Organoaluminum-Thiacrown Ether Chemistry. Synthesis and Molecular Structure of [Al(CH3)3]4[12]aneS4: An Unusual Example of an Endodentate Conformation of [12]aneS4

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Abstract
The crystalline organoaluminum macrocyclic ligand complex [Al(CH3)3]4[12]aneS4 was prepared by reaction of the sulfur-based crown ether_ with trimethylaluminum in toluene. The title compound crystallizes in the triclinic space group P1 with unit cell parameters a α 8.548(2), b α 9.949(3), c α 11.225(3)Å, α α 64.08(2), β α 78.55(2), γ α 86.96(3)[ddot], V α 840Å3, and D c α 1.04gcm-3 for Z α 1. Least-squares refinement based on 1761 observed reflections (I ≥ 3[sgrave](I)) in the range 3.50[ddot] < 20 < 45.0[ddot] converged at R α 0.034, R w α 0.044. The molecule is situated about a crystallographic centre of symmetry with the four sulfur atoms constituting a plane. As evidenced by the independent distances of 2.530(1) Å and 2.500(1) Å, the A1-S interactions in the organoaluminum complex are rather substantial. Particularly significant is the fact that the conformation of the macrocycle in the title compound is endodentate as the four sulfur atoms are directed towards the interior of the macrocyclic cavity even as it accommodates four trimethylaluminum units.