Ligand substitution reactions cadmium

Once Cd(CF3)2DME had been isolated, the first experiments with the reagent were devoted to comparing the reactivity of the new compound with that of Hg(CF3)2 in ligand substitution reactions of main group metalloids. The results shown in Eqs. (5)—(8) clearly indicated that at least with Ge and Sn halides, the cadmium-based trifluoromethylating reagent... 

Biirgi studied also a series of five coordinated cadmium complexes, 38, that contain three equatorial sulfur ligands, but in which the fourth and fifth, axial ligands, X and Y, are sometimes iodine, sometimes sulfur, and sometimes oxygen (84). The structural correlations have a clear interpretation in terms of the ligand exchange reaction and are reminiscent of the kind of process that is believed to occur in S 2-type nucleophilic substitution reactions ... 

This reaction was clarified with hexenyl stearate (I) at 60°C during the reaction between zinc stearate and 4-chloro-2-hexene in tetrahydro-furan. During this reaction, zinc stearate reacts immediately with 2 mol of model compound, and kinetic laws do not suggest the presence of CIZnOCOR as an intermediate product in the substitution reaction. Nevertheless, such an organometallic compound was suggested by Frye and Horst (9) and also by Anderson and McKenzie (10) who assumed that such compounds accounted for the ligand exchange between cadmium chloride and barium carboxylate. 

There is an abundant literature on the biochemistry of Cd as a toxic element in a variety of organisms from bacteria to humans. Like all other reactive trace metals, Cd can be toxic simply because of unspecific reactions with protein ligands. For example, reaction of Cd with cysteine thiol groups, for which it has a great affinity, can denature enzymes and make them inactive. More specific toxic effects of Cd result from blockage of certain physiological functions when Cd substitutes for other metals, Ca or Zn, in particular. The ionic radius of Cd and Ca are very similar and cadmium can interfere with Ca metabolism or replace Ca in structural functions [30,31]. 

Because the reactions of related in -cyclohexadienyl complexes are synthetically valuable, the reactions of this ligand have been studied extensively. An outline of how this chemistry can be conducted on the Fe(CO)j fragment is shown in Equation 11.51. A variety of cyclohexadienes are readily available from Birch reduction of substituted aromatics. Coordination and abstraction of a hydride, typically by trityl cation, leads to cationic cyclohexadienyl complexes. These cyclohexadienyl complexes are reactive toward organolithium, -copper, -cadmium, and -zinc reagents, ketone enolates, nitroal-kyl anions, amines, phthalimide, and even nucleophilic aromatic compounds such as indole and trimethoxybenzene. Attack occurs exclusively from the face opposite the metal, and exclusively at a terminal position of the dienyl system. This combination of hydride abstraction and nucleophilic addition has been repeated to generate cyclohexa-diene complexes containing two cis vicinal substituents. The free cyclohexadiene is ttien released from the metal by oxidation with amine oxides. ... 

Reactions of zinc(n) and cobalt(n) complexes of ida, Hida, nta , Eten, and dien with cydta - and Hcydta have been studied. The steric effect of the cyclohexane ring in cydta on the rate of substitution is discussed. Other reports of the replacement of one multidentate ligand by another have appeared for the systems Ni(Hida) + dtpa, Ni(edta-OH) -I- dtpa, and Co(gedta) + (edta-OH) [Hida = A-(2-hydroxyethyl)iminodiacetate, (edta-OH) = lV-(2-hydroxyethyI)ethylenedi-amine-AW A -triacetate, gedta = 2,2 -ethylenedioxybis(ethyIamine)-AAW JV -tetra-acetate). Similar studies of aminopolycarboxylate replacement have appeared for zinc(n), lead(n), and cadmium(n). ... 

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