Unexpected Conformation of the Hydrogen Chloride Salt of [14]aneN4: An X-ray Structural Examination of [H2[14]aneN4H2]C14 and its Role in Organoaluminum Host-Guest Chemistry

Abstract
The macrocyclic salt [H2[14]aneN4H2]Cl4 was prepared and its X-ray crystal structure was determined. The salt crystallizes in the orthorhombic space group Pnna with unit cell parameters a α 14.257(11), b α 7.796(5), c α 17.785(9) Å3, V = 1976.8(2) Å3, and D c α 1.28gcm-3 for Z α 4. Least-squares refinement based on 1086 observed reflections (I > 3[sgrave](I)) converged at R α 0.055 (R w α 0.075). The macrocyclic cation is in an unusual exodentate conformation. Additionally, the X-ray crystal structure of the uncomplexed macrocyclic tetradentate secondary amine [14]aneN4 was determined. The neutral macro-cycle crystallizes in the triclinic space group P1 with unit cell parameters a α 4.698(3), b α 8.683(5), c α 15.388(12) Å, α α 90.63(6), β α 97.38(6), γ α 98.99(5)[ddot], V α 614.6(8) Å3, and D c α 1.08 gem-3 for Z α 2. Least-squares refinement based on 1458 observed reflections (I >3[sgrave](I)) converged at R α 0.086 (R w α 0.116). The endodentate conformation of the neutral macrocycle is stabilized by intramolecular hydrogen bonding by two aza-hydrogen atoms to the remaining two nitrogen atoms. The macrocyclic salt was shown to interact with trimethylaluminum resulting in an organoaluminum host-guest compound capable of accommodating 9.7 toluene molecules per anionic site.