Synthesis, characterisation, and X-ray structures of zinc(II) complexes bearing camphor-based ethyleneamineimines as pre-catalysts for heterotactic-enriched polylactide from rac-lactide

A series of Zn(II) complexes bearing camphor-based ethyleneamine derivatives, [(LZnCl2)-Zn-n] (L-n=[(E)-N-1-ethyl-N-2-(1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)ethane-1,2-diamine] (L-1), [(E)-N-1,N-1-diethyl-N-2-(1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)ethane-1,2-diamine] (L-2), and [(E)-N-(1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)-2-(pyrrolidin-1-yl)ethanamine] (L-3)), have been synthesised and characterised by X-ray crystallography. The isopropoxide derivatives [(LZn)-Zn-n((OPr)-Pr-i)(2)] and [(LZnCl)-Zn-n((OPr)-Pr-i)] (L-n=L-1-L-3), generated in situ, effectively polymerised rac-lactide (rac-LA) to yield poly(lactide) (PLA) with high number-average molecular weights (M-n) and narrow polydispersity indices. Zn(II) initiators with less steric bulk at the amine moiety exhibited better catalytic activities; thus, the ring-opening polymerisation (ROP) activity of the catalytic system depended largely on the steric hindrance imposed by the substituents attached to the amine moiety of the ligand. All of the complexes mediated stereoselective ROP of rac-LA in a living manner to yield PLA with high heterotacticity (P-r up to 0.81).