Ligand substitution reactions mercury

Mercury(II) is known to accelerate Ligand Substitution reactions of complexes of formnla ML5X (M = Rh, Cr, Co, Ru L = H2O or NH3 X = bridging halide or psendohalide), probably by forming an intermediate with a halide bridge between Hg and M. 

Once Cd(Cp3)2DME had been isolated, the first experiments with the reagent were devoted to comparing the reactivity of the new compound with that of Hg(Cp3)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 was much superior to the mercurial 31) ... 

Aromatic ketones arylations, 10, 140 asymmetric hydrogenation, 10, 50 G—H bond alkylation, 10, 214 dialkylzinc additions, 9, 114-115 Aromatic ligands mercuration, 2, 430 in mercury 7t-complexes, 2, 449 /13-77-Aromatic nitriles, preparation, 6, 265 Aromatic nucleophilic substitution reactions, arene chromium tricarbonyls, 5, 234... 

These structure determinations show that thioethers and saturated cyclic sulphur compounds do not form addition compounds with HgCI as has previously been believed. The complexes formed are the result of a substitution reaction, in which one of the chlorine atoms in HgCl has been replaced by the sulphur atom of the donor molecule giving rise to positively charged mercuric complexes and negative chloride ions. The configuration of ligands around mercury in these complexes is intermediate in character between that of tetrahedrally and octahedrally coordinated mercury. 

The above reactions in this section have been examples of addition alone or addition followed by elimination. Ligand reactions involving nucleophilic substitution are also known and these are of the dealkylation type. Lewis acids such as aluminum chloride or tin(IV) chloride have been used for many years in the selective demethylation of aromatic methyl ethers, where chelation is involved (Scheme 27). Similar cleavage of thioethers, specially using mercury(II) salts, is commonly used to remove thioacetal functions masking ketones (equation 27).104 In some cases, reactions of metal ions with thioether ligands result in isolation of complexes of the dealkylated organic moiety (equations 28 and 29).105-107... 

The chloro[exo-5-acetoxytricyclo[2.2.1.0 ]hept-enifo-3-yl]dipyridinepalladium complex 17 [prepared from norbornadiene and palladium(II) chloride bisbenzonitrile complex with subsequent substitution and ligand exchange ] underwent exchange with acetoxy(phenyl)mer-cury, analogous to the known exchange reactions between palladium(II) chloride or acetate and phenylmercury salts, to afford a mixture of products, including biphenyl (54%), exo,exo-3,5-diacetoxytricyclo[2.2.1.0 ]heptane (19,20%) and chloro[exo-5-acetoxytricyclo[2.2.1.0 ]-hept-e Jo-3-yl]mercury (18, 57%). 

The mechanism of 1 1 complex formation between palladium(II) and catechol and 4-methylcatechol has been studied in acidic media, and the rate of 1 1 (and 1 2) complex formation between silver(II) and several diols is an order of magnitude higher in basic solution than in acidic. The kinetics of formation and dissociation of the complex between cop-per(II) and cryptand (2,2,1) in aqueous DMSO have been measured and the dissociation rate constant, in particular, found to be strongly dependent upon water concentration. The kinetics of the formation of the zinc(II) and mercury(II) complexes of 2-methyl-2-(2-pyridyl)thiazolidine have been measured, as they have for the metal exchange reaction between Cu " and the nitrilotriacetate complexes of cobalt(II) and lead(II). Two pathways are observed for ligand transfer between Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II) and their dithiocarbamate complexes in DMSO the first involves dissociation of the ligand from the complex followed by substitution at the metal ion, while the second involves direct electrophilic attack by the metal ion on the dithiocarbamate complex. As expected, the relative importance of the pathways depends on the stability of the complex and the lability and electrophilic character of the metal ion. 

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