Tungsten derivatives

Mixed gold] III) and molybdenum or tungsten derivatives can be obtained by ligand displacement or bridge-cleavage reactions. Thus, treatment of [M]CO)4]tdppme)]... 

Essentially six resonance structures (G-L in Eig. 11) have to be taken into account for complexes 72, their spectroscopic data, as well as the X-ray structural analysis performed on the tungsten derivative, suggesting that strongly dipolar ylidic structures J-L are the most important contributions to the overall bonding situation. 

A similar hydride transfer was observed by Ipaktschi in the rearrangement of a 3-dialkylaminovinylidene-tungsten derivative [55]. 

Domingo, J.L. 2002. Vanadium and tungsten derivatives as antidiabetic agents A review of their toxic effects. Biol. Trace Elem. Res. 88 97-112. 

The metal carbene species can be formed in a similar way in systems with the WCl6-SnMe4 catalyst in which, however, the disproportionation of a methylated tungsten derivative takes place [104] ... 

Of the rather limited number of tetravalent molybdenum and tungsten derivatives known, wre shall mention here only molybdenum disulfide (M0S2), which occurs as the ore molybdenite and the octacyano complexes Mo(CN)i 4 and W(CN) 4 which, along with their pentavalent counterparts (p. 333), represent two of the very few examples of octa-covalency. 

Tungsten derivatives, both CpW(CO)(RC=CH)(R ) and CpW(CO)-(RC=CH)[C(0)R ], consistently exhibit 13-C signals between 185 and 200 ppm with single bond xJCh values of 190-205 Hz for alkyl derivatives and 205-215 Hz for acyl derivatives (69). Incorporation of methoxide in place of the alkyl or acyl ligand shifts the alkyne carbons slightly upheld to 169 and 176 ppm (75), presumably reflecting competition between alkyne... 

This particular thiocarbenoid complex and the analogous tungsten derivative are more conveniently synthesized by an initial reaction of [Cr(CO)5 C(CH3)(OCH3) ] or [W(CO)5 C(CH3)(OCH3) ] with benzene-thiolate ion at room temperature followed by acidification with hydrochloric acid. This synthetic route has also been used to prepare a series of pentacarbonyl[(l-phenylthio)ethylidene]tungsten(0) complexes substituted in the 4-position of the phenyl rings.4... 

With respect to the corresponding molybdenum complexes, the tungsten derivatives are slightly more difficult to oxidize. 

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