Synthesis, structures, and catalytic efficiency in ring opening polymerization ofrac-lactide with tridentatevs.bidentate cobalt(ii), zinc(ii), and cadmium(ii) complexes containingN-substitutedN,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)amine ligands

A series of Co(ii), Zn(ii), and Cd(ii) complexes supported by 1-(3,5-dimethyl-1H-pyrazol-1-yl)-N-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-N-(furan-2-ylmethyl)methanamine (L_A) andN,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-isopropylaniline (L_B) were synthesized. The direct chelation of CoCl₂·6H₂O, ZnCl₂, and CdBr₂·4H₂O by the ligands produced[L_nMX₂](L_n= L_Aor L_B; M = Zn or Co, with X = Cl; M = Cd, with X = Br) complexes in high yields. Structural studies revealed that[L_BCoCl₂]and[L_BZnCl₂]adopted distorted tetrahedral geometries, as L_Bcoordinated the metal centers in a bidentate fashion, while L_Acoordinated the metal centers in a tridentate fashion through the nitrogen atoms of the pyrazole and amine moieties, so that[L_ACoCl₂]and[L_AZnCl₂]exhibited trigonal bipyramidal geometries and[L_ACdBr₂]a square pyramidal geometry.[L_BCdBr₂]has two Cd-containing structures per unit cell, whereby one Cd center adopted a distorted tetrahedral geometry and the other exhibited square bipyramidal geometry. Thein situ-generated alkyl derivatives of the synthesized complexes were assessed in the ring-opening polymerization ofrac-lactide. Heterotactic polylactides (PLAs) were furnished with all complexes. The[L_BZnCl₂]/MeLisystem produced PLA with a superior heterotactic bias (P_rup to 0.94) at −25 °C. PLAs with wide-ranging polydispersity indices (1.16-2.23) and low molecular weights were produced in all cases, irrespective of the specific M(II) center and ancillary ligand utilized.