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Neutral and Cationic Aluminum and Titanium Complexes Incorporating Sterically Demanding Organosilicon Ligands

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posted on 09.05.2005, 00:00 by Virginia Amo, Román Andrés, Ernesto de Jesús, F. Javier de la Mata, Juan C. Flores, Rafael Gómez, M. Pilar Gómez-Sal, John F. C. Turner
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 (t1/2 ≈ 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.