Nitrogen-containing lanthanide complexes: initiators or real catalysts forthe epsilon-caprolactone polymerisation?

Nitrogen-based organolanthanide complexes: (Siam)(3)Ln (Ln = Yb, 1a, Sm. 1b ), (C5H4CMe2)(2)Sm(Siam), 2, (COT)SmN(SiMe3)(2), 4 (Siam = PhC(NSiMe3)(2), COT = C8H8), are very efficient towards polymerisation of epsilon -caprolac tone. Mechanistic studies on the basis of NMR experiments show that the com plexes 1a, 1b and 2 behave as real catalysts, while 4 is the precursor of a heterogeneous initiator. The hapticity of thr nitrogen ligand may be relat ed to the formation of cyclic oligomers, (C) 2000 Academie des sciences / E ditions scientifiques et medicales Elsevier SAS.