Diverse coordination geometry of cobalt (II), zinc (II), and cadmium (II) complexes comprising N , N ‐bis(1H‐pyrazol‐1‐yl)methyl)amines derivatives: Synthesis, structures, and ring opening polymerization of rac ‐lactide

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 ·4H 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.