New motifs in lithium zincate chemistry: a solid-state structural study of PhC(O)N(R)ZnR2Li·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, Pri15, Ph 16) yields PhC(O)N(R)ZnMe (R = Me 17, Pri18, 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 ButLi to afford either the lithium zincate PhC(O)N(R)Zn(But)2Li·2thf (R = Me 20, Pri21) or the co-complex [PhC(O)N(Ph)Li·thf]·[PhC(O)N(Ph)Zn(But)2Li·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(But)2Li 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.