Molecular heterogeneous metathesis catalysts: An attempted synthesis of surface-anchored alkylidenetungsten complexes

The reactivity of the two alkylidynetungsten complexes, [W(≡CCMe₃)(CH₂CMe₃)₃] and [W(≡CCMe₃)Cl₃(dme)] (dme = 1,2-dimethoxyethane), was determined with the surface of different inorganic oxides, such as silica, alumina, silica-alumina and niobia; their catalytic activity was tested for the metathesis of cis-pent-2-ene. The most efficient solids resulted from the interaction of these complexes with the surface of partially dehydroxylated niobia and silica-alumina. An attempt to identify the surface complexes on niobia (most active system) and silica (less active system) revealed the presence of a number of different anchored complexes, some of them bearing a neopentylidene ligand. The possible correlation between catalytic activity and some of the most probable surface entities is discussed.