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

Abstract

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.