Chromium thiolate complexes

Haloarene chromium tricarbonyl complexes are activated to nucleophilic attack by thiolate anions [58, 59]. High yields of the thioethers are obtained under liquiddiquid two-phase conditions, but optimum yields are achieved under soliddiquid conditions. In many cases the thioether is produced directly but, where the reaction mixture contains thioether and its chromium complex, the thioether can be isolated by degradation of the complex with iodine or an excess of the thiol. Both 1,2- and 1,4-dichlorobenzenes yield only monothioethers, even when an excess of thiolate anion is used. In contrast, 1,3-dichlorobenzenes produce a mixture of the mono- and dithioethers [59]. Aryl allyl thioethers have been produced under catalysed Heck reaction conditions from S-allyl thiocarbamates and iodobenzene [60]. 

Selected examples of the reaction of haloarene chromium tricarbonyl complexes [Cr(CO)jArX] with thiolate anions... 

The way in which the dominant reduction mechanism for chromate changes with the reaction conditions and how this is related to the toxicity of chromate is not as yet clear. As outlined above, the products of the reaction may depend on the mechanism of reduction and these, as yet, unidentified chromium complexes are probably the agents responsible for the mutagenicity of chromate. The substantial stability of the chromium(V) complexes and thiolate esters generated in the reaction of GSH with chromate suggests that if similar complexes were formed in vivo they would have time to reach many intracellular compartments and could hence be the crucial active intermediates in the toxicity of chromate. 

The complexes responsible for the toxicity have not yet been identified. The possibilities include the thiolate ester, a relatively stable chromium(V) species, or a chromium(III) complex. More work is needed in this area. 

ABSTRACT. The electrochemical oxidation of chromium carbonyl thiolates RSCr(CO)5" has been investigated. Preparative scale oxidation yields the disulfide complex (RSSR)Cr(CO)5 as the major product the mechanism of its formation could be established by cyclic voltammetry experiments the short lived 17 electron radical initially formed undergoes a firagmentation reaction giving the unsaturated pentacarbonyl chromium and the alkylthiyi radical which readily dimerizes. Recombination of these two species gives the product. A slower reaction was shown to take place in the difiiision layer it results in the formation of the binuciear thiolate complex RSCr2(CO)io the redox behaviour of which is presented. 

Brauer, S.L., A.S. Hneihen, K.E. Wetterhahn. 1996. Chromium(VI) forms thiolate complexes with gamma-glutamylcysteine, N-acetylcysteine, cysteine, and the methyl ester of n-acetylcysteine. Inorg. Chem. 35 373. 

The nucleophilicity of coordinated sulfur in the complex [Cr(SCH2CH2NH2)(en)2]2+ towards Mel (equation 51) has been measured in DMF/H20 and compared with sulfur nucleophilicities in thiolatocobalt(III) systems.975 As in the case of the H202 oxidations, the nucleophilicity of thiolate coordinated to chromium(III) is only slightly less than when it is coordinated to cobalt(III), implying that nucleophilic attack by coordinated sulfur does not involve any appreciable distortion in the first coordination sphere of the metal. 

Figure 9-38. The successive oxidation of a thiolate co-ordinated to chromium(in) by hydrogen peroxide to give sulfenate or sulfinate complexes.

Chromium complexes (continued) organohalide activation, 5, 381 with phosphine-based supporting ligands, 5, 365 porphyrin-ligated derivatives, 5, 364 pyridinebis(imine) ligand derivatives, 5, 361 salen-ligated complexes, 5, 379 surface chemistry on oxides, 12, 525 tetradentate [04] compounds, 5, 352 tetradentate thioether derivatives, 5, 365 thiolate-bridged, Fe- and Rh complexes, 5, 308 with Ti(IV), 4, 627... 

Aryl halides may also be reacted with thiolate anions under phase-transfer conditions via activation by formation of tricarbonyl chromium complexes (equation 32)279 280 or other similar arene complexes281,282. 

Chlorophenyl)(2-methoxyphenyl)(4-methylphenyl)bismuthine 23 Chromium tricarbonyl 7r-complexes of triphenylbismuthine 33 Dendretic Biio-bismuthine 25 Dibromo(methyl)bismuthine 203 Dichloro(ethyl)bismuthine 204 Dichloro[2-(isopropoxycarbonyl)ethyl]bismuthine 200 Dimethylbismuth azide 74 Dimethylbismuth thiolates 73... 

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