Iron clusters carbon monoxide

Iron Sulfur Compounds. Many molecular compounds (18—20) are known in which iron is tetrahedraHy coordinated by a combination of thiolate and sulfide donors. Of the 10 or more stmcturaHy characterized classes of Fe—S compounds, the four shown in Figure 1 are known to occur in proteins. The mononuclear iron site REPLACE occurs in the one-iron bacterial electron-transfer protein mbredoxin. The [2Fe—2S] (10) and [4Fe—4S] (12) cubane stmctures are found in the 2-, 4-, and 8-iron ferredoxins, which are also electron-transfer proteins. The [3Fe—4S] voided cubane stmcture (11) has been found in some ferredoxins and in the inactive form of aconitase, the enzyme which catalyzes the stereospecific hydration—rehydration of citrate to isocitrate in the Krebs cycle. In addition, enzymes are known that contain either other types of iron sulfur clusters or iron sulfur clusters that include other metals. Examples include nitrogenase, which reduces N2 to NH at a MoFe Sg homocitrate cluster carbon monoxide dehydrogenase, which assembles acetyl-coenzyme A (acetyl-CoA) at a FeNiS site and hydrogenases, which catalyze the reversible reduction of protons to hydrogen gas. 

The acetogenic bacterium Moorella thermoacetica contains a cofactor comprising iron, sulfur, copper and nickel in the enzyme carbon monoxide dehyd-rogenase/acetyl-CoA, and Drennan et al. proposed a new role for Cu in biology on the basis of their structure determination at 2.2 A resolution.81 The Cu bridges the Fe4S4 cluster and Ni centre via three p2-S atoms, and hence the reported EPR... 

The methods described here are based on the thermal stability of such clusters under CO pressure.4 In the case of Co2Fe(CO)9S, the complex itself is stable under hydroformylation conditions (130-180 °C, 50-150 bar CO and H2) and is formed under such conditions from almost every sulfur-containing substance, iron, cobalt, and carbon monoxide.1 Ethanethiol is used in the procedure as the sulfur source because of its reactivity. The dihydride cluster Fe3H2(CO)9S is not directly accessible by this method because it is a thermally much less stable species but the anion Fe3H(CO)9S" can be prepared in this way and its acidification yields the desired complex. 

Both hydrogenases and carbon monoxide oxidoreductases contain iron-sulfur clusters in addition to nickel. It may be noted that in addition to the Ni hydrogenases, there is another class of Fe hydrogenases, such as those in clostridia, which contain no nickel but have a specialized type of iron-sulfur cluster (28a, 28b). Therefore, it has to be established that the nickel in Ni hydrogenases is the active site as will be seen later, there is a considerable amount of circumstantial evidence for this. 

Heme coenzymes, iron-sulfur clusters, flavin coenzymes, and nicotinamide coenzymes cooperate in multienzyme systems to catalyze the chemically remarkable hy-droxylations of hydrocarbons such as steroids (chapter 20). In these hydroxylation systems, the heme proteins constitute a family of proteins known as cytochrome P450, named for the wavelength corresponding to the most intense absorption band of the carbon monoxide-liganded heme, an inhib-... 

A mechanism for the oxidation of carbon monoxide at cluster C has been proposed [139] in it CO and water bind to the cluster (Figure 6a). By analogy with cyanide binding, water is proposed to bind to the high-spin Ni(II) and CO to an iron atom of the cluster. After dehydronation of the water molecule the resulting hydroxide attacks the CO to form -COOH. Dehydronation of this spe-... 

The compound K2 [Rh6(CO)15C] is a yellow powder. It is sensitive to air both in the solid state and in solution and is quite soluble in water, methanol, ethanol, acetone, THF, and acetonitrile. The salts of other cations can be obtained by metathesis, in water for the cesium salt and in methanol for the larger tetra-alkylammonium or phosphonium cations. The tetraethylammonium salt is sparingly soluble in THF, whereas the benzyltrimethylammonium and bis-(triphenylphosphine)imminium salts are soluble. All of these salts are soluble in acetone and acetonitrile. The yellow solution of the potassium salt in THF shows characteristic IR bands at 2040 (vw), 1990 (vs), 1885 (vw), 1845 (s), 1830 (sh, m) 1815 (sh, br) and 1775 (vw, br) cm-1. The IR spectral band shapes depend on solvents and cations. The oxidation of K2 [Rh6(CO)i5C] with iron-(III) ammonium sulfate in water under carbon monoxide leads to the octa-nuclear carbido carbonyl cluster Rhg(CO)i9C,6 whereas under nitrogen RhntCO sQ7 or [H30] [Rhls(CO)28C2]8 is obtained. 

As discussed in Section IIIC, it has been suggested that the nickel site in carbon monoxide dehydrogenases is associated with an iron-sulfur cluster 266). Possible geometries include a mixed-metal cubane, [Ni-3Fe-4S] and a sulfur-bridged assembly (Fig. 60). A synthetic [Ni-3Fe-4S] cluster has been characterized and its Mossbauer properties are very similar to those of CODH from C. thermoaceticum 86). 

CF3H, Methane, trifluoro-cadmium complex, 24 55 mercury complex, 24 52 CF3NOS, Imidosulfurous difluoride, (fluorocarbonyl)-, 24 10 CH2, Methylene ruthenium complex, 25 182 CH2CI4P2, Phosphine, methylenebis-(dichloro)-, 25 121 CH3, Methyl cobalt complexes, 23 170 mercury complexes, 24 143-145 platinum complex, 25 104, lOS CNO, Cyanato silicon complex, 24 99 CN2OS2, l,3k, 2,4-Dithiadiazol-5-one, 25 53 CO, Carbon monoxide chromium complexes, 21 1, 2 23 87 cobalt complex, 25 177 cobalt, iron, osmium, and ruthenium complexes, 21 58-65 cobalt-osmium complexes 25 195-197 cobalt-ruthenium cluster complexes, 25 164... 

OC, Carbon monoxide chromium complex, 21 1, 2 chromium and tungsten complexes, 23 27 cobalt complex, 25 177 cobalt complexes, 23 15-17, 23-25 cobalt, iron, osmium, and ruthenium complexes, 21 58-65 cobalt-osmium complexes, 25 195-197 cobalt-ruthenium cluster complexes, 25 164... 

K. Lazar, Z. Schay and L. Guezi, Direct evidence for the conelation between surface carbon and carbon monoxide + hydrogen selectivity on iron and iion-mtbenium catalysts prepared form metal carbonyl clusters, 1. Mol. Catal. 17(2-3) (1982) 205-218. 

Transition metal catalysts, specifically those composed of iron nanoparticles, are widely employed in industrial chemical production and pollution abatement applications [67], Iron also plays a cracial role in many important biological processes. Iron oxides are economical alternatives to more costly catalysts and show activity for the oxidation of methane [68], conversion of carbon monoxide to carbon dioxide [58], and the transformation of various hydrocarbons [69,70]. In addition, iron oxides have good catalytic lifetimes and are resistant to high concentrations of moisture and CO which often poison other catalysts [71]. Li et al. have observed that nanosized iron oxides are highly active for CO oxidation at low tanperatures [58]. Iron is unique and more active than other catalyst and support materials because it is easily reduced and provides a large number of potential active sites because of its highly disordered and defect rich structure [72, 73]. Previous gas-phase smdies of cationic iron clusters have included determination of the thermochemistry and bond energies of iron cluster oxides and iron carbonyl complexes by Armentrout and co-workers [74, 75], and a classification of the dissociation patterns of small iron oxide cluster cations by Schwarz et al. [76]. 

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