Synthesis, Structure, and 1-Hexene Polymerization Catalytic Ability of Group 5 Metal Complexes Incorporating an [OSSO]-Type Ligand

Group 5 metal complexes bearing an [OSSO]-type bis(phenolate) ligand have been successfully prepared by the reaction of a bis(phenol) compound 3 or its dilithio salt 6 with VO(OPr)(3), NbCl5, or TaCl5. X-ray crystallographic analyses revealed the monomeric nature of the resulting complexes, [OSSO]VO(OPr) (5), [0550]NbCl3 (7), and [OSSO]TaCl3 (8), where the metal centers adopted cis-alpha configurations of the [OSSO] tetradentate ligand. The tantalum(V) complex 8 with (Bu3Al)-Bu-i/(Ph3C)[B(C6F5)(4)]as an activator catalyzed the polymerization of 1-hexene to provide completely isotactic poly(1-hexene), with a narrow molecular weight distribution ([mmmm] > 95%, M-w, = 9100 g mol(-1), PDI = 1.6); this is the first group 5 metal catalyst for a-olefin polymerization to afford a highly isospecific polymer.