A Comparative Study on the Reactivity of Tris-β-Diketiminate Ytterbium Complexes: Steric Effect of β-Diketiminato Ligands

A series of tris-β-diketiminate ytterbium complexes with the general formula [YbL 3 ] {L = [N(C 6 H 5 )C(Me)] 2 CH - , L H (1); [N(4-MeC 6 H 4 )C(Me)] 2 CH - , L 4-Me (2), and [N(2-MeC 6 H 4 )-C(Me)] 2 CH - , L 2-Me (3)) were synthesized and structurally characterized. All complexes have longer Yb-N bond lengths than other YbL-containing derivatives, and complex 3 has the longest average Yb-N bond length. A comparative study on the reactivity of complexes 1-3 revealed that complex 3 was a highly active catalyst for the polymerization of e-caprolactone and L -lactide, as well as for the addition of amines to carbodiimides, whereas both complexes 1 and 2 were almost inactive under the same conditions. The active sequence is consistent with the distance of the Yb-N bond, which is reflected in the sterically induced activation of the bulky tris-β-diketiminate ytterbium complexes.