Cole, Marcus L., Deacon, Glen B., Forsyth, Craig, Junk, Peter C., Konstas, Kristina, Wang, Jun, Bittig, Henry, and Werner, Daniel (2013) Synthesis, structures and reactivity of lanthanoid(II) formamidinates of varying steric bulk. Chemistry: a European journal, 19 (4). pp. 1410-1420.

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Abstract

New reactive, divalent lanthanoid formamidinates [Yb(Form)₂(thf)₂] (Form=[RNCHNR]; R=o-MeC₆H₄ (o-TolForm; 1), 2,6-Me₂C₆H₃ (XylForm; 2), 2,4,6-Me₃C₆H₂ (MesForm; 3), 2,6-Et₂C₆H₃ (EtForm; 4), o-PhC₆H₄ (o-PhPhForm; 5), 2,6-iPr₂C₆H₃ (DippForm; 6), o-HC₆F₄ (TFForm; 7)) and [Eu(DippForm)₂(thf)₂] (8) have been prepared by redox transmetallation/protolysis reactions between an excess of a lanthanoid metal, Hg(C₆F5)₂ and the corresponding formamidine (HForm). X-ray crystal structures of 2–6 and 8 show them to be monomeric with six-coordinate lanthanoid atoms, chelating N,N′-Form ligands and cis-thf donors. However, [Yb(TFForm)₂(thf)₂] (7) crystallizes from THF as [Yb(TFForm)₂(thf)₃] (7 a), in which ytterbium is seven coordinate and the thf ligands are "pseudo-meridional". Representative complexes undergo C[BOND]X (X=F, Cl, Br) activation reactions with perfluorodecalin, hexachloroethane or 1,2-dichloroethane, and 1-bromo-2,3,4,5-tetrafluorobenzene, giving [Yb(EtForm)₂F]₂ (9), [Yb(o-PhPhForm)₂F]₂ (10), [Yb(o-PhPhForm)₂Cl(thf)₂] (11), [Yb(DippForm)₂Cl(thf)] (12) and [Yb(DippForm)₂Br(thf)] (16). X-ray crystallography has shown 9 to be a six-coordinate, fluoride-bridged dimer, 12 and 16 to be six-coordinate monomers with the halide and thf ligands cis to each other, and 11 to have a seven-coordinate Yb atom with "pseudo-meridional" unidentate ligands and thf donors cis to each other. The analogous terbium compound [Tb(DippForm)₂Cl(thf)₂] (13), prepared by metathesis, has a similar structure to 11. C[BOND]Br activation also accompanies the redox transmetallation/protolysis reactions between La, Nd or Yb metals, Hg(2-BrC₆F₄)₂, and HDippForm, yielding [Ln(DippForm)₂Br(thf)] complexes (Ln=La (14), Nd (15), Yb (16)).

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