Tungsten complexes structures

Group 4, surface chemistry on oxides, 12, 515 Group 5, surface chemistry on oxides, 12, 524 molybdenum, surface chemistry on oxides, 12, 529 into nickel complexes, 8, 59-60 with palladium, GO insertion, 8, 200 tungsten, surface chemistry on oxides, 12, 531 on zinc compounds, 2, 366 Alkoxido-imido tungsten complexes structure and properties, 5, 754—755 synthesis, 5, 750/... 

Phosphine-imido tungsten complexes structure and properties, 5, 754—755 synthesis, 5, 749... 

Very recently, synthesis and structure of molybdenum and tungsten complexes of the relatively unhindered disilene Si2Me4 were reported. The x-ray structure of 84 shows a metallacyclosilane structure with W — Si = 2.606(2) A and Si —Si = 2.260(3) A. The W — Si bond length is within the range of various estimates of the Si and W covalent radii and the Si —Si distance falls midway between the expected values for a single (2.35 A) and a double bond (2.14 A) (Fig. 13). 

The potential of Fischer carbene complexes in the construction of complex structures from simple starting materials is nicely reflected in the next example. Thus, the reaction of alkenylcarbene complexes of chromium and tungsten with cyclopentanone and cyclohexanone enamines allows the di-astereo- and enantioselective synthesis of functionalised bicyclo[3.2.1]octane and bicyclo[3.3.1]nonane derivatives [12] (Scheme 44). The mechanism of this transformation is initiated by a 1,4-addition of the C -enamine to the alkenylcarbene complex. Further 1,2-addition of the of the newly formed enamine to the carbene carbon leads to a metalate intermediate which can... 

Fig. 3 X-ray crystal structures of the radical tungsten complexes in [Me2C(r 5-C5H4)2W(dmit)]+" and [(r -C5H4But)2W(dmit)]+"...

Probably the first isolated tungsten alkylidene complex active in metathesis and completely characterised is the one shown in Figure 16.10 reported by Wengrovius and Schrock the analysis included an X-ray structure determination by Churchill and co-workers [18], The alkylidene was transferred from a tantalum complex to yield the hexacoordinate tungsten complex containing two PEt3 ligands. One of these can be removed by the addition of half an equivalent of palladium chloride. The total turnover number of these catalysts with Lewis acids added was 50 in 24 hours. 

It is also worthy to note that the pentacarbonyl-tungsten complex of the phosphirenylium cation (5) has been recently reported, but no X-ray structure has been obtained. B3LYP/6-311G(d) optimization of the presumed -Cr(CO)5 complex of 5 resulted in an 7 -form (Figure 1) when starting from the bound chromium complex. Such a structure is in complete accord with a delocalized electronic structure of the cation. 

Catalytic activities of [Ru PW (H30)(0)3, ] -/03/CH3CN/80°C and of [Ru PMOjj(H30)(0)3, ] "/03/CH3CN were compared. The tungsten complex did not catalyse the aerobic oxidation of cumene and 1-octene to cumyl alcohol and 1-octene oxide while the Mo analogue did so the tungsten complex underwent structural change with to an inert form, while its molybdenum analogue did not... 

Further confirmation of the structure comes from the X-ray crystal structure analysis of the cyclopropylcarbinyl tungsten complex CpW(CO)3(C5FI9) which reveals a tetragonal bipyramidal geometry at the metal, and a typical bisected conformation of the cyclo-propylcarbinyl-M moiety. The sigma C—M bond distance of 234 pm is expectedly much longer than the W—CO bonds (115 pm). 

Tungsten, hexahydridotris(diisopropyiphenylphosphine)-structure, 700 Tungsten alkoxides physical properties, 346 synthesis, 339 Tungsten complexes alkoxy carbonyl reactions, 355 alkyl alkoxy reactions, 358 amides... 

Fig. 10. Molecular structure of the zirconoxycarbene tungsten complex 104 obtained by diastereoselective alkylation of 103.

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