Synthesis and Characterization of Lanthanide( III ) Bis(guanidinate) Derivatives and the Catalytic Activity of Methyllanthanide Bis(guanidinate) Complexes for the Polymerization of ϵ‐Caprolactone and Methyl Methacrylate

The synthesis and structure of new lanthanide complexes with the guanidinate ligand [(Me 3 Si) 2 NC(N i Pr) 2 − ] are described. Reaction of a THF slurry of LnCl 3 with a hexane solution of [(SiMe 3 ) 2 NC(N i Pr) 2 ]Li ( 1 ) in a 1:2 molar ratio afforded the new soluble organolanthanide complexes [(SiMe 3 ) 2 NC(N i Pr) 2 ]Ln(μ‐Cl) 2 Li(THF) 2 [Ln = Yb ( 2 ), Nd ( 3 )]. Alkylation of 2 and 3 with 2 equiv. of MeLi in hexane gave [(SiMe 3 ) 2 NC(N i Pr) 2 ]Ln(μ‐Me) 2 Li(TMEDA) [Ln = Yb ( 4 ), Nd ( 5 )] in good yield as crystalline solids. The molecular structures of 2 and 5 were determined by single‐crystal X‐ray analysis. The lanthanide ions in these complexes display a distorted pseudo‐octahedral coordination geometry. Complexes 4 and 5 exhibited extremely high activity for the ring‐opening polymerization of ϵ‐caprolactone to give high molecular weight polymers. Complex 5 also showed good catalytic activity for the syndiotactic polymerization of methyl methacrylate. (© Wiley‐VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2002)