Synthesis, characterization and ε-caprolactone polymerization properties of ferrocenyl modified half-sandwich rare-earth metal complexes

Salt metathesis of RECl3 with 1 equiv. of FcC5Me4Li (Fc = ferrocenyl group), followed by the addition of 2 equiv. of LiCH2C6H4NMe2-o in THF at room temperature gave the ferrocenyl functionalized half-sandwich rare-earth metal bis(o-dimethylaminobenzyl) complexes (FcC5Me4)RE(CH2C6H4NMe2-o)2 (RE = Sc (1), Y (2), Lu (3)) in good isolated yields. These complexes were well-characterized by elemental analysis, FT-IR spectroscopy and NMR spectroscopy. The solid state structure of complex 1 was determined by single-crystal X-ray diffraction. Electrochemical study showed that the Fe(II/III) couple of the ferrocenyl moiety in complexes 1–3 was reversible. ε-Caprolactone polymerization initiated by complex 2 proceeded in a controlled fashion. However, upon addition of AgBF4 and Cp2Co, the catalytic performance could not be restored and reversible switching was highly unlikely.