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

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.