S-Block metal inverse crowns: synthetic and structural synergism in mixed alkali metal-magnesium (or zinc) amide chemistry

This article focuses on the special chemistry that can take place when certain lithium (or other heavier alkali metal) amides are combined with certain magnesium (or zinc) bisamides, Some of the reaction mixtures studied follow a straightforward path leading to simple heterobimetallic compositions with predictable structures, whereas others take an unexpected turn to behave as powerful oxygen scavengers or as regioselective bases to yield novel products with unpredictable host-guest macrocyclic structures. We refer to these new compounds as 'inverse crown ethers' or 'inverse crowns' because their arrangement of Lewis acidic and Lewis basic sites is opposite to that encountered in conventional crown ether complexes. This developing phenomenon appears to be a direct result of pairing together the two distinct metal types in the same complex, as the chemistry cannot be replicated by complexes containing one or the other metal type on its own.