Synthesis and structures of lithium, aluminium, gallium and lanthanide amidinates containing a γ-pendant amine functionality

Abstract

Lithium, aluminium, gallium, lanthanum and cerium complexes of the new amidinato ligand ⁻N(SiMe₃)C(Ph)N(CH₂)₃NMe₂ (≡L⁻), having a γ-pendant amine functionality, have been prepared. The dimeric lithium amidinate 1 was obtained in four steps from 1-amino-3-(dimethylamino)propane. Using 1 and MCl₃ in appropriate stoichiometry led to the mononuclear M(L)Cl₂ (M = Al 2 or Ga 3) and the dinuclear [{M(L)₂(μ-Cl)}₂] (M = La 4 or Ce 5). Structures of four of these (1, 2, 3 and 5) have been studied by X-ray crystallography. In crystalline 1 each amidinato ligand L⁻ is chelating with respect to one of the lithium atoms and bridging by virtue of its pendant γ-tertiary nitrogen atom to the second Li atom. In 2 and 3, by contrast, L⁻ behaves as a tripodal chelating ligand, whereas in crystalline 5 the seven-co-ordinate Ce atom is bound by two bidentate benzamidinato fragments and only one of the pendant amines.