New complexes of aluminum and titanium containing sterically demanding ligands and their reaction with B(C₆F₅)₃ are reported. Treatment of [(Ph₂MeSiCH₂CH₂)₃Si]NCN[Si(CH₂CH₂SiMePh₂)₃] (1) or Si(CH₂CH₂SiMePh₂)₃OH (2) with 1 equiv of AlMe₃ results in the formation of the neutral dimethylaluminum complexes {MeC[NSi(CH₂CH₂SiMePh₂)₃]₂}AlMe₂ (3) and [(Ph₂MeSiCH₂CH₂)₃SiOAlMe₂]₂ (4). Reaction of 3 with 1 equiv of B(C₆F₅)₃ forms the neutral complex {MeC[NSi(CH₂CH₂SiMePh₂)₃]₂}AlMe(C₆F₅) (5) and BMe(C₆F₅)₂. In the case of 4, the analogous reaction produced the dimer [(Ph₂MeSiCH₂CH₂)₃SiOAl]₂Me₃(C₆F₅) (6). Treatment of 1 with Ti(C₅Me₅)Me₃ fails to afford the corresponding amidinate complex. However, reaction of 2 with the same titanium half-sandwich complex cleanly gives Ti(C₅Me₅)[OSi(CH₂CH₂SiMePh₂)₃]Me₂ (7). Reaction of 7 with 1 equiv of B(C₆F₅)₃ leads to the formation of the ion pair {Ti(C₅Me₅)[OSi(CH₂CH₂SiMePh₂)₃]Me}[BMe(C₆F₅)₃] (8), which is relatively stable at room temperature, slowly decomposing (t_1/2 ≈ 48 h) to give a mixture of two neutral titanium complexes, Ti(C₅Me₅)[OSi(CH₂CH₂SiMePh₂)₃][CH₂B(C₆F₅)₂](C₆F₅) (9) and Ti(C₅Me₅)[OSi(CH₂CH₂SiMePh₂)₃]Me(C₆F₅) (10). However, when this reaction is carried out in a 1:0.5 stoichiometry, the decomposition process occurs over the course of 22 h, giving complex 10 selectively. The implications of these results with related Ziegler−Natta catalyst systems are discussed.

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National Institute of Health (NIHR) Biomedical Research Centres (BRC)

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