Effect of Terminal Aryloxo Ligands in Ethylene Polymerization Using Titanatranes of the Type, [Ti(OAr){(O-2,4‑R2C6H2)‑6-CH2}3N]: Synthesis and Structural Analysis of the Heterobimetallic Complexes of Titanatranes with AlMe3

Effects of aryloxo terminal ligands and AlMe3 in ethylene polymerization using a series of Ti­(OAr)­[{(O-2,4-R2C6H2)-6-CH2}3N] [R = Me (1), tBu (2); Ar = 2,6-Me2C6H3 (a), 2,6-iPr2C6H3 (b), 2,6-Ph2C6H3 (c), 2,6-F2C6H3 (d), C6F5 (e)] (1a–1e, 2d,2e) in the presence of methylaluminoxane (MAO) have been explored. Reactions of 1b,1d,1e, which showed an increase in the activity upon addition of a small amount of AlMe3, with 1.0 equiv of AlMe3 afforded heterobimetallic Ti–Al complexes, TiMe­(O-2,6-iPr2C6H3)­[(O-2,4-Me2C6H2-6-CH2)­(μ2-O-2,4-Me2C6H2-6-CH2)­(Me2Al-μ2-O-2,4-Me2C6H2-6-CH2)­N] (3b) and [TiMe­{(O-2,4-Me2C6H2-6-CH2)2(μ2-O-2,4-Me2C6H2-6-CH2)­N}]­[Me2Al­(μ2-OAr)] [Ar = 2,6-F2C6H3 (3d), C6F5 (3e)], in moderate yields, and their structures were determined by X-ray crystallography. In contrast, the similar reaction of 1a (which showed a decrease in the activity upon addition of AlMe3) yielded [Al­(μ2-O-2,6-C6H3)­Me2]2 and TiMe­[{(O-2,4-Me2C6H2)-6-CH2}3N] as isolated forms: [Al­(μ2-OC6F5)­Me2]2 was isolated from the mixture in the reactions of 1c,2d,2e. The isolated heterobimetallic complexes (3b,3d,3e) exhibited high catalytic activities for ethylene polymerization in the presence of MAO, suggesting that these bimetallic species play a role in this catalysis.