Nickel complexes dithiocarbamates

The nickel(II) dithiocarbamate complexes are neutral, water-insoluble, usually square-planar, species, and they have been studied extensively by a range of physical techniques. The usual methods for the synthesis of dithiocarbamate complexes have been employed in the case of Ni(II), Pd(II), and Pt(II). In addition, McCormick and co-workers (330,332) found that CS2 inserted into the Ni-N bonds of [Ni(aziri-dine)4P+, [Nilaziridinelgf, and [Ni(2-methylaziridine)4] to afford dithiocarbamate complexes. The diamagnetic products are probably planar, but they have properties typical of dithiocarbamate complexes, and IR- and electronic-spectral measurements suggested that they may be examples of N,S-, rather than S,S-, bonded dithiocarbamates. The S,S-bonded complexes are however, obtained, by a slow rearrangement in methanol. The optically active lV-alkyl-iV(a-phenethyl)dithio-carbamates of Ni(II), Pd(II), and Cu(II) (XXIV) have been synthesized, and the optical activity was found to be related to the anisotropy of the charge-transfer transitions (332). 

Nickel(II) dithiocarbamates, Ni(S2CNRR )2, are monomeric, square planar complexes. A less common dinuclear complex is the thiolato bridged [Ni(S2CNHMe)(p-SMe)]2, in which the dimers are self-assembled into tetra-meric supermolecules through weak axial Ni- S secondary bonds.397... 

In view of the conclusion that hydroperoxides are important photo-initiators it is important to evaluate the relative contribution of uv screening, peroxide decomposition, triplet quenching and kinetic chain-breaking to the mechanism of action of typical nickel complex steibilisers. Nickel dibutyl dithiocarbamate (III, R=n Bu, M = Ni) was selected as representative of the peroxide decomposers... 

The crystal structure of bis(NN-di-isobutyldithiocarbamato)nickel(ii). [Ni(S2-CNBu 2)2], shows that nickel is approximately square planar and co-ordinated by two symmetric bidentate ligands (Ni—S = 2.20 A) the ligand symmetry approximates to 2- The reduction mechanism of a series of nickel(ii) dithiocarbamates has been investigated in DMSO at the mercury electrode it is claimed to involve a dissociation to a nickel species which is more easily reduced than the nickel(ii) dithiocarbamate. An e.p.r. study of the reversible electrochemical reduction of nickel(ii) diethyldithio-carbamates in the presence of 2,2 -bipyridyl show that a bipy radical anion is formed initially. Ligand alkylation occurs when ao -dibromo-o-xylene is added to bis-(NiV-diethyldithiocarbamato)nickel(ii). The electron-transfer properties of 16 nickel(ii) dithiocarbamate complexes have been studied in acetone at a platinum electrode. Their oxidation is difficult and irreversible the overall process is ... 

Atsuya I, Itoh K, Ariu K. 1991. Preconcentration by coprecipitation of lead and selenium with nickel-pyrrolidine dithiocarbamate complex and their simultaneous determination by internal standard atomic absorption spectrometry with the solid sampling technique. Pure Appl Chem 63(9) 1221-1226. 

Typical examples of the stabilizers generally used to prevent the above chain reaction are (a) UV absorbers — 2(2-hydroxy-3-tert-butyl-5-methylpheny l)-5-c hi or ob en zo tr ia zo le and 2-h yd ro xy-4-octoxybenzophenone (b) Antioxidants — 3,5-di-tert-butyl-4-hydroxy-toluene and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propa-noate (c) Peroxide decomposers — dilauryl thiodipropionate. In addition quenchers such as the organic nickel complex, Ni(II) bis-(diisopropyl dithiocarbamate) are used for the deactivation of the excited states of the chromophoric groups responsible for light initiation. 

Effective quenchers are based on nickel complexes (phenolate, dithiocarbamate, di-thiophosphate) and are used almost exclusively in polyolefins at a concentration of 0.2-0.5%. Nickel complexes impart a green coloration to plastic articles and their importance was significantly reduced with the introduction of hindered amine light stabilizers (HALS). 

Later work on the reactions of nickel xanthate complexes, [Ni(S2COR )2], with secondary amines revealed the formation of thiourethanes, R2NC(S)OR, together with nickel bis(dithiocarbamate) complexes (Fig. 26). Both are product of nucleophilic attack of the amine at the -hybridized carbon, the difference between the two pathways being whether the alkoxide or metal-sulfide moieties act as the leaving group (225). 

Perhaps the most characteristic feature of transition metal dithiocarbamate complexes are their IR spectra (16, 17, 511). Three regions can be identified (1) the backbone v(C—N) vibration at between 1450 and 1550 cm (2) the v(C—S) vibrations between 950 and 1050 cm (3) v(M—S) vibrations between 300 and 400 cm Variations in v(C—N) and v(C—S) as a function of the substituents are generally quite consistent within a particular class of complex. Some typical values for nickel bis(dithiocarbamate) complexes are given in Table IX. 

R = CF3CH2 C-N 1465 C-S 988 Figure 56. Infrared data (cm ) for some nickel bis(dithiocarbamate) complexes. 

Nickel(II) dithiocarbamate complexes have been known for nearly a century, while since the late 1960s, nickel(TV) complexes have been prepared. These were soon followed by the discovery of nickel(III) complexes, the first crystal-lographically characterized example coming only in 1990 (1465). Most recent work has served to expand these areas, while electrochemical generation of unstable nickel(I) species has also been documented (1466) and the synthesis of a nickel(I) nitrosyl complex has been claimed (379). 

Figure 188. Synthesis of asymmetric nickel bis(dithiocarbamate) complexes ftom pVi(S2CNHR)2].

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