Mono-guanidinate complexes of lanthanum: Synthesis, structure and their use in lactide polymerization

Article abstract of DOI:10.1039/b008164g

La[N(SiMe₃)₂]₃ reacted with 1,3-dicyclohexylcarbodiimide in refluxing toluene to yield the mono-guanidinate complex La[CyNC(N(SiMe₃)₂)NCy](N(SiMe₃) ₂)₂ 1. Compound 1 is monomeric in solution; X-ray structural analysis reveals an unassociated complex in the solid state, with a four-coordinate lanthanum center. Complex 1 reacts with 2,6-di-tert-butylphenol (2 equivalents) in cold pentane to yield the bis(phenoxide) complex La[CyNC(N(SiMe₃)₂)NCy]-(OC₆H₃ ^tBu₂-2,6)₂. X-Ray analysis indicates a similar structure to that of 1, with a four-coordinate lanthanum center coordinated by a single guanidinate ligand and two phenoxide groups. This compound catalyses the ring-opening polymerization of D,L-lactide to polylactide. Although high molecular weight polymer is obtained, polydispersities are broad and no control over the stereochemistry of the polymer is observed. The Royal Society of Chemistry 2001.