New Titanium Complexes with Two β-Enaminoketonato Chelate Ligands:  Syntheses, Structures, and Olefin Polymerization Activities

New titanium complexes with two nonsymmetric bidentate β-enaminoketonato (N,O) ligands (4a−e), [(Ph)NC(R₂)C(H)C(R₁)O]₂TiCl₂, have been synthesized. X-ray crystal structure reveals that complex 4a has a C₂-symmetric conformation with a distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4a−e are active catalysts for ethylene polymerization at room temperature, producing high molecular weight polyethylenes bearing linear structures. The 4a,b/MMAO catalyst systems exhibit the characteristics of a quasi-living polymerization of ethylene, producing polyethylenes with narrow molecular weight distributions. Moreover, the 4a−d/MMAO catalyst systems are also capable of promoting the quasi-living copolymerization of ethylene with norbornene at room temperature, yielding high molecular weight alternating copolymers with narrow molecular weight distributions. The quasi-living nature of the catalysts allows the synthesis of new A−B polyethylene-block-poly(ethylene-co-norbornene) diblock copolymer.