Reduction of Sterically Hindered β-Diketiminato Europium(iii) Complexes by the β-Diketiminato Anion: A Convenient Route for the Synthesis of β-Diketiminato Europium(ii) Complexes

Abstract

The metathesis reaction of anhydrous EuCl₃ with sodium salt of bulky β-diketiminato NaL (L = [N(2, 4, 6- Me₃C₆H₂)C(Me)]₂CH⁻, L^{2, 4, 6-Me3}; [N(2,6-ⁱPr₂C₆H₃)C(Me)]₂CH⁻, L^2, 6-ipr2 and [(2, 6-ⁱPr₂C₆H₃)NC(Me)CHC(Me)N(C₆H₅)]⁻, L^2, 6-ipr2_Ph) in THF at 60 °C afforded the corresponding Eu^II complexes: Eu^II(L^{2, 4, 6-Me3})₂(THF) (1), Eu^II(L^2, 6-ipr2)₂ (2) and Eu^II(L^2, 6-ipr2_Ph)₂ (5) with the formations of dimers (L^{2, 4, 6-Me3})₂ (3) and (L^2, 6-ipr2)₂ (4) for the former two reactions and proligand L^2, 6-ipr2_PhH (6) for the latter one. Compounds 1–6 were confirmed by an X-ray crystal structure analysis. The central metal Eu^II in 1 is coordinated by two monoanionic L^{2, 4, 6-Me3} ligands and one THF molecule in a trigonal bipyramid. The Eu^II in each of 2 and 5 is ligated by two monoanionic ligands to form a tetrahedral geometry. The BVS (Bond Valence Sum) calculation indicates the oxidation state of Eu in all the three complexes is 2+ (2.12 for 1, 1.86 for 2 and 1.99 for 5). The isolation of dimers of (L^{2, 4, 6-Me3})₂ and L^2, 6-ipr2)₂ and proligand L^2, 6-ipr2_PhH demonstrates that the reducing agent in the present reduction of a Eu^III ion to a Eu^II ion might be the (L^{2, 4, 6-Me3})⁻, (L^2, 6-ipr2)⁻ and (L^2, 6-ipr2_Ph)⁻, respectively. The possible mechanism for the reduction pathway is presented.