Synthesis and characterization of a homogeneous and silica supported homoleptic cationic tungsten(<scp>vi</scp>) methyl complex: application in olefin metathesis

Abstract

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 [([triple bond, length as m-dash]Si-O-)WMe₄⁺ (C₆F₅)₃BMe^-] from a neutral silica supported tungstenpentamethyl complex [([triple bond, length as m-dash]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 [([triple bond, length as m-dash]Si-O-)WMe₄⁺(C₆F₅)₃BMe^-] exhibits good activity in olefin metathesis reactions.