Co(ii), Zn(ii), and Cd(ii) complexes supported by bis-pyrazolyl ligands were applied to the ring-opening polymerization of rac-lactide to produce heterotactic polylactides (PLAs) with superior heterotactic bias i.e. Pr up to 0.94 at −25 °C.

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A series of six new complexes of Co (II), Zn (II), and Cd (II) supported by bis (1H-pyrazol-1-yl)methyl)amine derivatives (N,N-bis((1H-pyrazol-1-yl)methyl)-1-phenylethanamine (L A ), N,N-bis((1H-pyrazol-1-yl)methyl)-1-(furan-2-yl) methanamine (L B ), and N,N-bis((1H-pyrazol-1-yl)methyl)-4-isopropylaniline (L C ) synthesized. The direct chelation of the ligands (L n = L A − L C ) with ZnCl 2 , CoCl 2 .6H 2 O, and CdBr 2 Á4H 2 O produced [L n MX 2 ] (L n = L A − L C ; M = Zn, Co; X = Cl; M = Cd, X = Br) and [L C Cd(μ-Br)Br] 2 in high yields. Structural studies revealed that [L n ZnCl 2 ] (L n = L A − L C ), [L A CdBr 2 ], and [L C CoCl 2 ] adopted the distorted tetrahedral geometry, whereas [L A CoCl 2 ] and [L C Cd(μ-Br)Br] 2 adopted a distorted square pyramidal geometry by coordinating with corresponding ligands in a bidentate fashion. Additionally, [L B CdBr 2 ] possessed a distorted trigonal bipyramidal geometry that was obtained by the chelation with corresponding ancillary ligands in the tridentate coordination mode. The dimethyl derivatives of [L n MMe 2 ] (L n = L A − L C ; M = Zn, Co; X = Cl; M = Cd, X = Br), which were generated in situ, were employed to catalyze the ring-opening polymerization (ROP) of rac-lactide (rac-LA). Hetero-enriched polylactides (PLAs) were furnished with all these complexes (Complex [L B ZnCl 2 ] produced PLA with superior heterotactic bias (P r of up to 0.93) at −25 C). PLAs with wide-ranged polydispersity indices (PDI = 1.43-1.54) were produced in all the cases irrespective of the M (II) center and variations in ancillary ligands. K E Y W O R D S (pyrazolyl)amine ligand, diverse coordination environment, hetero-enriched poly (lactide), ringopening polymerization