Base Effects on the Formation of Four- and Five-Coordinate Cationic Aluminum Complexes

This work was conducted as part of our continuing effort to determine the factors that affect cation formation for organometallic aluminum complexes. In this study, the interactions of R₂AlX (where R = Me, ⁱBu, ^tBu; X = Cl, Br, I) with the monodentate bases thf, pyridine, NEt₃, HNⁱPr₂, H₂NⁱBu, H₂N^tBu, and O=PPh₃ are examined to determine the role of the base in cation formation. These reactions resulted in the neutral adducts of the general form R₂AlX-base (1-6, 8, 10, and 12) as well as the cationic complexes [R₂Al(base)₂]X (7, 9, and 11). The reactions of Me₂AlX (where X = Cl, Br) with PMDETA (N,N′,N″,N‴-pentamethyldiethylenetriamine) and the catalytic activity of the resulting cationic complexes (13 and 14) are also discussed. All of the compounds were characterized by mp, IR, ¹H-NMR, and elemental analyses, and in one an X-ray crystallographic study was carried out. X-ray data for 13: triclinic, P1̄, a = 6.9542(6) Å, b = 12.2058(10) Å, c = 13.2417(11) Å, α = 106.236(2)°, β = 98.885(2)°, γ = 93.807(2)°, V = 1059.06(15) ų, and Z = 2 for 181 parameters refined on 4358 reflections having F > 6.0σ(F), R = 0.0697, and R_w = 0.0697.