Molybdenum sulfur derivatives

Table 5 shows HDS product distributions over several catalysts prepared by using the molybdenum-nickel cluster 2. Sulfur content in decane was adjusted to 5.0 wt% in these experiments. MoNi/NaY was found to be more active than MoNi/Al203. It is to be noted that during the high temperature pretreatment the original cluster structure would have been changed. However, the high activity of the MoNi/NaY catalyst for benzothiophene HDS is probably due to the formation of active sites derived from this particular mixed metal cluster. 

The formation of rings that contain a thioether linkage does not appear to be catalyzed efficiently by Ru, even when terminal olefins are present. On the other hand, molybdenum appears to work relatively well, as shown in Eqs. 30 [207] and 31 [208]. Under some conditions polymerization (ADMET) to give poly-thioethers is a possible alternative [26]. Aryloxide tungsten catalysts have also been employed successfully to prepare thioether derivatives [107,166,169]. Apparently the mismatch between a hard earlier metal center and a soft sulfur donor is what allows thioethers to be tolerated by molybdenum and tungsten. Similar arguments could be used to explain why cyclometalated aryloxycarbene complexes of tungsten have been successfully employed to prepare a variety of cyclic olefins such as the phosphine shown in Eq. 32 [107,193]. 

The first research group to propose a description of the structure of CoMo catalysts was led by Schuit and Gates (13). This group introduced the so-called monolayer model directly derived from the physical studies of CoMo oxide precursors supported on y-alumina carried out by J. T. Richardson (14) (Richardson first proposed the existence of a special Co/Mo entity.) In this model the upper or first layer contained only sulfur atoms, each bonded to a molybdenum atom of the second layer (below the first one), these molybdenum atoms being bonded to two oxygen atoms also located in this second layer. When a sulfur atom was removed by reduction (H2 flow) of Mo5+ to Mo3+, a vacancy was formed at the surface and became the preferential adsorption site of a sulfur atom in the organic gas phase. The presence of cobalt incorporated into underlying layers of the alumina... 

Amine salts have been used to recover molybdenum from solutions arising from a variety of sources. Most of the western world s supply of this metal is derived from molybdenite (MoS2) concentrates obtained as a byproduct of copper production in the USA and Chile. Such concentrates are roasted to molybdenum(VI) oxide (volatile Re207 can often be recovered as a valuable byproduct from the roaster gases) and leached with dilute sulfuric acid to remove the copper from the crude M0O3 product. Some molybdenum also dissolves and can be recovered, for example, by the same technique as that practised at Kennecott s Utah Copper Division smelter,213 i.e. by extraction into a solution of a tertiary amine in kerosene at an aqueous pH value of about 1. 

A cofactor can be extracted from the iron-molybdenum protein, using Af-methylformamide. This cofactor (called FeMoCo) has many spectroscopic properties in common with the native protein, especially the EXAFS spectrum, and activates the inactive large protein derived from Azobacter vinelandii UW45 mutant which cannot incorporate molybdenum. The cofactor contains no protein or peptide, but does contain molybdenum, iron, and sulfur in atomic ratios of 1 6-8 4-9. It is believed to contain the dinitrogen-binding site (presumably molybdenum) but there is no definitive proof of this. 

Displacement of trimethylphosphite from (CpMo(MeC=CR)[P-(OMe)3]2 + with anionic sulfur nucleophiles produces neutral monoalkyne molybdenum derivatives [Eq. (22)] (74). Methoxide has also been incorporated into monoalkyne cyclopentadienyl derivatives [Eq. (23)] (75). 

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