Probing the Extremes of Covalency in M−Al bonds: Lithium and Zinc Aluminyl Compounds

Synthetic routes to lithium, magnesium, and zinc aluminyl complexes are reported, allowing for the first structural characterization of an unsupported lithium–aluminium bond. Crystallographic and quantum-chemical studies are consistent with the presence of a highly polar Li−Al interaction, characterized by a low bond order and relatively little charge transfer from Al to Li. Comparison with magnesium and zinc aluminyl systems reveals changes to both the M−Al bond and the (NON)Al fragment (where NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene), consistent with a more covalent character, with the latter complex being shown to react with CO₂ via a pathway that implies that the zinc centre acts as the nucleophilic partner.