Lanthanum Bis(amidinate) Amido Complex {2-[Ph2Р(O)]C6H4NC(But)N(2,6-Me2C6H3)}2LaN(SiMe3)2: Synthesis, Structure, and Catalytic Activity in Ring-Opening Polymerization of rac-Lactide and ε-Caprolactone

The La(III) bis(amidinate) amido complex {2-[Ph2Р(O)]C6H4NC(But)N(2,6-Me2C6H3)}2LaN(SiMe3)2 (I) was synthesized by the reaction of 2-[Ph2Р(O)]C6H4NHC(But)=N(2,6-Me2C6H3) (HL) and La[N(SiMe3)2]3 in 2 : 1 molar ratio and isolated in 74% yield. X-ray analysis revealed that in I both monoanionic amidinate ligands are κ3-N,N,O-coordinated to La(III) ion. Complex I demonstrates high catalytic activity in ring-opening polymerization of cyclic esters and enables 100% conversion of 100–300 equiv of rac-lactide in 30 min or 100–500 equiv of ε-caprolactone in 1 min providing highly controlled polymerization. The obtained polymeric samples feature linear dependence of molecular weight vs. the monomer loading and rather narrow polydispersity (Mw/Mn = 1.36–1.88).