Transition metals, dithiocarbamate complexes

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. 

It should be acknowledged that both before and after Coucouvanis s reviews (16, 17) others also reviewed aspects of transition metal dithiocarbamate chemistry (18-31). Notably, in 1984 Bond and Martin reviewed the electrochemical and redox behavior of transition metal dithiocarbamate complexes (20), and as such less emphasis is placed here on electrochemical properties. Further, as early as 1965, Thom and Ludwig produced an excellent book The Dithiocarbamates and Related Compounds (32), which is still well worth a read, especially for the newcomer to the area. 

This chapter is aimed at inorganic chemists and as such it focuses on the synthesis, properties, and reactivity of transition metal dithiocarbamate complexes. A flavor of the established and potential applications of each metal type is given in Section IV, but space restrictions nessetate that their applications in analytical chemistry and the agricultural industry (27), together with their widespread biological applications (45—48) are not fully developed. 

Transition metal dithiocarbamate complexes were probably first prepared in 1907 by Delepine (2) and over the following century, dithiocarbamate complexes of all the transition elements have been prepared and in a wide range of different oxidation states (Table 1). Perhaps most impressive is their ability to stabilize molybdenum in seven oxidation states ranging from - -6 to 0 (Fig. 24). 

While transition metal dithiocarbamate complexes can be prepared in a wide variety of ways, by far the most common is the direct ligand addition, which often, but not necessarily, results in loss of a coordinated anionic ligand, and sometimes a second neutral ligand also (Eq. 13). This route has few limitations and complexes of all the transition metals have been prepared using it. 

Casey and Vecchio (186,187) developed the oxidative-addition of thiuram disulfides to metals in order to produce a one-step preparation of a wide range of transition metal dithiocarbamate complexes. In this way, [Ni(S2CNMe2)2] and [Zn(S2CNMe2)2] can be prepared in near quantitative yields. With copper, only the copper(II) species are seen, and this is in keeping with Akerstrom s (188) earlier observation that copper(I) species react instantaneously with thiuram disulfides to generate the analogous copper(II) complexes. 

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. 

The thermochemistry of dithiocarbamate complexes is of considerable interest, primarily since they can be used as molecular precursors for the synthesis of a range of technologically important metal sulfides, especially those of copper and zinc (see Sections III.H.l.g.ii and III.I.Lh.i). The successful application of this approach relies on the volatility of the metal complexes and the strength of the metal-sulfur and metal-carbon bonds since the latter must be cleaved, while the former is retained (at least to some extent). Consequently, a large number of studies have focused on the thermochemical properties of transition metal dithiocarbamate complexes and HiU and co-workers (22, 562, 563) and others (23, 564) reviewed aspects of these. 

Hopefully, this chapter has served to illustrate the tremendous diversity of the dithiocarbamate ligand. While it is over a century since the first transition metal dithiocarbamate complexes were prepared, exciting new developments are still being made, and we can look forward to more in the future. 

Mdssbauer spectra of bonding and structure in, 15 184-187 reactions with diborane, 16 213 stabilization of, 5 17, 18-19 cyanates, 17 297, 298 cyanide complexes of, 8 143-144 cyclometallated bipyridine complex, 30 76 diazene complexes, 27 231-232 dinitrogen complexes, 27 215, 217 diphosphine complexes of, 14 208-219 dithiocarbamates, 23 253-254 -1,2-dithiolene complexes, 22 323-327 hydrogen bonding, 22 327 halide complexes with phosphine, etc., 6 25 hexaflouride, structure, 27 104 hydride complexes, 20 235, 248-281, see also Transition metal-hydride complexes... 

Similarly, nickel(ll) and copper(ll) transition metal dithiocarbamate ion-pair receptors 21, containing amide-and crown ether-recognition sites, bind alkali metal cations and various anions. The sandwich K+ complex of the nickel(ll) receptor cooperatively enhanced the binding of acetate anion, while the copper(ll) receptor electrochemi-cally can sense anions and cations via perturbation of the copper(n)/copper(m) dithiocarbamate redox couple <2002JSU89>. 

Abstract - The temperature dependence of the proton nmr spectra of dithiocarbamato iron(III) complexes is markedly solvent dependent. A study is made of the temperature dependence of the nmr shifts for the N-CH2 protons in tris(N,N-dibutyldithiocar-bamato) iron(III) in acetone, benzene, carbon disulfide, chloroform, dimethyIformamide, pyridine and some mixed solvents. This contribution shall outline first how the nmr shifts may be interpreted in terms of the Fermi contact interaction and the dipolar term in the multipole expansion of the interaction of the electron orbital angular momentum and the electron spin dipol-nuclear spin angular momentum. This analysis yields a direct measure of the effect of the solvent system on the environment of the transition metal ion. The results are analysed in terms of the crystal field environment of the transition metal ion with contributions from (a) the dithiocarbamate ligand (b) the solvent molecules and (c) the interaction of the effective dipole moment of the polar solvent molecule with the transition metal ion complex. The model yields not only an explanation for the unusual nmr results but gives an insight into the solvent-solute interactions in such systems. 

In this paper we shall extend our earlier interpretation of the redox results to the nmr data for the N - CH2 protons in tris(N,N-diethyldithiocarbamato) iron(III). We shall show that the solvent dependence of the nmr shifts can be interpreted as arising from solvent interactions with the iron(III) dithiocarbamate system. Although the solvent interactions are small compared with the electronic interactions within the transition metal iron complex the effect is marked since in these cases for the d iron system there are low lying electronic states where the energy separation is sensitive to small changes in the crystal field environment of the transition metal ion. 

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