The molecular structure of a complex of tetramethylcyclobutadiene and aluminium chloride,containing a σ-AlC bond

The molecular structure of the primary reaction product of 2-butyne and aluminium cloride has been deduced from single crystal X-ray diffraction data (1148 reflections) (a = 15.664(8); b = 10.886(4), c = 7.222(2) Å, Z = 4, space group Pnma). The aluminium chloride is coordinated via a σ-aluminium carbon bond (1.979 Å) to a non-planar tetramethylcyclobutadiene moiety. The bond length pattern indicates a charge dislocation within the four-membered ring.