A method for the synthesis of a homogeneous cationic tungsten(VI)pentamethyl complex [(WMe5)+(C6F5)3BMe−] from neutral tungstenhexamethyl (WMe6) and a silica supported cationic tungstentetramethyl complex [(Si–O–)WMe4+ (C6F5)3BMe−] from a neutral silica supported tungstenpentamethyl complex [(Si–O–)WMe5] is described. In both cases a direct demethylation using the B(C6F5)3 reagent was used. The aforesaid complexes were characterized by liquid or solid state NMR spectroscopy. Interestingly, the homogeneous cationic complex [(WMe5)+(C6F5)3BMe−] shows moderate activity whereas the supported cationic complex [(Si–O–)WMe4+(C6F5)3BMe−] exhibits good activity in olefin metathesis reactions.