the mechanism of cyclocondensation is rather contradictory. According to one hypothesis, both the condensation of aryl halides with copper acetylides and the cyclization occur in the same copper complex (63JOC2163 63JOC3313). An alternative two-stage reaction route has also been considered condensation followed by cyclization (66JOC4071 69JA6464). However, there is no clear evidence for this assumption in the literature and information on the reaction of acetylenyl-substituted acids in conditions of acetylide synthesis is absent. 

Fig. 20. Attempted mechanism for the arylation catalyzed by the copper complexes...

The degradation of tetrachloromethane by a strain of Pseudomonas sp. presents a number of exceptional features. Although was a major product from the metabolism of CCI4, a substantial part of the label was retained in nonvolatile water-soluble residues (Lewis and Crawford 1995). The nature of these was revealed by the isolation of adducts with cysteine and A,A -dimethylethylenediamine, when the intermediates that are formally equivalent to COClj and CSClj were trapped—presumably formed by reaction of the substrate with water and a thiol, respectively. Further examination of this strain classified as Pseudomonas stutzeri strain KC has illuminated novel details of the mechanism. The metabolite pyridine-2,6-dithiocarboxylic acid (Lee et al. 1999) plays a key role in the degradation. Its copper complex produces trichloromethyl and thiyl radicals, and thence the formation of CO2, CS2, and COS (Figure 7.64) (Lewis et al. 2001). 

In their pursuit of determining solution structures of dinuclear copper complexes as carried out for complex (29) (Section 6.6.3.1.1). Comba reported complex (431) (r = 0.02 Cu-Cu 6.9 A, comparable with the values of 7.2 A predicted by molecular mechanics calculations and 6.7 A obtained from the simulated EPR spectrum).54 They reported369 complexes (432) (square planar) and (433) (Cu-Cu 3.35 A) as well. As part of studying magnetic properties of mono-, di-, and... 

Indeed, the above results seem to point toward a free radical mechanism. Sen and coworkers [60] studied a model copper complex (Fig. 13) and concluded that the polymerization proceeds via a free radical mechanism (Scheme 7) and that the copper complex/MAO system is in fact a new example of a redox free radical generator, in which the role of MAO is to reduce copper(II) to copper completing the redox cycle. This rationale also offers a simple explanation for the observation that very high excesses of MAO are required for the ethylene/acrylate copoly -... 

Scheme 9 Proposed mechanism for regeneration of copper complexes in ARGET and ICAR ATRP...

One example was reported by Tolman and coworkers (78) who found that the copper(I) complex C Tp112 (TpR2=tris(3-(R2)-5-methylpyrazol-l-yl)hydroborate) promotes NO disproportionation via a weakly bound CuITpR2(NO) intermediate (formally a MNO 11 species). The products are N20 and a copper(II) nitrito complex (Eq. (36)). The rate law established the reaction to be first-order in copper complex concentration and second-order in [NO], and this was interpreted in terms of establishment of a pre-equilibrium between NO and the Cu(I) precursor and the Cux(NO) adduct, followed by rate-limiting electrophilic attack of a second NO molecule (mechanism B of Scheme 5) (78b). 

Figure 14. Proposed mechanism and stereochemical model for Nakajima s phenolic coupling using proline-derived copper complexes. [Adapted from (129).]...

Stauber, J. L. and Florence, T. M. (1987). Mechanism of toxicity of ionic copper and copper complexes to algae, Marine Biol., 94, 511-519. 

Figure 4. Copper complexation by a pond fulvic acid at pH 8 as a function of the logarithm of [Cu2+]. On the x-axis, complex stability constants and kinetic formation rate constants are given by assuming that the Eigen-Wilkens mechanism is valid at all [M]b/[L]t. The shaded zone represents the range of concentrations that are most often found in natural waters. The + represent experimental data for the complexation of Cu by a soil-derived fulvic acid at various metakligand ratios. An average line, based on equations (26) and (30) is employed to fit the experimental data. Data are from Shuman et al. [2,184]...

A hydroxoaqua copper complex containing N, N, N, A -tetramethyl-1,2-diamino-ethane (250) is an excellent catalyst for the hydrolysis of sarin, O-isopropyl methylphosphonofluoridate (251), and diethyl p-nitrophenyl phosphate (252 R = Et). The mechanism of the reaction probably involves bound hydroxide attacking the phosphoryl group with concomitant electrophilic catalysis by copper. 

In relation with the ongoing discussion, if Cu in aqueous solution has five or six water molecules in its first coordination shell (9,116,117), it is interesting to compare water exchange rates measured on five-coordinate copper complexes. Rates of water exchange on five-coordinate complexes of copper(II) are drastically reduced from the rate of exchange on aqua ions of copper(II) (Table VII) (113). The mechanism of water exchange is of associative character in all examples studied to date with the exception of [Cu(tpy)(H20)2]. For that complex the water exchange is very rapid compared to the other complexes and the mechanism is a Id. 

Besides, comparisons with other non-macromolecular gelling systems are in progress. Specially, we can co.mpare with a square planar copper complex, which aggregates in linear chains to gelify the cyclohexane (l ). It is immediatly noticed that characteristic times of the aggregation kinetics are correlated to the complexity of the molecular aggregation mechanism involved. 

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