Mercury complexes cobalt ligands

Many polarographic studies of the reduction of cobalt(II) to form an amalgam at a dropping mercury electrode have been reported, but most of the work has focused on systems involving complexes with ligands other than water [1, 2]. In one of the few investigations of the behavior of Co(H20)6 + (in aqueous 0.1 M potassium nitrate) [3], the following information was deduced ... 

Other metals for which complexes of ligand 79 have been isolated are iron(II)48, 5s, 56,58,59) ir0n(III) 47,52, s4, s6> 59), zinc(II) 57 59), cadmium(II) 59,60,78), mercury(II) 58,78), magnesium(II) S9 60), manganese(II)58>, nickel(II)79), and lead(II)80). The reduction of bis-amws 79 has been reported to afford ligand 81. In addition, the transition metal complexes of iron(III), cobalt(III), nickel(II), and copper(II) with ligand 81 have been prepared and characterized 53). 

Metal ion catalyzed substitutions for the halide (or methyl) ligands of cobalt(III) complexes are well documented (24, 25). Mercury(II) is particularly effective in catalyzing such simple hydrolytic substitutions on Co(III). However,... 

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

There has been some uncertainty concerning the metal content of alkaline phosphatase and the role of zinc in the catalytic process. Early measurements by Plocke et al. (36, 50) showed that there were 2 g-atoms per dimer. The zinc requirement for enzymic activity was demonstrated by the inhibition of the enzyme with metal binding agents in accord with the order of the stability constants of their zinc complexes. It appears that in some cases (EDTA) zinc is removed from the enzyme and in other cases (CN) the ligand adds to the metalloprotein. A zinc-free inactive apoenzyme was formed by dialysis against 1,10-phenanthro-line. Complete activity was restored by zinc only zinc, cobalt, and possibly mercury produce active enzyme. 

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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