Synthesis, characterization and X-ray structures of enatiopure-diamine zinc(II) complexes as pre-catalysts for stereoselective production of poly(rac-lactide)

Two novel dichlorozinc complexes, (peeda)ZnCl2 and (pepda)ZnCl2, where peeda is N1,N2-bis{(R)-1-phenylethyl}ethane-1,2-diamine and pepda is N1,N3-bis{(R)-1-phenylethyl}propane-1,3-diamine, were synthesised and characterised by X-ray diffraction. Dialkyl derivatives of these compounds, generated in situ, efficiently initiated the ring-opening polymerisation (ROP) of rac-lactide (rac-LA). The backbone links, composed of diamine units, had a significant influence on the degree of stereoselectivity in the resulting heterotactic polylactide (PLA). Increased flexibility of the diamine backbone resulted in enhanced heterotacticity. (pepda)ZnMe2 produced heterotactic PLA with a Pr of 0.78 at −25 °C.

Graphical abstractNew dichloro zinc complexes bearing homochiral diamine ligands were prepared and characterized by spectroscopic methods and X-ray diffraction analysis. Dialkyl derivatives of the zinc complexes initiated the ring-opening polymerisation (ROP) of rac-lactide (rac-LA) to give heterotactic-enriched PLA. The backbone links, composed of diamine units, had a significant influence on the degree of stereoselectivity in the resulting heterotactic polylactide.Figure optionsDownload full-size imageDownload as PowerPoint slide