Synthesis, structures, and catalytic efficiency in ring opening polymerization of -lactide with tridentate bidentate cobalt(ii), zinc(ii), and cadmium(ii) complexes containing -substituted ,-bis((3,5-dimethyl-1-pyrazol-1-yl)methyl)amine ligands.

A series of Co(ii), Zn(ii), and Cd(ii) complexes supported by 1-(3,5-dimethyl-1-pyrazol-1-yl)--((3,5-dimethyl-1-pyrazol-1-yl)methyl)--(furan-2-ylmethyl)methanamine (L) and ,-bis((3,5-dimethyl-1-pyrazol-1-yl)methyl)-4-isopropylaniline (L) were synthesized. The direct chelation of CoCl·6HO, ZnCl, and CdBr·4HO by the ligands produced [LMX] (L = L or L; M = Zn or Co, with X = Cl; M = Cd, with X = Br) complexes in high yields. Structural studies revealed that [LCoCl] and [LZnCl] adopted distorted tetrahedral geometries, as L coordinated the metal centers in a bidentate fashion, while L coordinated the metal centers in a tridentate fashion through the nitrogen atoms of the pyrazole and amine moieties, so that [LCoCl] and [LZnCl] exhibited trigonal bipyramidal geometries and [LCdBr] a square pyramidal geometry. [LCdBr] has two Cd-containing structures per unit cell, whereby one Cd center adopted a distorted tetrahedral geometry and the other exhibited square bipyramidal geometry. The generated alkyl derivatives of the synthesized complexes were assessed in the ring-opening polymerization of lactide. Heterotactic polylactides (PLAs) were furnished with all complexes. The [LZnCl]/MeLi system produced PLA with a superior heterotactic bias ( up 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.