Aminopyridinate–FI Hybrids,Their Hafnium and Titanium Complexes,and Their Application in the Living Polymerization of 1‐Hexene

Based on two well‐established ligand systems, the aminopyridinato (Ap) and the phenoxyimine (FI) ligand systems, new Ap‐FI hybrid ligands were developed. Four different Ap‐FI hybrid ligands were synthesized through a simple condensation reaction and fully characterized. The reaction of hafnium tetrabenzyl with all four Ap‐FI hybrid ligands exclusively led to mono(Ap‐FI) complexes of the type (Ap‐FI)HfBn₂]. The ligands acted as tetradentate dianionic chelates. Upon activation with tris(pentafluorophenyl)borane, the hafnium‐dibenzyl complexes led to highly active catalysts for the polymerization of 1‐hexene. Ultrahigh molecular weights and extremely narrow polydispersities support the living nature of this polymerization process. A possible deactivation product of the hafnium catalysts was characterized by single‐crystal X‐ray analysis and is discussed. The coordination modes of these new ligands were studied with the help of model titanium complexes. The reaction of titanium(IV) isopropoxide with ligand 1 led to a mono(Ap‐FI) complex, which showed the desired fac‐mer coordination mode. Titanium (IV) isopropoxide reacted with ligand 4 to give a complex of the type (ApH‐FI)₂Ti(OiPr)₂], which featured the ligand in its monoanionic form. The two titanium complexes were characterized by X‐ray crystal‐structure analysis.