Homoleptic yttrium and lanthanide complexes of aminotroponiminates and aminotroponates: experimental and theoretical studies

Abstract

Density functional theory (DFT) calculations were performed for the homoleptic aminotroponiminate complexes [Ln{C₇H₅(NPrⁱ)₂}₃] (Ln = Y or Sm) in order to get structural and energetic information about the possible isomers. The calculations predict a propeller-shaped chiral isomer of D₃ symmetry as lowest in energy. Two less stable isomers turned out to be stationary points of higher order. One is likely to be close to a structure acting as intermediate in the mechanism of rapid racemisation observed by NMR studies. Based on these results experimental and DFT computational studies of homoleptic lanthanide complexes with the new ligand system aminotroponate C₇H₅(NPrⁱ)O^– were carried out. This related but asymmetric ligand results in a slower isomerisation and thus detection of the concerned species: ¹H NMR experiments showed an equilibrium of several [Y{C₇H₅(NPrⁱ)O}₃] isomers in solution, in agreement with the computational results.