Iron-sulfide-thiolate systems

Judging from the ease with which models of Fc4S4 are prepared under a variety of conditions and their relative stability, the Fe4S4 " core structure seems to be a relatively stable entity, a local thermodynamic minimum in the multitude of possible iron-sulfide-thiolate complexes. The initial preparation and structural characterization of the models showed that synthetic chemistry can duplicate the biological centers in far-simpler chemical systems, which can be more easily studied in great detail. 

A chemistry of cobalt-sulfide-thiolate molecular clusters comparable with that of iron systems has also begun to emerge. Treatment of [Co4( -SPh)6(SPh)4]2- with HS- in acetone affords the octanuclear cluster [Co8(ji4-S)6(SPh)8]4 isolated as its Pr4N+ salt.988 In MeCN solution the complex is red-purple with intense sulfur-core charge transfer bands which obscure the Co" d-d transitions. This behaviour contrasts with that of both mono- and poly-nuclear cobalt"-thiolate complexes, which all display LMCT bands below 440 nm and have well-developed v2 and v3 features. The [Co8(/j4-S6)]4+ core sustains reversible one-electron oxidation and reduction (E]l2 = —0.54, — 1.18 V, MeCN) and chemical reduction with sodium acenaphthylenide in THF gives [Co8(/r4-... 

Iron porphyrins have been studied extensively over the past 30 + years as model systems of cytochrome P450.13 Biomimetic model studies included variants in axial ligands (thiolate and other bases), the oxidation of alkanes, olefins, sulfides, and amines, and utilization of several oxidants such as hypochlorite (bleach), iodoso-benzene (ArlO), hydrogen peroxide, and organic peroxides (ROOH). The first-generation models employed the mevo-tetraary I porphyrins (Figure 3.5). These were... 

A well-known example of a complex catalytic reaction that takes place on the surface of carbon is the oxidation of hydrogen sulfide [329,330], When water is present on the carbon surface and the surface has the basic pH required for dissociation of H2S, oxidation of the HS ions by active oxygen occurs either to elemental sulfur or sulfuric acid. The latter is formed when the reaction takes place in very small pores, where only sulfur radicals very susceptible for further oxidation to SO3 are formed. Catalytic oxidation also occurs in the case of methyl mercaptan adsorption [331], where on basic carbon, thiolate ions formed as a result of dissociation are further oxidized to dimethyldisulfide strongly adsorbed in the pore system. In the case of desulfurization, inorganic constituents of carbon such as iron and calcium also play a crucial role. Those elements, present even in small amounts, contribute significantly to the oxidation reactions as catalysts [332,333],... 

The all-sulfide P -type cores replicate the overall structure of the P framework, albeit with p2 Sulfide and molybdenum in place of the p2 thiolate and end iron atoms in the biological cluster.The unusual and characteristic distorted trigonal prismatic pg-sulfide ligand is reproduced faithfully, although the bend at the common vertex is more pronounced in the synthetic systems as measured by exterior, non-rhomb Fe-(pg-S)-Fe angles... 

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