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 R(2)AlX.NH(2)(t)Bu (R, X: Me, F (1); Me, Cl (2); Et, Cl (3); Me, Br (4)) and cationic complexes R(2)Al(NH(2)(t)Bu)(2)]X (R, X: Me, Br (5); Et, Br (6); Me, I (7)) were examined. These complexes demonstrate that the reaction of R(2)AlX with excess NH(2)(t)Bu produces cationic complexes only when X = Br or I. All of the compounds were characterized by melting points, (1)H NMR, IR, elemental analyses, and, in some cases, X-ray crystallography. X-ray data: 2, triclinic, P&onemacr;, a = 6.277(3) ?, b = 8.990(3) ?, c = 10.393(3) ?, alpha = 71.97(1) degrees, beta = 80.25(3) degrees, gamma = 81.97(3) degrees, V = 547.0(4) ?(3), Z = 2, 1032 reflections with F > 4.0 sigma(F), R = 0.0520; 5, monoclinic, P2(1)/c, a = 9.099(1) ?, b = 10.292(1) ?, c = 17.255(2) ?, beta = 104.81(1) degrees, V = 1562.1(3) ?(3), Z = 4, 1464 reflections with F > 4.0 sigmaF, R = 0.0387; 6, monoclinic, P2(1)/c, a = 14.122(2) ?, b = 13.539(2) ?, c = 21.089(2) ?, beta = 107.73(1) degrees, V = 3841.2(9) ?(3), Z = 4, 781 reflections with F > 5.0 sigmaF, R = 0.0873; 7, monoclinic, P2(1)/n, a = 9.071(1) ?, b = 10.529(1) ?, c = 17.714(2) ?, beta = 103.67(1) degrees, V = 1644.0(3) ?(3), Z = 4, 1723 reflections with F > 4.0 sigmaF, R = 0.0451.