Clusters metal sulfides

The red tetrathiomolybdate ion appears to be a principal participant in the biological Cu—Mo antagonism and is reactive toward other transition-metal ions to produce a wide variety of heteronuclear transition-metal sulfide complexes and clusters (13,14). For example, tetrathiomolybdate serves as a bidentate ligand for Co, forming Co(MoSTetrathiomolybdates and their mixed metal complexes are of interest as catalyst precursors for the hydrotreating of petroleum (qv) (15) and the hydroHquefaction of coal (see Coal conversion processes) (16). The intermediate forms MoOS Mo02S 2> MoO S have also been prepared (17). 

Palladium dimethylsilanedithiolato complex is a precursor for Ti—Pd and Ti—Pd2 heterometal-lic complexes.311 The bis-silyl sulfides (R3Si)2S have been widely used to prepare a variety of metal sulfide clusters, because these reagents exploit the strength of the Si—O and Si—Cl bond to... 

With other transition metal sulfides the mixed vanadium-silver cubane-like cluster, (Et4N)2[Ag2V2S4 S2CN(OC4H8)2 2(SPh)2] (166)1092 and [ y-C5Me5)WS3 2Ag3 (PPh3)3]N03 (167), have been reported.1093... 

In a series of papers, metal sulfide cluster anions of first-row transition metals, principally copper, have been reacted with a variety of reagents including thiols, sulfur, phosphorus, and phosphines (99, 145, 256, 257). 

The reactions of P4 with the metal sulfide cluster anions has been extended to Ni, Co, and Fe (99). The copper sulfide cluster anions were generally the least reactive anions toward P4 with similar anions having reactivities [NinSJ > [Co SA ... 

Photoelectron spectroscopy has been used to determine the threshold of electron detachment in small cluster anions and in some cases electronic transitions may be observed. The group of Nakajima and co-workers (261-264) studied several metal sulfide cluster anions. Many other systems have been studied by photoelectron spectroscopy including the [LaCJ (265), [AuC6F6] (266), and mixed-metal cluster anions (267). 

Lack of reactivity in copper sulfide cluster anions has been associated with structural features such as linear S-Cu-S bonding. Reactivity of metal sulfide cluster anions is associated with exposed under-coordinated metal atoms able to bond to coordinating molecules this is the essence of this chapter. 

K), Fe-S cluster assembly (nIfM) and the biosynthesis of the iron molybdenum cofactor, FeMo-co (nifN, B, E, Q, V, H)(5a). It is the last two functions, involving the placement of unusual transition metal sulfide clusters into the nitrogenase proteins, that cause nitrogenase and its components to be appropriately included in this symposium. 

This caveat notwithstanding, the Dominant Hypothesls( ) designates [FeMo] as the protein responsible for substrate reduction. The FeMo protein contains an 02fi2 subunit structure due to expression of the nifD and nlfK genes(24,25). Its overall M.W. of about 230,000 reflects the 50-60,000 M.W. of each of its four subunits. The nonprotein composition of 30 Fe, 2 Mo, and 30 s2- betokens the presence of transition metal sulfide clusters, which are presumed to be the active centers of the protein. 

Semiconductor clusters were prepared via multifunctional 116 inorganic-organic sol-gel processing. The reaction of hexamethyldisilylthiane with metal alkoxide (in THF + alcohol) produced silane functionalized metal sulfide clusters and inorganic/organic network formers. 

Other metal complexes such as 2,2 -bipyridine complexes of Rh and Ir are efficient electrocatalysts for the reduction of C02 in acetonitrile.134 In the production of formate the current efficiency is up to 80%. Electrochemical reduction catalyzed by mono- and dinuclear Rh complexes affords formic acid in aqueous acetonitrile, or oxalate in the absence of water.135 The latter reaction, that is, the reduction of C02 directed toward C-C bond formation, has attracted great interest.131 An exceptional example136 is the use of metal-sulfide clusters of Ir and Co to catalyze selectively the electrochemical reduction of C02 to oxalate without the accompanying disproportionation to CO and CO2-. 

