Reduction vs. Addition: The Reaction of an Aluminyl Anion with 1,3,5,7-Cyclooctatetraene

The potassium aluminyl complex K[Al(NONAr)](NON = NONAr = [O(SiMe2NAr)2](2-), Ar = 2,6-iPr(2)C(6)H(3)) reacts with 1,3,5,7-cyclooctatetraene (COT) to give K[Al(NONAr)(COT)]. The COT-ligand is present in the asymmetric unit as a planar mu(2)-eta(2):eta(8)-bridge between Al and K, with additional K center dot center dot center dot pi-aryl interactions to neighboring molecules that generate a helical chain. DFT calculations indicate significant aromatic character, consistent with reduction to [COT](2-). Addition of 18-crown-6 causes a rearrangement of the C8-carbocycle to form the isomeric 9-aluminabicyclo[4.2.1]nona-2,4,7-triene anion.