Tungsten -, trans

Fawcett, J. et al., J. Chem. Soc., Dalton Trans., 1980, 2294-2296 Trimethylsilyl azide reacts with excess tungsten hexafluoride in solvent to give the title compound, which explodes at 63 °C or if dried in dynamic vacuum. A deficiency of the hexafluoride gave a mixture (presumably containing poly-azides) which exploded at ambient temperature. 

The cationic tungsten dihydride [Cp(CO)2(PMe3)W(H)2]+ hydrogenates the C=0 bond of propionaldehyde within minutes at 22 °C, leading to the formation of cis and truns isomers of Cp(CO)3W(l IO"Pr) Oif (Eq. (28)) [42]. The cis isomer of the alcohol complex released the free alcohol faster than the trans isomer. A similar stoichiometric ionic hydrogenation of acetone was also observed using [Cp(CO)2(PMe3)W(H)2]+. 

In another study the kinetics and mechanism of an unprecedented T/2-vinyl isomerization of a highly fluorinated tungsten(II) metalla-cyclopropene complex was studied (92). Photolysis of a tungsten(II) tetrafluoroaryl metallacycle 1 and perfluoro-2-butyne results in the formation of the kinetic rf -vinyl complex 2 in which the fluoride is trans to the inserted acetylene and cis to both carbonyl ligands. Upon heating 2 is converted to the thermodynamic rf -vinyl complex 3 in which the fluoride ligand is now cis to the inserted alkyne and trans to one CO and cis to the second CO ligand as shown in Scheme 1. 

In contrast, evidence for the formation of cis and trans isomers is provided by H NMR studies of crude reaction mixtures in the molybdenum and tungsten... 

Cyclopentene yields mixtures of ROMP and double-bond polymerization with some Ti and V initiators. ROMP occurs exclusively with molybdenum and tungsten initiators, as well as Re, Nb, and Ta initiators. The relative amounts of cis and trans structures vary with the initiator and temperature [Dall Asta et al., 1962 Pampus and Lehnert, 1974]. Metallocene initiators polymerize cyclopentene through the double bond, but the polymer structure consists of cis 1,3-placement (Coates, 2000 Kaminsky, 2001 Kelly et al., 1997]. 

N,05WCii)H(h, Tungsten, tetracarbonyl[(di-ethylamino)methylidyne](isocyanato)-trans-, 26 42... 

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