Figure 24-3 Structures of the metal-sulfide clusters of the MoFe-protein.

Several additional proteins identified as necessary for metal-sulfide cluster formation are present in bacteria and in eukaryotes, both in the cytosol and in mitochondria. They may serve as intermediate sulfur carriers, as scaffolds or templates for duster formation, or for insertion of intact Fe-S, Fe-S-Mo, or other types of clusters into proteins468 473f and into 2-selenouridine473g (see also p. 1617). Sulfurtransferases are also thought to be involved in insertion of sulfur atoms into organic molecules such as biotin, lipoic acid, or methanopterin.474... 

The interconversions of the numerous aggregates in the Fe/S/SR systems have been successfully described from measurements of electronic spectra and H NMR.141>212 It is evident that some clusters such as [Fe4S4(SR)4]2 have thermodynamic advantage similarly, in the Cd/S/SPh system, [S4Cdl0(SPh)16 4 predominates, and M2+ + H2S + PEt3 reactions yield stable aggregates [SJMm(PEt3)tt]2+ instead of metal sulfides.52-250... 

Our knowledge concerning soluble metal complexes with sulfide ions as ligands has increased considerably during the last two decades and this kind of Compound is still of topical interest. Some of the reasons for this are the development of a very flexible and fascinating structural chemistry of multinuclear metal-sulfur complexes, the fact that the active sites of some electron transfer proteins contain metal ions and labile sulfur,41,42 and also the relation of metal-sulfur cluster compounds to some heterogeneous catalysts. In addition, apart from the numerous binary and ternary sulfides which occur in nature, we have at our disposal a rich solid state chemistry of metal sulfides, which has been reviewed elsewhere and will be excluded here.43"17... 

Dihydro-277-l-benzothiopyran-4-ol has been used as a model sulfur-containing compound in a study of molecular metal sulfide cluster substrate binding to oil-refinery hydrodesulfurization catalysts <2002IC1336> and also as a model compound in an evaluation of the removal of heterocyclic S-containing compounds from oil precursors by supercritical water <1995MI1485>. 

Catalysts were some of the first nanostructured materials applied in industry, and many of the most important catalysts used today are nanomaterials. These are usually dispersed on the surfaces of supports (carriers), which are often nearly inert platforms for the catalytically active structures. These structures include metal complexes as well as clusters, particles, or layers of metal, metal oxide, or metal sulfide. The solid supports usually incorporate nanopores and a large number of catalytic nanoparticles per unit volume on a high-area internal surface (typically hundreds of square meters per cubic centimeter). A benefit of the high dispersion of a catalyst is that it is used effectively, because a large part of it is at a surface and accessible to reactants. There are other potential benefits of high dispersion as well— nanostructured catalysts have properties different from those of the bulk material, possibly including unique catalytic activities and selectivities. 

A metal sulfide cluster Cp2Mo2Co2(CO)4 S3 (6), potentially having some structural features of a sulfided Co-Mo/AI2O3 catalyst surface, reacts with thiophene at 150°C under 15 atm of H2 (equation 18) to give an essentially quantitative yield of the cubane cluster Cp2Mo2Co2(CO)2S4 (7). The thiophene sulfur is incorporated into the cluster, and the hydrocarbon portion is converted to a mixture of Ci-4 alkanes and alkenes. The mechanism of this reaction may involve initial S-coordination of thiophene to (6). 

A comprehensive study of periodic trends in the electronic structures of transition-metal sulfides using MS-SCF-Aa calculations was undertaken by Harris (1982) and Harris and Chianelli (1984). This study employed clusters (see Chapter 6) and led to a suggestion that the... 

Harris, S. (1982). Study of the electronic structure of first and second row transition metal sulfides using SCF-SW-Aoi cluster calculations. Chem. Phys. 67, 229-37. 

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