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), [OSSO]­NbCl3 (7), and [OSSO]­TaCl3 (8), where the metal centers adopted cis-α configurations of the [OSSO] tetradentate ligand. The tantalum­(V) complex 8 with iBu3Al/(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%, Mw = 9100 g mol–1, PDI = 1.6); this is the first group 5 metal catalyst for α-olefin polymerization to afford a highly isospecific polymer.