Synthesis and structural characterisation of divalent transition metal complexes containing an unsymmetrical benzamidinate ligand

Abstract

The unsymmetrical benzamidinate ligand [PhC(NSiMe₃)(NAr)]⁻ (Ar = 2,6-Me₂C₆H₃), denoted L⁻, and its lithium derivative [LiL(TMEDA)] (1) (TMEDA = N,N,N′,N′-tetramethylethylenediamine) have been prepared. Treatment of 1 with MCl₂ (M = Mn, Co, Fe or Ni) afforded the corresponding divalent transition metal benzamidinates with interesting molecular structures. The reaction of two equivalents of 1 with MnCl₂ or CoCl₂ afforded the centrosymmetric binuclear complexes [(ML₂)₂·(TMEDA)] (M = Mn 2, Co 5). On the other hand, the reaction of FeCl₂ with 1, in an appropriate stoichiometric ratio, led to the mononuclear mono(benzamidinate) [FeL(Cl)(TMEDA)] (3) and the bis(benzamidinate) [FeL₂(TMEDA)] (4) complexes. The addition of two equivalents of 1 to NiCl₂ yielded the mononuclear [NiL₂] (6). X-Ray crystallography revealed that the κ²-benzamidinate ligand L⁻ is bonded to the metal centre of these complexes in an unsymmetrical fashion. The TMEDA ligand in 2–5 exhibits different coordination modes. It acts as a chelating ligand in 3, as a monodentate ligand in 4, and as an unusual N,N′-bridging ligand in 2 and 5.