Aminotroponiminato Hafnium and Zirconium Complexes: Synthesis and Ethylene/1-Octene Copolymerization Study

Four new aminotroponiminato hafnium and zirconium tribenzyl complexes were prepared by reacting neutral ligands with the corresponding tetrabenzyl complexes. Aminotroponimine ligands were prepared in four steps starting from tropolone. An air-stable ethoxy-amino-tropylium cation intermediate isolated during ligand synthesis was found to react directly with amines significantly faster than the neutral intermediate proposed previously. This tropylium cation represents a convenient way to prepare a large array of aminotroponimines. An ethylene/1-octene copolymerization study conducted at 120 °C demonstrated that the aminotroponiminato hafnium and zirconium complexes are catalytically active, but their activity is lower than that observed for the corresponding imino–enamido complexes. Polymer analysis data (GPC and DSC) indicated that aminotroponiminato complexes generate at least two catalytically active species under polymerization conditions.