Tungsten (IV) carbenes for the metathesis of olefins. Direct observation and identification of the chain carrying carbene complexes in a highly active catalyst system

On addition of aluminium halides to the carbene complexes W(CHBut)(OCH2But)2X2 conversion into highly active catalysts for olefin metathesis occurs; the nature of the initiating and propagating species in olefin metathesis has been identified by n.m.r. spectroscopy.