Tungsten ligand exchange

Since most of the >/2-cyclopropenyl complexes are obtained by ligand exchange reactions (cf Section IV.B.l.a) it is reasonable to believe that the reactions of cyclopropenes with octahedral complexes of tungsten (equation 222)287 and rhuthenium (equation 223)294, which lead directly to vinyl alkylidenes complexes, pass through an unstable >/2-cyclo-... 

As discussed above, enthalpies of binding of H2 and N2 to (P(C6Hu)3)2W(CO)3 were determined by solution calorimetry. It was not practical to measure equilibrium constants for the tungsten complex since binding of both H2 and N2 is near quantitive under normal conditions. Using N2/H2 mixtures we have measured (2) the thermodynamic parameters for the ligand exchange reaction shown below ... 

Further experiments have dealt with the generation of more stable tungsten silanols via ligand exchange at the metal and the reactivity of the iron-substituted silanol 5 in controlled condensation reactions. 

The ligand exchange reactions with molybdenum and tungsten hexacarbonyl compounds also proceed as shown in eq. (13.17). Reactions with phosphine are shown in eq. (13.18) [29]. 

Similar reactions proceed in the presence of molybdenum and tungsten complexes as catalysts. These catalysts are more reactive than chromium catalysts but the reaction selectivities are low. The induction period is usually one hour. The induction period is thought to be caused by the ligand exchange reaction of an aryl group and diene with the obvious formation of an intermediate as shown in eq. 

V. Solvent Exchange and Ligand Substitution on Some Molybdenum and Tungsten Cluster Complexes... 

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