Zinc complexes of chiral ligands obtained from methylbenzylamine

Condensation of S-methylbenzylamine with 2 equiv. of 2,4-tert-butylphenol yielded the chiral tridentate ligand 2H2, which formed the dimetallic complex (2)(k-N,(μ-O)2ZnEt)((μ-O)2ZnEt), 3, upon reaction with ZnEt2. Reaction of the chiral Schiff base ligand, 4H, obtained from condensation of salicylaldehyde and S-methylbenzylamine, with ZnEt2 yielded (4)2Zn, 5, or (4)ZnEt, 6, respectively. Deprotonation of 4H with NaH afforded tetrameric {(4)Na}4, 7. Complexes 3, 5 and 7 were characterized by single crystal diffraction studies and tested as initiators in the polymerization of rac-lactide. Complexes 3 and 5 showed only low to moderate activity. All complexes yielded essentially atactic polymers with minor contents of heterotactic enchainment.

Several zinc complexes with chiral ligands based on S-methylbenzylamine were synthesized and characterized by X-ray diffraction analysis. They proved to be active, but unselective catalysts for the polymerization of rac-lactide.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis and characterization of a new tridentate, chiral ligand.
► Synthesis and characterization of 3 chiral zinc complexes and one chiral sodium complex.
► X-ray diffraction studies on 3 of these complexes.
► Application of 3 of these complexes in rac-lactide polymerization.