Experimental Evidence for Large Ring Metallacycle Intermediates in Polyethylene Chain Growth Using Homogeneous Chromium Catalysts

摘要

Chromium catalysts play a central role in the oligomerization and polymerization of ethylene,as well as in the selective trimerization2 and,more recently,tetramerization3 of ethylene.While there has been a vigorous ongoing debate over the propagation mechanism in heterogeneous polymerization systems,strong experimental evidence has been obtained for the intermediacy of metallacycles in the selective trimerization of ethylene to l-hexene.A similar metallacyclic pathway has also been proposed for homogeneous titanium catalysts,supported by computational studies.