Synthesis and Structure of the (µ2-OP(O)Ph2)-Linked Dimeric Amide Lanthanum Complex {[CP(O)Ph2]La[N(SiMe3)2](µ2-OP(O)Ph2)}2 Bearing the Tridentate Heteroscorpionate Ligand. Investigation of the Catalytic Activity in rac-Lactide and ε-Caprolactone Polymerization

The dimeric amide lanthanum complex {[ CP(O)Ph 2 ]La[N(SiMe 3 ) 2 ](µ 2 -OP(O)Ph 2 )} 2 (Pzl Me2 is 3,5-dimethylpyrazole) bearing the N , N , O -tridentate heteroscorpionate ligand is synthesized. As found by X-ray diffraction (XRD) (CIF file CCDC no. 2212274), the complex is binuclear and its lanthanum ions are linked by two bridging monoanionic diphenyl phosphinate ligands. The synthesized lanthanum complex demonstrates a high catalytic activity in the polymerization with ring opening of rac -lactide and ε-caprolactone providing the quantitative conversion of 500 equivalents of the monomer to the polymer at room temperature within 360–720 min for rac -lactide and 10–30 min for ε-caprolactone. The formed polylactides are characterized by the atactic microstructure ( P r = 0.54–0.56) and polydispersity indices (PDI) of 1.6–2.5, whereas for polycaprolactone PDI = 2.1–2.8.