Molybdenum formed with

In the first family, the metal is coordinated by one molecule of the pterin cofactor, while in the second, it is coordinated to two pterin molecules (both in the guanine dinucleotide form, with the two dinucleotides extending from the active site in opposite directions). Some enzymes also contain FejSj clusters (one or more), which do not seem to be directly linked to the Mo centers. The molybdenum hydroxylases invariably possess redox-active sites in addition to the molybdenum center and are found with two basic types of polypeptide architecture. The enzymes metabolizing quinoline-related compounds, and derivatives of nicotinic acid form a separate groups, in which each of the redox active centers are found in separate subunits. Those enzymes possessing flavin subunits are organized as a2jS2A2, with a pair of 2Fe-2S centers in the (3 subunit, the flavin in the (3 subunit, and the molybdenum in the y subunit. 

The formation of molybdenum complexes with diols (formed by olefin oxidation) was proved for the use of the molybdenum catalysts. Therefore, the participation of these complexes in the developed epoxidation reaction was assumed [242]. 

In the diagram shown in Figure 6.9, a sulfur atom has been inserted at the cluster s center in agreement with current thinking.24 The M center is attached to protein side chains at only two locations, cysteine 275 (at Fel) and histidine 442 (at Mo), and is unusual in having three-coordinate irons rather than the normal four-coordinate tetrahedral iron coordination sphere.29b The molybdenum forms... 

The metals sulfides are the most dangerous since after aerobic weathering they are transformed into water-soluble sulfates of different metals. Accordingly, in the areas of non-ferrous and rare metal ore exploration and treatments, the acid sulfate landscapes are formed with high content of toxic metals. The biogeochemical technogenic provinces are known, for instance, copper-nickel provinces in the Kola Peninsula, Fennoscandia molybdenum provinces in the Caucasian region, copper and chromium-nickel ones in the South Ural, poly-metal ones, in the Pacific coast of eastern Eurasia (Russia, China, and Korea), etc. 

Structures known to form with either metal also form with the entire intermediate range of mixed-metal combinations 180). Both molybdenum and tungsten form the heptametalate [M7O24]6 in aqueous solution. The existence of mixed heptametalates has been shown by the application of 170 NMR 182) and 183W NMR spectroscopy 180). In fact, molybdenum can replace any or all of the tungsten atoms in [W7O24]6 so that at least 19 mixed-metal structures can be observed 180). Approximate relative stability constants have been determined for the intermediate species in the series... 

Compound 388 is an acylating agent for electron-deficient alkenes, in a Michael addition process. It is formed by treating molybdenum hexacarbonyl with an organolithium compound, followed by quenching the intermediate 387 with boron trifluoride (equation 104). The structure of 388 (R = Ph) can be elucidated by NMR spectroscopy. Other examples of enantioselective and diastereoselective Michael-type additions involving lithium-containing intermediates in the presence of chiral additives can be found elsewhere in the literature . 

Molybdenum combines with fluorine gas at ordinary temperatures forming colorless hexafluoride, MoFe ... 

Finely divided molybdenum reacts with carbon monoxide under pressure to form molybdenum hexacarbonyl ... 

TBHP and the molybdenum catalysts are soluble in imidazohiun-based RTlLs. The system becomes biphasic when the olefinic substrate is added. In all cases, the TOFs of the catalytic reactions are considerably lower with the ionic solvent than when performed without the ionic solvent (data reported in Table 9). This slower catalytic reaction may be due to dilution effects and phase transfer problems, especially with the olefin, which is quite insoluble in the RTIL. The conversion appears to be strongly temperature-dependent, as decreasing the temperature from 55 °C to 35 °C reduces the conversion by ca. 50% (entries 7 and 8, Table 9). With the dioxomolybdenum complexes 1 and 2, the epoxidation reaction proceeds with 100% selectivity (Table 9), whereas some diol is formed with the catalyst 3. 

Complexes of molybdenum(IV) with 4-tolylimido ligands, (Ntol)2-, have been prepared by reduction of Mo3 1 and Mov species. Thus, [MoO(Ntol)(S2CNEt2)2] reacts with PPh3 to form... 

Zhiznevskii et al. chose another group of catalysts for the production of methacrolein, based on the solid solution systems Mo—Te oxides [110,360] and Sb—Te oxides [361] which were investigated in a pulse reactor at 340°C. Selectivities of 70—90% are reported. The Mo—Te catalyst (1 4) has a unique dependence of the activity upon the degree of reduction of the catalyst surface. Initial reduction to 6% increases activity, but further reduction lowered this again. The selectivity changes in a similar manner. X-Ray investigations led the authors to the conclusion that some Te—Mo—P-phase, which is formed with reduction but decomposed if the reduction is taken too far, is responsible. Combinations of Sb2Os and TeOz can likewise be selective catalysts. The relatively low activity at 400°C is much improved by the addition of molybdenum (60 mol.%). 

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