The ring-stacking principle in organolithium chemistry: its development through the isolation and crystal structures of hexameric iminolithium clusters (RR'C=NLi)6 (R'=Ph, R=But or Me2N; R=R'=Me2N or But)

Synthetic and X-ray crystallographic studies on two new iminolithium compounds, [But(Ph)CNLi]6(1) and [Me2N(Ph)CNLi]6(2), have revealed, in conjunction with previously reported work on [(Me2N)2CNLi]6(3) and (But2CNLi)6(4), a family of hexameric iminolithium species. All four compounds have remarkably similar solid-state structures based on slightly folded chair-shaped Li6 cores, the six smaller (isosceles) Li3 triangular faces of which are bridged by three-electron imino ligands through electron-deficient bonds. The precise determination of the structures of (1) and (2) has revealed features which were not apparent in the earlier limited and less fully refined structural studies on (3) and (4). Recognition of such features and their detailed analysis leads to a ring-stacking principle which envisages the formation of these hexameric structures from two slightly puckered trimeric rings, (RR′CNLi)3, brought together in a staggered arrangement. Extension of this principle allows the rationalisation of many other structures in lithium chemistry and facilitates structural predictions.