Sulphur-Based Ligands

Metallopolymers in which Ni(II) [141-143], Pd(II) [142, 144], and Au(III) [142, 144] are complexed by sulphur-containing ligands are reported in the literature, under the form of dithiols or dithioethers. Side Th groups are suitable to lead to the corresponding metallopolymers. These have been synthesized and characterized, but are not used in electroanalysis. On the other hand, they are often poorly conductive, and p-doping is only obtained at relatively high potentials. 

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Iodide, cyanide, phosphine, sulphur-bearing ligands—soft bases. 

The Suzuki coupling of aryl halides was also extended to tosylates recently. Benzothiazole 5-tosylate reacted with m-xylene-2-boronic acid (6.13.) to give the coupled product in 94% yield using palladium acetate and a stericly congested biphenyl based phosphine ligand as catalyst.17 Another class of less commonly utilised cross-coupling partners are methyltio derivatives. In the presence of a copper salt, which activates the carbon-sulphur bond, 2-methyltio-benzotiazol coupled readily with a series of arylboronic acids.18... 

The first suggestion that the EPR signals could be due to heme iron associated with sulphur ligands is due to Mason (37, 38), basing his conclusions on the general chemistry of the system (4). In a very different set of complexes Roder and Bayer (39) observed that cysteine and its derivatives will interact with a high-spin iron(III) trisethanolamine complex to give a set of EPR g-values not too different from those of P-450 and they too were led toward the conclusion that iron and sulphur were associated in P-450. 

Antimony-sulphur compounds are quite widespread and stable, probably a consequence of soft acid-soft base interaction, and the solid state structures are characterized by the formation of a number of weaker Sb... S secondary bonds. In phenylantimony bis(monothioacetate), the ligands are bonded primarily via sulphur (Sb—S 2.451, 2.471 A), but, as Sb(III) is coordinatively unsaturated, there is substantial secondary interaction with the oxygen atom of the thioacetate (mean Sb...02.81 A) giving a bis chelate structure with antimony in distorted square-pyramidal coordination . The apical position is occupied by the phenyl group and the two sulphur atoms are eis to each other (S—Sb—S 84.8°) in the basal plane. Weak dimers are present in the solid state as a result of Sb... S bonding to the sulphur forming the longer Sb—S bond. 

Methods based on reagents containing sulphur as a ligand atom are less sensitive than those discussed above. Those recommended include DDTC (extraction with benzene or CHCI3) [67-69], in the presence of a surfactant [70,71], thiodibenzoylmethane (cyclohexane, e = 1.2-10 ) [72], thiobenzoylacetone [73], thlo-HTTA [74], and di-2-pyridylketo-thiosemicarbazone [75]. 

Many methods developed are based on organic reagents having sulphur as the ligand atom, such as the dithizone and dithiocarbamates, thio-Michler s ketone (in 30% DMF, e =... 

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