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(SiMe3)C(R-1)C(R-2)(C5H4N-2)}](2) (1a, 2a, and 3a) were each treated with MCl4 to afford the racemic complexes [M{N(SiMe3)C(R-1)C(R-2)(C5H4N-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 = SiMe3 (3b)). Similarly, Li{N(SiMe3)C(Ph)C(R)(C9H6N-2)} (4a and 5a) afforded the racemic complexes [Zr{N(SiMe3)C(Ph)C(R)(C9H6N-2)}(2)Cl-2] (R = H (4b); R = SiMe3 (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-C5H4N]) demonstrate that (i) the frontier orbitals are similar to those of [Zr(eta(5)-C5H5)(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 ZrCl4 with [Zr{N(SiMe3)C(R-1)C(R-2)(C5H4N-2)}(2)Cl-2] or [Zr{N(SiMe3)C(Ph)C(SiMe3)(C9H6N-2)}(2)Cl-2] afforded the mono(1-azaallyl)zirconium complexes Zr{N(SiMe3)C(R-1)C(R-2)(C5H4N-2)}Cl-3 (R-1 = Bu-t, R-2 = H (2d); R-1 = Ph, R-2 = SiMe3 (3d)) and Zr{N(SiMe3)C(Ph)C(SiMe3)(C9H6N-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.