Hetero-bimetallic Complexes of Titanatranes with Aluminum Alkyls: Synthesis, Structural Analysis, and Their Use in Catalysis for Ethylene Polymerization

Hetero-bimetallic Ti−Al complexes containing tris(aryloxo)amine ligands of type [TiR′{(μ₂-O-2,4-R₂C₆H₂-6-CH₂)(O-2,4-R₂C₆H₂-6-CH₂)₂N}][R′₂Al(μ₂-OⁱPr)] [3a,b and 4a; R = Me (3), ^tBu (4); R′ = Me (a), Et (b)] have been prepared by reacting Ti(OⁱPr)[(O-2,4-R₂C₆H₂-6-CH₂)₃N] [R = Me (1), ^tBu (2)] with 1.0 equiv of AlR′₃ in toluene. Crystallographic analyses of 3a,b and 4a reveal that these complexes have a distorted octahedral geometry around Ti and a distorted tetrahedral geometry around Al. Complexes 3a,b and 4a exhibited moderate catalytic activities for ethylene polymerization in toluene in the presence of methylaluminoxane (MAO) at 80−120 °C, and 4a showed higher activity than 3a,b. The tert-butyl analogue (4a) itself polymerizes ethylene without cocatalysts to afford high molecular weight polymer with a uniform distribution, clearly suggesting a hypothesis that cleavage of Ti−O bonds would generate the catalytically active cationic species in this catalysis.