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

Abstract

The syntheses and crystal structures of two iminolithium adducts [Bu^t₂CNLi·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.