Carbon disulfide metal complexes

Carbon disulfide forms complexes in which the metal has a low oxidation state with almost every transition metal. The complexes have been reviewed extensively.1 7,8 Three bonding modes are found end-on via S, if bonded and bridging between two metal atoms. The evidence for these three bonding types is largely spectroscopic and therefore limited. CS2 shows a variety of insertion and disproportionation reactions. 

AEROPHINE 3418A promoter is widely used ia North and South America, AustraHa, Europe, and Asia for the recovery of copper, lead, and ziac sulfide minerals (see Elotatton). Advantages ia comparison to other collectors (15) are said to be improved selectivity and recoveries ia the treatment of complex ores, higher recoveries of associated precious metals, and a stable grade—recovery relationship which is particularly important to the efficient operation of automated circuits. Additionally, AEROPHINE 3418A is stable and, unlike xanthates (qv), does not form hazardous decomposition products such as carbon disulfide. It is also available blended with other collectors to enhance performance characteristics. 

Carbon monosulfide [2944-05-0] CS, is an unstable gas produced by the decomposition of carbon disulfide at low pressure ia a silent electrical discharge or photolyticaHy (1 3) ia the presence or absence of sulfur (3). It decomposes with a half-life of seconds or minutes to a black soHd of uncertain composition (1—3). The monosulfide can be stabilized ia a CS2 matrix at — 196°C, and many stable coordination complexes of CS with metals have been prepared by iadirect means (8). 

Other radical reactions not covered in this chapter are mentioned in the chapters that follow. These include additions to systems other than carbon-carbon double bonds [e.g. additions to aromatic systems (Section 3.4.2.2.1) and strained ring systems (Section 4.4.2)], transfer of heteroatoms [eg. chain transfer to disulfides (Section 6.2.2.2) and halocarbons (Section 6.2.2.4)] or groups of atoms [eg. in RAFT polymerization (Section 9.5.3)], and radical-radical reactions involving heteroatom-centered radicals or metal complexes [e g. in inhibition (Sections 3.5.2 and 5.3), NMP (Section 9.3.6) and ATRP (Section 9.4)]. 

The free dithiocarboxylic acids can be isolated, but their salts are preferred. In some cases their metal complexes can be prepared directly by insertion of carbon disulfide into metal-carbon bonds. Thus, the reaction of Grignard reagents, RMgX, with CS2, followed by acid treatment gives the dithiocarboxylic acids RCSSH and metal complexes in good yields.311... 

Characteristic of the heavy metal complexes is their carbon disulfide elimination, yielding mixed thiol-thioxanthato complexes with trimeric structures and thiol bridges.139 The facile nucleophilic substitution of RS by R2N is interesting.113114... 

The formation of complexes of l,2,3,4-thiatriazole-5-thiol has been well described in CHEC-II(1996) 1,2,3,4-thiatriazole-5-thiol can form complexes with various metals such as palladium, nickel, platinum, cobalt, zinc, etc. <1996CHEC-II(4)691>. These complexes can be prepared either by cycloaddition reactions of carbon disulfide with metal complexes of azide anion (Equation 20) or directly from the sodium salt of l,2,3,4-thiatriazole-5-thiol with metal salts. For instance, the palladium-thiatriazole complex 179 can be obtained as shown in Equation (20) or it may be formed from palladium(ll) nitrate, triphenylphosphine, and sodium thiatriazolate-5-thiolate. It should be noted that complexes of azide ion react with carbon disulfide much faster than sodium azide itself. 

Inulin can be modified to compounds that display good heavy metal complexing properties similar to ethylene diamine tetra-acetic acid (EDTA) but with better biodegradation properties (Bogaert et al., 1998). Inulin is first oxidized using sodium periodate to the dialdehyde, and then reduced to a polyol using Pt/C and hydrogen. The polyol can then be modified with carbon disulfide to form xanthate or with S03-pyridine to obtain an inulin sulfate. Alternatively, the dialdehyde can be animated with diaminoethane and sodium cyanoborohydride and the product reacted with monochloroacetic acid sodium salt to form carboxymethylamino inulin. Each of these compounds can be used to precipitate heavy metals. 

The crystal structure of the carbon disulfide adduct of [(C6H5)3P] 3Pt has been solved (42). In this case, the Pt is bound to a carbon and one sulfur of the CS2 group. The Pt atom and its four directly-bound neighbors are coplanar, but the unbound sulfur is tipped out of this plane. Furthermore, the CS2 molecule is bent with a S-C-S angle of 136(4)°. It is an interesting question in this case as to the oxidation state of the metal relative to the geometry of the complex. 

All types of electrophiles have been used with 2-lithio-l,3-dithiane derivatives, including alkyl halides, sulfonates, sulfates, allylic alcohols, arene-metal complexes, epoxides, aziridines, carbonyl compounds, imines, Michael-acceptors, carbon dioxide, acyl chlorides, esters and lactones, amides, nitriles, isocyanates, disulfides and chlorotrialkylsilanes or stannanes. The final deprotection of the dithioacetal moiety can be carried out by means of different types of reagents in order to regenerate the carbonyl group by heavy metal coordination, alkylation and oxidation184 or it can be reduced to a methylene group with Raney-nickel, sodium or LiAIII4. 

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