Toluene-3,4-dithiol metal complexes

A recent review on transition metal complexes of 1,2-dithiolenes summarizes the virtually non-existent literature dealing with silver complexes. Only one general report exists for then-production, which gave complexes of the type [AgL (CI04)] [where n = 1, 2 and L = various thioethers, C2H2(SH)2, C6H4(SH)2, o-MeC6H3(SH)2, maleonitriledithiolate (mnt ) and toluene 3,4-dithiolate (tdt )]. An early report claimed the existence of an ESR-detectable Ag(mnt)2 species however, this could not be obtained free from impurities °... 

The dianion of toluene-3,4-dithiol (TDT2-) forms unique complexes [Mu(TDT)2 ] with transition metals that are readily oxidized via a ligand-centered process to Mm(TDT). 14 Figure 10.4 illustrates the cyclic voltammetry for the latter complexes of Cu, Ni, Co, and Fe. Not only does each Afm(TDT)2 complex undergo a reversible one-electron reduction, but the Ni(III), Co(III), and Fe(III) complexes also exhibit a somewhat reversible oxidation to the M(IV) valence state. For example... 

MoO( dithiolene)J [dithiolene — toluene-3,4-dithiolate (tdt) (60), benzene-1,2-dithiolate (bdt) (61, 62), and quinoxaline-2,3-dithiolate (qdt) (63)]. The [(L-/V( )MoO(bdt)] complex has been structurally characterized and the metal shown to have a distorted octahedral stereochemistry with fac-coordination of (L-A3)... 

The first of these ligands to be used was toluene 3,4-dithiolate (tdt) (lib). Clark used this ligand 6, 7) in 1936 for determining tin. Since that time, tdt has been used by several investigators 3, 5, 23, 28) as a qualitative test for such metals as Mo, W, and Re, but no attempts were made to isolate any of the complexes (much less establish their geometry). The first actual isolation of a complex was by Gilbert and Sandell who made Mo (tdt) 3 22). However, these workers were not able to prepare an analytically pure sample. 

Toluene-3,4-dithiol (dithiol 30) gives complexes with many metals (e.g. Bi, Sb , Co, Cu, Ni and Pb in acid solution Mn, Fe, Tl, V and Ru in alkaline, aqueous pyridine solution). The yellow-green tris complex with molybdenum can be separated from tungsten(VI) by extraction into pentyl acetate from 3.7 M HCl. The blue-green tungsten complex extracts if the acidity is lowered. Sn also gives a yellow-red complex. 

The polarographic reduction of a number of InL complexes (L = toluene-3,4-dithiolate) [InL2D] (D = phen, bipy, etc.), InLl" (L= l,2-dicyanoethylene-l,2-dithiolate), etc., in non-aqueous solution demonstrated a series of reversible one-electron changes corresponding formally to In ->In In - In°, in contrast to the In - In° reduction observed in aqueous solution. As noted above (Section 25.2.3.3), the formal oxidation states are assigned to the metal on the assumption that the ligand itself is not reduced, and this remains to be confirmed experimentally. 

In addition to these reactions, metal ions and ligands may participate in many other equilibria reactions such as complex formation, protolysis, and hydrolysis reactions. In order to transfer metal ions quantitatively into the organic phase, the extraction conditions (pH, reagent concentrations, volume ratio of the liquid phases) must be optimized. Figure 146 represents the response of molybdenum as a function of pH in three different organic solvents with toluene-3,4-dithiol and 8-hydroxyquinoline as ligands. According to this plot the determination of molybdenum is most sensitive in MIBK... 

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