Cobalt mercaptide

Cobalt acetate (Co(COOCCH3)2, Aldrich) and dodecanethiol (CH3(CH2)n)SH, Aldrich, 99- -%) have been used for the synthesis of cobalt mercaptide. Cobalt acetate was dissolved in ethanol under stirring and a solution of dodecanethiol in ethanol was added to this solution drop by drop. Then the precipitate was isolated by vacuum filtration and washed by acetone. Cobalt mercaptide was quite soluble in nonpolar organic solvents and its thermal decomposition gave a pure CoS phase. 

The bridge-forming proclivity of the neutral cobalt (III) complex, CoL3, has also been demonstrated (6). Two trinuclear compounds of the formula [M(CoL3)]Xn, where M is Ni(II) or Co (III), have been isolated in pure form. Detailed study of these substances indicates that the complex CoL3 forms three mercaptide bridges to the third metal ion, thus providing octahedral coordination of the six sulfur atoms about that ion. Data on these unusual compounds are also included in Tables I and II. 

The UV spectra of these complexes are very similar to those found in tetrahedral complexes of Co11 known to have a somewhat distorted geometry, suggesting a similar geometry in the cobalt enzyme.1383 Tetrahedral mercaptide complexes of the type [Co(SPh)4]2- were also shown to have similar absorption characteristics to those of [(LADH)Co2Co2j. This work is in complete agreement with the X-ray crystallographic studies of the native LADH, already mentioned, which shows distorted tetrahedral coordination of both the catalytic and non-catalytic zinc atoms of the enzyme. 

As shown in the second step of Figure 2 orange cobalt-bleomycin A2 was demethylated with a mercaptide and then alkylated at the terminal sulfur atom with a bifunctional chelating agent (4,18). 

The absorption spectrum of cadmium LADH differs markedly from that of the zinc or cobalt enzyme and perhaps bears upon the nature of the metal-binding ligands (Figure 19). An intense band centered at 245 m/i with a molar absorptivity per cadmium atom of 10,200 is shown by the difference spectrum at the bottom of the figure zinc LADH is employed as the reference. Notably, the molar absorptivity of this band is nearly 14,000, close to that reported for the cadmium mercaptide chromophores of metallothionein (23). This is consistent with the hypothesis that sulfhydryl groups may serve as metal ligands in LADH. 

Most mercaptides are not available as commercial products, since large-scale applications of these chemical compounds are quite limited (only mercaptides of tin and antimony are used industrially as thermal stabilizers for poly(vinyl chloride) [de Sousa et al., 2000 Qu L. et al., 2002]). However, these compounds can be synthesized in a very simple way. Owing to their low water solubility, mercaptides can precipitate by reacting thiols (or thiophenols) with aqueous solutions of the corresponding metal salts. In addition to the well-known mercaptides of mercury, lead, zinc, and copper, many others, such as mercaptides of silver, gold, platinum, palladium, iridium, nickel, iron, cobalt, antimony, bismuth, and cadmium, have been prepared. 

Simple transition metal mercaptides, such as Ni(SR)2 or Hg(SR)2, are usually prepared by reactions not involving the thiolate anion as a nucleophile . Occasional use is made of thiolates, for instance in the preparation of chromium(iii) methanethiolate, where sodium methane-thiolate was reacted with chromium chloride in excess of dimethyl disulphide under dry nitrogen and irradiated to yield the desired product, which can also be prepared by other photochemical methods . Cobalt thiolates, [Co(SR)2]n, prepared from cobalt acetate in methanol... 

Further recent papers concerning metal complexes of thio-analogues of j3-diketones deal with the preparation of the cobalt(n) complex of 1,3-diacetylthioacetone, the synthesis and properties of a series of metal complexes of dithioacetylacetone, the synthesis of the nickel(n) complexes of monothio- and dithio-dibenzoylmethane (67) by the nucleophilic cleavage of 1,2-dithiolium salts by hydroxide or mercaptide ions in the presence of nickel(ii) ions, the bromination of the cobalt(m) complex of monothioacetylacetone (68) with iV-bromosuccinimide to yield (69), and the application of monothiodibenzoylmethane as an analytical reagent for quantitative determination of copper. ... 

Y = RS , Cl , Br- I-, CN , PBu 3, PPhg, Se , etc.). Higher alkyl-cobalt derivatives also react with strong nucleophiles, but here olefin elimination occurs rather than nucleophilic displacement. The reaction of iV-alkylcobalamins and A -alkyl cobalt derivatives of five different B12 models with mercaptide ions produces thio-ethers, and it has been found that the relative rates of S-alkylation follow a pattern which is typical of Sn2 displacement rather than a free-radical reaction. 

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