Novel Zirconium and Hafnium Complexes of Monoanionic Di-N,N‘-chelating Pyridyl- and Quinolyl-1-azaallyl Ligands and Their Activity in Olefin Polymerization Catalysis

The lithium complexes [Li{N(SiMe 3 )C(R 1 )C(R 2 )(C 5 H 4 N-2)}] 2 ( 1a, 2a, and 3a ) were each treated with MCl 4 to afford the racemic complexes [M{N(SiMe 3 )C(R 1 )C(R 2 )(C 5 H 4 N-2)} 2 Cl 2 ] (M = Zr, R 1 = Ph, R 2 = H ( 1b ); M = Zr, R 1 = Bu t, R 2 = H ( 2b ); M = Hf, R 1 = Bu t, R 2 = H ( 2c ); M = Zr, R 1 = Ph, R 2 = SiMe 3 ( 3b )). Similarly, Li{N(SiMe 3 )C(Ph)C(R)(C 9 H 6 N-2)} ( 4a and 5a ) afforded the racemic complexes [Zr{N(SiMe 3 )C(Ph)C(R)(C 9 H 6 N-2)} 2 Cl 2 ] (R = H ( 4b ); R = SiMe 3 ( 5b )). X-ray structural analysis of 2b, 2c, and 3b revealed that these complexes have C 2 octahedral geometries with their chloride ligands in cis positions. Molecular orbital calculations on model systems of the bis{3-(2-pyridyl)-1-azaallyl}zirconium system [Zr(LL) 2 ] 2+ (LL = [N(H)C(H)C(H)(2-C 5 H 4 N]) demonstrate that (i) the frontier orbitals are similar to those of [Zr(η 5 -C 5 H 5 ) 2 ] 2+ and (ii) the bis{3-(2-pyridyl)-1-azaallyl} ligand environment is more electron-donating, making the zirconium system less electrophilic. Conproportionation of ZrCl 4 with [Zr{N(SiMe 3 )C(R 1 )C(R 2 )(C 5 H 4 N-2)} 2 Cl 2 ] or [Zr{N(SiMe 3 )C(Ph)C(SiMe 3 )(C 9 H 6 N-2)} 2 Cl 2 ] afforded the mono(1-azaallyl)zirconium complexes Zr{N(SiMe 3 )C(R 1 )C(R 2 )(C 5 H 4 N-2)}Cl 3 (R 1 = Bu t, R 2 = H ( 2d ); R 1 = Ph, R 2 = SiMe 3 ( 3d )) and Zr{N(SiMe 3 )C(Ph)C(SiMe 3 )(C 9 H 6 N-2)}Cl 3 ( 5d ), respectively. When activated with methylaluminoxane (MAO), these compounds were highly active in ethylene polymerization. Compound 3d also showed modest activity in the polymerization of 1-hexene and the copolymerization of ethylene and 1-hexene.