New motifs in lithium zincate chemistry:: a solid-state structural study of PhC(O)N(R)ZnR′2Li•2thf (R, R′ = alkyl, aryl) and [PhC(O)N(Ph)Li•thf]•[PhC(O)N(Ph)Zn(But)2Li•thf]

The facile reaction of ZnMe2 with secondary carboxylic amides of the type PhC(O) N( R) H (R = Me 14, Pr-i 15, Ph 16) yields PhC(O) N(R) ZnMe (R = Me 17, Pr-i 18, Ph 19). These complexes describe a hexamer (for 17) and tetramers (for 18 and 19) in the solid state which are best viewed as stacks of cyclic trimers and dimers, respectively. In turn, 17-19 react with (BuLi)-Li-t to afford either the lithium zincate PhC(O) N(R) Zn(Bu-t)(2) Li.2thf (R = Me 20, Pr-i 21) or the co-complex [PhC(O) N( Ph) Li.thf].[PhC(O) N(Ph) Zn(Bu-t)(2) Li.thf] 22. In the solid state both 20 and 21 reveal dimeric structures based on a (LiO)(2) core in which each alkali metal centre is doubly thf-solvated and trivalent zinc centres reside peripheral to the cluster. The structure of 22 reveals an adduct in which a dimeric lithium (carboxylic) amide core interacts with two PhC(O) N(Ph) Zn(Bu-t)(2)Li molecules, affording a structure intermediate between a ladder and an "open" pseudo-cubane. This is the first full characterisation of a complex between an alkali metal zincate and another organometallic species and it affords new insights into how these two classes of molecule interact. The straightforward formation of [PhC(O) N(R) ZnMe2](-) (R = Me 23, Ph 24) ions has been successfully achieved by treating the appropriate lithium carboxylic amide with ZnMe2. In the solid-state, PhC(O) N(Ph) ZnMe2Li.2thf 24 is revealed to be isostructural with 20 and 21.