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 (LA), N,N‐bis((1H‐pyrazol‐1‐yl)methyl)‐1‐(furan‐2‐yl)methanamine (LB), and N,N‐bis((1H‐pyrazol‐1‐yl)methyl)‐4‐isopropylaniline (LC) synthesized. The direct chelation of the ligands (Ln = LA − LC) with ZnCl2, CoCl2.6H2O, and CdBr2·4H2O produced [LnMX2] (Ln = LA − LC; M = Zn, Co; X = Cl; M = Cd, X = Br) and [LCCd(μ‐Br)Br]2 in high yields. Structural studies revealed that [LnZnCl2] (Ln = LA − LC), [LACdBr2], and [LCCoCl2] adopted the distorted tetrahedral geometry, whereas [LACoCl2] and [LCCd(μ‐Br)Br]2 adopted a distorted square pyramidal geometry by coordinating with corresponding ligands in a bidentate fashion. Additionally, [LBCdBr2] 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 [LnMMe2] (Ln = LA − LC; 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 [LBZnCl2] produced PLA with superior heterotactic bias (Pr 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. Co(II), Zn(II), and Cd(II) complexes ligated to N‐aromatic group substituted N,N‐bis(1H‐pyrazolyl‐1‐methyl)aniline derivatives have been employed as pre‐catalysts in catalyzing ring opening polymerization of rac‐LA. Heterotactic PLAs have been provided with all these complexes, with complex [LBZnCl2] yielding superior heterotactic bias (Pr up to 0.93) at ‐25−C.