Synthesis and molecular structures of YbII and Ca bis(amidinate) complexes containing the tridentate amidinate ligand [2,6-Pri2C6H3NC(But)NC6H4OMe-2]

Abstract

New bis(amidinate) complexes of calcium, [2,6-Prⁱ₂C₆H₃NC(But)NC₆H₄OMe-2]₂Ca(DME) (2), and divalent ytterbium, [2,6-Prⁱ₂C₆H₃NC(But)NC₆H₄OMe-2]₂Yb (4), were synthesized by the transamination of the bis(amide) derivatives [(Me₃Si)₂N]₂M(THF)₂ (M = Ca, Yb) with two equivalents of amidine 2,6-Prⁱ₂C₆H₃N=C(But)N(H)C₆H₄OMe-2, in which one nitrogen atom bears an o-methoxyphenylene moiety capable of coordinating a metalion. An X-ray diffraction study showed that, despite very similar ionic radii of Ca²⁺ and Yb²⁺, the amidinate ligands in complexes 2 and 4 bind to these ions in different coordination modes. In the calcium complex, both ligands adopt a κ²-N, O-chelating coordination mode. In the divalent ytterbium compound, one ligand is chelating and binds to the metalion in a κ²-N, O-coordination mode, while the second ligand is coordinated via both the N and O (κ²) atoms and the arene ring of the 2,6-Prⁱ₂C₆H₃ moiety (η⁶-coordination mode).