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

The metathesis reaction of anhydrous EuCl3 with sodium salt of bulky β-diketiminato NaL (L = [N(2, 4, 6- Me3C6H2)C(Me)]2CH−, L2, 4, 6-Me3; [N(2,6-iPr2C6H3)C(Me)]2CH−, L2, 6-ipr2 and [(2, 6-iPr2C6H3)NC(Me)CHC(Me)N(C6H5)]−, L2, 6-ipr2Ph) in THF at 60 °C afforded the corresponding EuII complexes: EuII(L2, 4, 6-Me3)2(THF) (1), EuII(L2, 6-ipr2)2 (2) and EuII(L2, 6-ipr2Ph)2 (5) with the formations of dimers (L2, 4, 6-Me3)2 (3) and (L2, 6-ipr2)2 (4) for the former two reactions and proligand L2, 6-ipr2PhH (6) for the latter one. Compounds 1–6 were confirmed by an X-ray crystal structure analysis. The central metal EuII in 1 is coordinated by two monoanionic L2, 4, 6-Me3 ligands and one THF molecule in a trigonal bipyramid. The EuII 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 (L2, 4, 6-Me3)2 and L2, 6-ipr2)2 and proligand L2, 6-ipr2PhH demonstrates that the reducing agent in the present reduction of a EuIII ion to a EuII ion might be the (L2, 4, 6-Me3)−, (L2, 6-ipr2)− and (L2, 6-ipr2Ph)−, respectively. The possible mechanism for the reduction pathway is presented.