Dithiolene complex

The Nature of Molybdenum and Tungsten Centres in Oxo-transfer Enzymes 

Based on the knowledge presently available, it is interesting to speculate on the different roles that have evolved for Mo and W in biological systems. A fundamental aspect is that, for an element to be involved in biology, it must be 

1 A comparison of bond lengths (A) and angles (°) for the M0 sdt)2] M = Mo or W) anions in their (PPh ) saltsf There are no significant differences between the corresponding dimensions of the two 

The significantly greater presence of Mo over W at the catalytic centre of enzymes can be understood by noting the relative concentrations of [MoO ] and [WO ] in seawater. Thus, [MoOJ is present at the relatively high concentration of 1 x 10 mg dm , ca. 100 x the concentration of [W04] . Thus, when these metals are taken up from an aqueous medium where this concentration difference applies, [MoO ] would be expected to be incorporated by an organism in preference to However, the 100-fold excess of 

M0S2 is insoluble in water and, therefore, it would appear that Mo was relatively unavailable for involvement in the early stages of evolution of life on Earth. However, in an oxidising atmosphere i.e. post photosynthesis) M0S2 is converted to [MoO (3). 

---

Metallomesogens. It is also possible to synthesize compounds based on metal atoms which possess Hquid crystal phases. The series based on dithiolene complexes (1), where M = Ni, Pd, or Pt, contains a number of compounds which show the Hquid crystal phases typical of rod-like molecules (13,14). 

The tris (dithiolene) complexes of Mo can be formed by reaction of the corresponding dithiol and molybdate in acid solution. The intense green... 

There has been much discussion about the detailed bonding in 1,2-dithiolene complexes because of the alternative ways that the ring system can be described, e.g. ... 

Figure 15.16 Coordination geometries of bis- and tris-l,2-dithiolene complexes (see text).

Fig. 10. Representation of the mechanism of redox driven K + transport using an electron and a cation carrier. (59-Ni°) and (59-Ni ) are the oxidized and reduced form of the electron carrier, the nickel bis-dithiolene complex 59 [] and [K+] are dicyclohexyl-18-crown-6 and its K+ complex. (Cited from Ref. 59>)...

AuCl3(tht) [129], AuX3[S(benzyl)2)2] (X = Cl, Br) [130] and AuC13 (thian-threne). Various dithiocarbamates and dithiolene complexes have been made, some by oxidation of gold(I) complexes (Figure 4.26). 

The insertion reaction of dimethyl acetylenedicarboxylate (DMAD) into the S-S bond of a cyclic disulfido complex of niobium, Nb(S2)(S2CNEt2)3, takes place to give the corresponding dithiolene complex, Nb S2C2(C02Me)2 (S2CNEt2)3 (Scheme 56) [134]. 

The zinc tetrasulfido complex ZnS4(PMDETA) (PMDETA=pen-tamethyldiethylenetriamine) reacts with alkynes and CS2 to give the dithiolene complexes ZnS2C2(C02Me)2(PMDETA) and ZnS3CS(PMDETA), respec-... 

Fig. 11 The trimeric motif formed upon halogen bonding interaction between the partially oxidized EDT-TTF-I2 and the dithiolene complex [NilmnthF...

A number of structures with S-rich dianion ligands have been determined (297-299).831 832 For example, (297) can be synthesized by the reaction of [Ni(CN)4]2 with polysulfide.833 Upon further reaction with CS2 or substituted acetylenes it forms perthiocarbonato and dithiolene complexes, respectively. 

Several reviews presenting various aspects of dithiolene chemistry have appeared over the years,1015-1026 so that this summary will only focus on some selected findings. Also, the photodissociations of Ni dithiolene complexes, which lead to long-lived Ni complex radicals, have been reviewed.1027 Since many studies in the field of Ni-dithiolene chemistry deal with different oxidation states of the metal, this chapter will also cover much work related to Ni111 and NiIv. 

The most characteristic feature of nickel dithiolene complexes is the existence of an electron transfer series whose members are interrelated by reversible one-electron steps. Three members I-III of the series, I and III being diamagnetic and II having an S= 1/2 ground state, are preparatively accessible [Ni(S2C2R2)2]2 (I) <- [Ni(S2C2R2)2]1 - (II) <- [Ni(S2C2R2)2] (HI). 

Dithiolene complexes with the maleonitriledithiolate (mnt) ligand form highly delocalized systems and are widespread in studies of conducting and magnetic materials. The electronic properties have been extensively studied with various computational methods including Hiickel and extended Hiickel approaches to identify the nature of the orbitals involved in intramolecular and intermolecular interactions. These structural properties allow the complexes to interact in the solid state via short stacking S, S and short interstack S---S contacts.10 4-1048... 

Dithiolene complexes [ Pd(PPh3)2 ra S2C=CCHC(0)R ] are mononuclear or homodinuclear derivatives of ferrocenyl-substituted dithiolene ligands.530 2,2-Diacetyl-1,1-ethylenedithiolato complexes of palladium can be used to prepare dinuclear PdAg and PdAu complexes 531... 

Figure 4.13 Simulation of ESR spectrum of the above cobalt dithiolene complex in frozen toluene at 77 K.

Infrared absorbing nickel dithiolene complexes (68) are also used in certain applications (see Chapter 9.13). However, they are far less durable than the phthalocyanine infrared absorbers.61... 

One of the earliest series of metal complexes which showed strong, redox-dependent near-IR absorptions is the well-known set of square-planar bis-dithiolene complexes of Ni, Pd, and Pt (Scheme 4). Extensive delocalization between metal and ligand orbitals in these non-innocent systems means that assignment of oxidation states is problematic, but does result in intense electronic transitions. These complexes have two reversible redox processes connecting the neutral, monoanionic, and dianionic species. 

---