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]

Article abstract of DOI:10.1039/b210479b

The facile reaction of ZnMe2 with secondary carboxylic amides of the type PhC(O)N(R)H (R = Me 14, Prⁱ 15, Ph 16) yields PhC(O)N(R)ZnMe (R = Me 17, Prⁱ 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 Bu^tLi to afford either the lithium zincate PhC(O)N(R)Zn(Bu^t)2Li*2thf (R = Me 20, Prⁱ21) or the co-complex [PhC(O)N(Ph)Li*thf]*[PhC(O)N(Ph)N(Bu^t)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(Bu^t)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 straighforward 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.