Cobalt dithiocarbamate complexes

Cobalt dithiocarbamate complexes are now known in oxidation states - -1 to +4, the first reported examples being the tris(dithiocarbamate) complexes [Co(S2CNR2)3], which were prepared in 1920 (1388). 

Lead, mercury, cadmium and cobalt dithiocarbamate complexes are all oxidized at very much more positive potentials than Cu(dtc)2. A potential of +0.95 V vs Ag/AgCl can be used for the determination of cobalt. Careful selection of the applied potential, JSapp, to avoid the ligand-based thiuram disulfide (background) response enables the determination of lead (Eapp = +0.80 V vs Ag/AgCl) and cadmium (E pp = +0.90 V vs... 

The alleged preparation of the supposed cobalt(II) complex Na[Co(Et2dtc)3] described by D Ascenzo and Wendlandt (305) has been repeated by Holah and Murphy (306), who identified the product as [Co(Et2dtc)3]. Complexes of cobalt(III), nickel(II), and palladium(II) salts with cationic, dithiocarbamate ligands have been synthesized (307). Reaction of the secondary amine (Et2N(CH2)2)2NH with CS2 produces... 

Cobalt(III) complexes of formula cis- and trans-[Co(dtc)L4]2+ and [Co(dtc)2L2]+ where dtc = dimethyl-, diethyl- or piperidino-dithiocarbamate were prepared with phosphites P(OMe)3, P(OEt)3 and 4-ethyl-2,6,7-trioxa-l-phophabicyclo[2.2.2]octane as ligands L.1048 Whereas Co—P bonding is found, as defined in the crystal structures of each of the two forms of complexes isolated, a linkage isomer in which the phosphite is O bound was detected for the bis(dithio-carbamate) compounds. 

It is apparent that the coordination geometry at the cobalt atom is distorted octahedral. The cyclopentadienyl rings of the phosphinoferrocene fragment are staggered and tilted towards the cobalt atom (by 4.4° in the acetylacetonate complex and by 5.0° in the dithiocarbamate complex). 

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. 

It is not clear when dithiocarbamates were first prepared, but certainly they have been known for at least 150 years, since as early as 1850 Debus reported the synthesis of dithiocarbamic acids (1). The first synthesis of a transition metal dithiocarbamate complex is also unclear, however, in a seminal paper in 1907, Delepine (2) reported on the synthesis of a range of aliphatic dithiocarbamates and also the salts of di-iTo-butyldithiocarbamate with transition metals including chromium, molybdenum, iron, manganese, cobalt, nickel, copper, zinc, platinum, cadmium, mercury, silver, and gold. He also noted that while dithiocarbamate salts of the alkali and alkali earth elements were water soluble, those of the transition metals and also the p-block metals and lanthanides were precipitated from water, to give salts soluble in ether and chloroform, and even in some cases, in benzene and carbon disulfide. 

Bond and co-workers (303, 540,541) also utilized (ESMS) to study Ugand-exchange reactions. For example, while cobalt(III) tris(dithiocarbamate) complexes are inert to substitution and exchange reactions, they do undergo ligand exchange at elevated temperatures and upon controlled-potential oxidation and reduction (Fig. 59) (541). 

Figure I74 Examples of linked cobalt(III) tris(dithiocarbamate) complexes.

In a series of papers, Siddiqi et al. detail the synthesis of purported cobalt(lI) complexes, [Co(S2CNR2)2], derived from a range of amines including succi-nimide and phthalimide (49), p-naphthylamine (1125), and chloroanilines (1423). Others have claimed the preparation of those containing benzyl (506) and benzylpiperazine (1126), substituted piperidines (1116,1424,1425), and 1,3,4-thiaxolyl dithiocarbamate (1426). In none of this work was oxygen rigorously excluded. 

Bis(2-hydroxyethyl)dithiocarbamate complexes of a range of metals including cobalt, chromium, nickel, copper, and platinmn have been separated by... 

The simultaneous determination of cobalt and nickel in aqueous solutions as trifluoroethyl dithiocarbamate complexes is possible down to 10 ppb in the presence of a 10-fold excess of iron, copper, cadmium, and zinc (1434), while the same dithiocarbamate is used for the determination of cobalt in urine samples by GC and MS (1435). 

The groups of both Stephenson (1442) and Maitlis and co-workers (1443) independently prepared pentamethylcyclopentadienyl complexes [Cp M(S2CN- 2)2] (M = Rh, Ir R =Me, Et) upon addition of 2 equiv of dithiocarbamate salt to [Cp MCl(p-Cl)]2. Like the analogous cobalt cyclopentadienyl complexes, they contain both a monodentate and a bidentate dithiocarbamate [Cp Rh(S2CNMe2)2] (319) (Fig. 180) is characterized by the v(C—N) vibrations spectrum at 1392 and 1530 cm , respectively, in the IR spectrum. In solution, interconversion of the two dithiocarbamates occurs (Fig. 180). The NMR line shape analysis suggests that it occurs via a dissociatively controlled intramolecular mechanism. 

The bis(dithiocarbamate) complex derived from the alkaloid emetine (Eq. 163) can be detected at 10 °-10 mol dm by flow injection analysis using the electrogenerated chemiluminescence detection of [Ru(bpy)3] " (1761). Further, the copper, nickel, and cobalt emetine-derived complexes have been successfiiUy separated and detected to a limit of 50 uM by using this method (1762). 

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