Chiral Mono(borohydride) Complexes of Scandium and Lutetium and Their Catalytic Activity in Ring-Opening Polymerization of DL-Lactide

The enantiopure mono(borohydride) rare-earth complexes [Ln{(S)-PETA)}(2)(BH4)] (Ln = Sc (1), Lu (2); PETA = N,N'-bis((S)-1-phenylethyl)-tert-butylamidinate) are reported. The synthesis was achieved by salt metathesis reactions of the homoleoptic tris(borohydrides) [Ln(BH4)(3)(thf)(n)] and (S)-LiPETA. Complexes 1 and 2 were fully characterized, including single-crystal X-ray diffraction. Compounds 1 and 2 were evaluated as initiators for the ring-opening polymerization (ROP) of racemic lactide. Both 1 and 2 were found to be active in the ROP of DL-lactide. Polymerizations carried out in toluene show a higher activity for 2 but a lower selectivity in comparison to the scandium derivative.