Ligand Recognition Processes in the Formation of Homochiral C3-Symmetric LnL3 Complexes of a Chiral Alkoxide

The reaction of a chiral racemic bidentate ligand HL1 (tBu(2)P(O)CH2CH(tBu)OH) with mid to late trivalent lanthanide cations affords predominantly homochiral lanthanide complexes (RRR)-[Ln(L-1)(3)] and (SSS)-[Ln(L-1)(3)]. A series of reactions are reported that demonstrate that the syntheses are under thermodynamic control, and driven by a ligand 'self-recognition' process, in which the large asymmetric bidentate L-1 ligands pack most favourably in a C-3 geometry around the lanthanide cation. The synthesis of bis(L-1) adducts [Ln(L-1)(2)X] (X = N(SiMe3)(2), OC(6)H(3)tBu-2,6) is also reported. Analysis of the diastereomer mixtures shows that homochiral (L-1)(2) complexes are favoured but to a lesser extent. The complexes Ln(L-1)(3) and [Ln(L-1)(2)(OC(6)H(3)tBu-2,6)] have been studied as initiators for the polymerization of epsilon-caprolactone and its copolymer with lactide, glycolide and its copolymer with lactide, and epsilon-caprolactam.