Synthesis of mixed alkali-metal-zinc enolate complexes derived from 2,4,6-trimethylacetophenone: new inverse crown structures

The solution and solid-state characterization of two new mixed alkali-metal−zinc enolate compounds is reported. These compounds are prepared by reaction of the relevant mixed-metal base [MZn(HMDS)3] (M = Na, K; HMDS = 1,1,1,3,3,3-hexamethyldisilazide) with a stoichiometric amount of the sterically demanding ketone 2,4,6-trimethylacetophenone. Thus, the new mixed-metal enolate compounds [Na2Zn2{OC(=CH2)Mes}6{OC(CH3)Mes}2] (2) and [K2Zn2{OC(=CH2)Mes}6(CH3Ph)2] (3) are obtained for M = Na, K, respectively. X-ray crystallographic studies reveal that both compounds adopt the same structural motif, which define them as inverse crown complexes, a cationic eight-membered [(MOZnO)2]2+ ring which hosts in its core two additional enolate ligands. Each Zn center is bonded to four anionic enolate ligands framing the structure, whereas the alkali metals form much weaker interactions with the oxygen atoms and complete their coodination sphere by bonding to a neutral molecule, an unenolised ketone for M = Na or toluene for M = K.