Extending chain growth beyond C1 → C4 in CO homologation: aluminyl promoted formation of the [C5O5]5− ligand.

(NONDipp)Al–K(TMEDA)2 (NONDipp = [O(SiMe2NDipp)2]2−, Dipp = 2,6-iPr2C6H3), containing an Al–K bond, activates and reductively couples cabon monoxide gas to form the [C4O4]4− ligand. This oxocarbon anion is thermally isomerised in the presence of CO and TMEDA. In contrast, the dimeric potassium aluminyl [K{Al(NONDipp)}]2 yields an aluminium complex containing the hitherto unknown [C5O5]5− ligand. [ABSTRACT FROM AUTHOR]