Synthesis and structures of amine bis(phenolate) lanthanide thiolates and their application in the polymerization of ε-caprolactone

Reaction of anhydrous LnCl3 with 1 equivalent of LNa2 (L2− = [Me2NCH2CH2CH2N{CH2-(3,5-tBu2–C6H2–2-O)}2]2−) and 1 equivalent of CpNa (Cp− = C5H5−) in THF firstly, then with 1 equivalent of p-thiocresol, leads to the lanthanide thiolates of LLn(SC6H4-p-Me)(THF) (Ln = Sm (1), Er (2), Yb (3)). They were characterized by infrared spectra, elemental analyses and X-ray crystallography. Complexes 1–3 are monomers. The L2− dianion ligand coordinates with the lanthanide ion in an O,N,N,O-tetradentate mode. All the complexes can catalyze the ring-opening polymerization of ε-caprolactone, and the activity decreases in the order of 1(Sm) > 2(Er) > 3(Yb). The polymer’s polydispersity index (PDI) by complexes 1–3 is in the range of 1.3–1.5, less than that by [(MeCp)2Sm(SC6H5)(THF)]2. The initiation mechanism for the polymerization was discussed.