Halide Effects in the Formation of Four-Coordinate, Cationic Aluminum

This work was conducted as part of a broad-based effort to determine the factors that affect cation formation for organometallic aluminum complexes. In this study the adduct species R₂AlX·NH₂^tBu (R, X: Me, F (1); Me, Cl (2); Et, Cl (3); Me, Br (4)) and cationic complexes [R₂Al(NH₂^tBu)₂]X (R, X: Me, Br (5); Et, Br (6); Me, I (7)) were examined. These complexes demonstrate that the reaction of R₂AlX with excess NH₂^tBu produces cationic complexes only when X = Br or I. All of the compounds were characterized by melting points, ¹H NMR, IR, elemental analyses, and, in some cases, X-ray crystallography. X-ray data: 2, triclinic, P1, a = 6.277(3) Å, b = 8.990(3) Å, c = 10.393(3) Å, a = 71.97(1)°, β= 80.25(3)°, γ = 81.97(3)°, V = 547.0(4) ų, Z = 2, 1032 reflections with F > 4.0 σ(F), R = 0.0520; 5, monoclinic, P2_1/c, a = 9.099(1) Å, b = 10.292(1) Å c = 17.255-(2) Å, β= 104.81(1)°, V = 1562.1(3) ų, Z = 4, 1464 reflections with F > 4.0 σF, R = 0.0387; 6, monoclinic, P2_1/c, a = 14.122(2) Å, b = 13.539(2) Å, c = 21.089(2) Å, β= 107.73(1)°, V = 3841.2(9) ų, Z = 4, 781 reflections with F > 5.0 σF, R = 0.0873; 7, monoclinic, P2_1/n, a = 9.071(1) Å, b = 10.529(1) Å, c = 17.714(2) Å, β = 103.67(1)°, V = 1644.0(3) Å₃, Z = 4, 1723 reflections with F > 4.0 σF, R = 0.0451.