The syntheses and crystal structures of two iminolithium adducts: (Ph2CNLi·NC5H5)4, a tetrameric pseudo-cubane formed by stacking two (LiN)2 four-membered rings, and [But2CNLi·OP(NMe2)3]2, a dimer prevented sterically from stacking

The syntheses and crystal structures of two iminolithium adducts [But2CNLi·OP(NMe2)3]2(1)[OP(NMe2)3= hexamethylphosphoramide (hmpa)] and (Ph2CNLi·NC5H5)4(2)(NC5H5= pyridine) are described. Adduct (1) contains a centrosymmetric planar (LiN)2 ring, with Li–N distances of 1.923(6) and 1.948(6)Å, and a ring angle at nitrogen of 75.4(3)°. Unexpectedly, the C2CN skeletal planes of its imino ligands are twisted 58.6(6)° with respect to the (LiN)2 ring plane, apparently to accommodate the bulky hmpa ligands, so preventing the (LiN)2 rings from stacking to form an (LiN)4 cubane structure. In contrast, adduct (2), with sterically compatible Ph2CN and NC5H5 ligands, has an (LiN)4 cubane structure with three distinct categories of metal–nitrogen distance (averaging 2.03,2.08, and 2.16 Å respectively) and ligand orientations that support an interpretation of this cubane in terms of two stacked (LiN)2 four-membered ring systems.