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]

Abstract

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 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)Zn(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 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.