Lithiated amidines: Syntheses and structural characterisations

The reaction of a toluene solution of PhNC(Ph)NHPh (N,N'-diphenylbenzamidine) with n-butyllithium gave the toluene-solvated amidinolithium compound {Li[PhNC(Ph)NPh]}_n. Similarly the same reaction performed in the presence of the Lewis-base donors (Me₂N)₃PO (hmpa), Me₂N(CH₂)₂NMe₂ (tmen) or [Me₂N(CH₂)₂]₂ (pmdien) yielded the am{Li[PhNC(Ph)NPh·hmpa]}₂ 2, {Li[PhNC(Ph)NPh]·tmen} 3 and {Li[PhNC(Ph)NPh]. pmdien} 4 respectively. In addition the reaction of a toluene solution of the related amidine PhNC(Me)NHPh (N,N′-diphenylacetamidine) with LiBu in the presence of hmpa afforded {Li[PhNC(Me)NPh]·hmpa}₂ 5. The solid-state structures of 2-5, which have been resolved by single-crystal X-ray diffraction methods, show both similarities and differences The complexes 3 and 4, which contain the di- and tri-dentate ligands tmen and pmdien respectively, are monomeric, whilst use of the unidentate Lewis base hmpa results in dimers 2 and 5. However, the way in which dimerisation is achieved differs. The co-ordination geometry about the lithium cation is clearly influenced by the choice of donor and as such shows how change in the denticity of the donor ligand utilised can have a significant effect on the solid-state structure of the system