Dithiocarboxylates

The anions of dithiocarboxylic acids, RCS2, have been occasionally used as ligands but their chemistry is much less investigated than that of dithiophos-phates or dithiocarbonates. This may be due to their lower stability, somewhat cumbersome preparation and foul smell. 

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 

The synthesis of alkali metal xanthates from trimethylsilyl dithiocarboxylates and alkali metal fluorides317 has been described as convenient and useful for preparative purposes of metal complexes and organometallic derivatives. 

A selection of metal dithiocarboxylate structures is highlighted. A full picture can be obtained from the reviews cited in Section 1. 

The eight-coordinate vanadium complex V(S2CMe)4 contains both dodecahedral and square prismatic eight-coordinate molecules in the same crystal.322 Of particular interest is the chain-like, mixed valence platinum complex [Pt2(S2CMe)4( i-I)]A, which displays unusual electrical properties metallic conduction between 300 and 340 K and semiconducting properties below 300 K,323 whereas the analogous nickel complex, [Ni2(S2CMe)4(p-I)]x is a semiconductor.324 

---

A -Methylation of the NH of heterocycles using 1 is also known as exemplified by the methylation of indole/ The interesting mechanism is delineated below. O-methylation of weak acids such as phenols, carboxylic acids and oximes as well as 5-methylation such as A -phenylisorhodanine, certain thioketones, and dithiocarboxylic acids have also been reported." ... 

Although deprotonation of simple 1,3-dithiolanes at the 2 position is usually accompanied by cycloreversion to the alkene and dithiocarboxylate, this does not occur for the 2-ethoxycarbonyl compound 55. The anion of this is readily generated with LDA and undergoes conjugate addition to a,(3-unsaturated ketones, esters, and lactones to give, after deprotection, the a,8-diketoester products 56 (73TL2599). In this transformation 55 therefore acts as an equivalent of Et02C-C(0) . 

Similar reaction of dithiocarboxylic acids 75 with 2,4,6-trinitrochlorobenzene (76) in ethanol at 0°C yields thioesters 77, which are then cyclized at room temperature to the final product 78 (77JCS(P1)1273). 2-Oxo- and 2-iminocy-clopentane derivatives 79 provided compounds 80a and 80b, respectively (Scheme 13) (73JCS(P1)1009, 75JCS(P1)1277). 

Dithiocarboxylic acids, their esters and metal dithiocarboxylates. E. Jansons, Russ. Chem. Rev. (Engl. Transl.), 1976,45,1035-1051 (350). 

Cyclopentene-l-dithiocarboxylic acid, 2-amino-meta complexes, 2, 800 Cyclophane chlorophylls, 3, 58 Cyclophane hemes iron complexes, 4,1269 Cyclophosphazenes metal complexes, 2, 81 Cyclopropane carbonylation... 

Dithiobenzoic acid metal complexes, 2, 646 colours, 2, 646 Dithiobiuret metal complexes, 2, 640 Dithiocarbamates chelating resins mineral processing, 6,826 Dithiocarbamic acid metal complexes, 2,585 amine exchange, 1,428 photographic emulsions, 6,98 nickel poisoning, 6,768 tellurium(Il) complexes photothermography, 6,121 Dithiocarbazic acid metal complexes, 2,803 Dithiocarbimic acid metal complexes, 2,588 Dithiocarbimic acid, cyano-metal complexes, 2,808 Dithiocarboxylic acids metal complexes, 2,646 Dithiodiacetic acid metal complexes, 2, 806 Dithiodiketones... 

Julia and coworkers have utilized the sulphenylation reaction in the synthesis of / , y-unsaturated dithiocarboxylates 494, via the reaction sequence shown in equation 298557. 

The chemistry of the dithiocarboxylate complexes of nickel (II) has been investigated extensively. Interest in recent years has been mainly in the further investigation of the "sulfur-rich species, the perthiocarboxylates, and the unusual structures discovered in the dithiocarboxylate complexes (359). The violet complex formed by reaction of [Ni(C H5CS2)2] with sulfur or polysulfide, [Ni(CgHsCS2)2]2, origi-... 

X-Ray structural analysis of [Pt(dithiocumato)2] revealed a dimeric structure containing two bridging and two terminal dithiocarboxylate ligands (XXXII). The proximity of the two platinum atoms (278 pm) suggested that a Pt-Pt bond may be present (415). 

The crystal structure of [Cu(Me2dtc)2] shows that it possesses a center of S3rmmetry, with the copper octahedrally co-ordinated to six S atoms, two Cu-S bonds being longer than the other four (424). Choi and Wasson (425) showed that there is only Cu-S bonding in [Cu(acdc)2] (acdc = 2-amino-l-cyclopentadienyl-l-dithiocarboxylate). 

Addition of lithium dialkylcopper reagents to dithiocarboxylic esters... 

The degradation of CCl4 by Pseudomonas sp. strain KC involved formation of intermediate COCI2 that was trapped as a HEPES complex, and by reaction with cysteine (Lewis and Crawford 1995). Further details of the pathway that is mediated by the metabolite pyridine-dithiocarboxylic acid have been elucidated (Lewis et al. 2001). 

FIGURE 7.64 Degradation of tetrachloromethane (CCI4) mediated by pyridine-2,6-dithiocarboxylate. 

The degradation of tetrachloromethane by a strain of Pseudomonas sp. presents a number of exceptional features. Although was a major product from the metabolism of CCI4, a substantial part of the label was retained in nonvolatile water-soluble residues (Lewis and Crawford 1995). The nature of these was revealed by the isolation of adducts with cysteine and A,A -dimethylethylenediamine, when the intermediates that are formally equivalent to COClj and CSClj were trapped—presumably formed by reaction of the substrate with water and a thiol, respectively. Further examination of this strain classified as Pseudomonas stutzeri strain KC has illuminated novel details of the mechanism. The metabolite pyridine-2,6-dithiocarboxylic acid (Lee et al. 1999) plays a key role in the degradation. Its copper complex produces trichloromethyl and thiyl radicals, and thence the formation of CO2, CS2, and COS (Figure 7.64) (Lewis et al. 2001). 

The degradation of tetrachloromethane by Pseudomonas stutzeri strain KC involves hydrolysis to CO2 by a mechanism involving the natnrally prodnced pyridine-2,6-dithiocarboxylic acid (Lewis et al. 2001) details have already been discnssed in Chapter 7, Part 3. This organism was nsed in field evaluation at a site at which the indigenons flora was ineffective, and acetate was used as electron donor (Dybas et al. 2002). One novel featnre was inocnlation at a series of wells perpendicnlar to the established flow of the gronndwater plnme. Effective removal of tetrachloromethane was snstained over a period of 4 years, and transient levels of chloroform and H2S disappeared after redncing the concentration of acetate. 

Chiari, B., Piovesana, O., Tarantelli, T. and Zanazzi, P.F. (1985) Gold dithiocarboxylates. Inorganic Chemistry,... 

---