Lanthanum complexes containing a bis(phenolate) ligand with a ferrocene-1,1'-diyldithio backbone: synthesis, characterization, and ring-opening polymerization of rac-lactide.

Lanthanum complexes [(L)LaX] (X = N(SiMe3)2, O(i)Pr , BH4) supported by a ferrocene-based (OSSO)-type ligand LH2 were synthesized and characterized by elemental analysis, NMR spectroscopy and cyclic voltammetry. The structure of was confirmed by single crystal X-ray diffraction. These complexes were highly active initiators for the ring-opening polymerization of rac-lactide (rac-LA). The activity depended on the initiating group in the order of ≈ > . The activities of and during polymerization were controlled in situ with external redox reagents by reversibly switching the oxidation state of the iron center.