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

• Published in: Angewandte Chemie International Edition Vol. 58; no. 5; pp. 1489 - 1493
• Main Authors: Schwamm, Ryan J., Anker, Mathew D., Lein, Matthias, Coles, Martyn P.
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 28.01.2019; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: aluminyl anion; Anions; Aromatic compounds; Chemistry; Chemistry, Multidisciplinary; COT ligand; cycloaddition; isomeric anions; Physical Sciences; Potassium; Reduction; Science & Technology; COT ligand; CYCLOADDITION REACTIONS; ACTIVATION; MOLECULAR-STRUCTURE; CRYSTAL-STRUCTURE; DIAMIDO-ETHER URANIUM(IV); ACTINIDE COMPLEXES; aluminyl anion; CHELETROPIC REACTIONS; ALKYL COMPLEXES; cycloaddition; CYCLOOCTATETRAENE; isomeric anions; reduction; INDEPENDENT CHEMICAL-SHIFTS; Dearomatization; 1,3,5,7-cyclooctatetraene (COT) ligand
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201811675

The potassium aluminyl complex K[Al(NONAr)] (NON=NONAr=[O(SiMe2NAr)2]2−, Ar=2,6‐iPr2C6H3) 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 μ2‐η2:η8‐bridge between Al and K, with additional K⋅⋅⋅π‐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. Uneasy lies the head that wears a crown: The initial product from the reaction of a two‐coordinate aluminyl anion with 1,3,5,7‐cyclooctatetraene (COT) contains the reduced COT‐ligand with pronounced aromatic character. Addition of 18‐crown‐6 to K[Al(NONAr)(COT)] promotes isomerization of the carbocycle to afford the 9‐aluminabicyclo[4.2.1]nona‐2,4,7‐triene anion.