Zwitterionic bis(phenolate) amine lanthanide complexes for the ring-opening polymerisation of cyclic esters

The reaction of Sm{N(SiMe3)(2)}(3) with the bis(phenol) amines H2O2NR (H2O2NR = RCH2CH2N(2-HO-3,5-C6H2t Bu-2)(2); R = OMe, NMe2 or Me) gave exclusively zwitterions Sm(O2NR)- (HO2NR). For R= OMe or NMe2 these were efficient catalysts for the ring-opening polymerisation of epsilon-caprolactone and D,L-lactide with a tendency to form cyclic esters; in contrast, no polymerisation was observed for R = Me.