Lithiated amidines: syntheses and structural characterisations

Abstract

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(CH 2 ) 2 NMe 2 (tmen) or [Me 2 N(CH 2 ) 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 n 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 a change in the denticity of the donor ligand utilised can have a significant effect on the solid-state structure of the system.