Zirconium(IV) complexes having a rigid 1,8-naphthalene diamide versus a flexible 1,3-propylene diamide for olefin polymerization

Structure and chemical properties of zirconium(IV) complexes containing a rigid naphthalene diamide ligand ([1,8-C10H6(NSiMe3)(2)](2-)) or flexible propylene diamide ligands ([1,3-C3H6(NR)(2)](2-), R = SiMe3, Si(i-Pr)(3)) are described. The reaction of 1,8-C10H6(NHSiMe3)(2) with Zr(NMe2)(4) in refluxing toluene yields [1,8-C10H6(NSiMe3)(2)]Zr(NMe2)(2) (1), and the product 1 is converted to [1,8-C10H6(NSiMe3)(2)]ZrCl2 (2) in a moderate isolation yield by the treatment with excess ClSiMe3. X-ray crystallographic analysis establishes that 2 forms a dimer associated through two chloride bridges in the solid state and has a highly puckered six-membered ring with a small N-Zr-N bite angle (91.05 degrees). The reaction of 1,3-C3H6(NHR)(2) (R = SiMe3, Si(i-Pr)(3)) with Zr(NMe2)(4) also affords [1,3-C3H6(NR)(2)]Zr(NMe2)(2). Treatment of the amide complex with excess ClSiMe3 results in [1,3-C3H6(NR)(2)]ZrCl2 (4, R = SiMe3; 5, R Si(i-Pr)(3)) in a facile manner. The crystal structure of 5 shows that the molecule is monomeric, featuring a mirror plane that passes the zirconium atom and two chloride atoms, and the chelate and the metal form a boatlike six-membered ring with a large N-Zr-N angle (104.31 degrees). While these zirconium(IV) diamide complexes (2, 4, and 5) exhibit moderate ethylene polymerization activity (10-90 kg of PE/(mol(cat).atm.h)) in the presence of methylalumoxane, the diamide dimethyl compound [1,3-C3C6(NSi(i-Pr)(3))(2)]ZrMe2 (6) shows a high activity (300 kg of PE/(mol(cat).atm.h)) for the ethylene polymerization when it is activated with Ph3CB(C6F5)(4).