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) 1. Similarly the same reaction performed in the presence of the Lewis-base donors (Me(2)N)(3)PO (hmpa), Me(2)N(CH2)(2)NMe(2) (tmen) or [Me(2)N(CH2)(2)](2)NMe (pmdien) yielded the amidinolithium complexes {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(II) 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.