Group 3 metal complexes based on a chiral tetradentate diamine-diamide ligand: Synthesis and use in polymerization of (d,l)-lactide and intramolecular alkene hydroamination catalysis

New amido complexes [Me2PMEN]Ln(N(SiR3)2) (Ln = Y, SiR3 = SiMe3, 2; Ln = Nd, SiR3 = SiMe3, 3; Ln = La, SiR3 = SiHMe2, 4) based on the chiral tetradentate diamine-diamide ligand [Me2PMEN]2−, derived by double deprotonation of the parent tetraamine N,N′-dimethyl-N,N′-bis[(S)-2-methylpyrrolidine]ethylenediamine ([Me2PMEN]H2, 1), have been readily prepared by amine elimination protocols. Complex 2 was shown to be active for the ring-opening polymerization of racemic-lactide at room temperature in toluene to yield isotactic-enriched polylactides (Pm up to 70%) with relatively narrow polydispersities (Mw/Mn = 1.32–1.67), but poor initiation efficiency. Complex 2 is also highly active for the room temperature hydroamination/cyclization of some aminopentene and aminohexene derivatives, though those reactions proceed with low enantioselectivities (up to 11% ee).

Graphical abstractNew chiral yttrium, lanthanum and neodymium amido complexes have been readily prepared and shown to feature interesting catalytic activities in the ring-opening polymerization of racemic-lactide at room temperature to yield isotactic-enriched polylactides and also highly active for the room temperature hydroamination/cyclization of some aminoalkenes, though those later reactions proceed with low enantioselectivities. Figure optionsDownload full-size imageDownload as PowerPoint slide