Highly Active Homoleptic Zinc and Magnesium Complexes Supported by Constrained Reduced Schiff Base Ligands for the Ring-Opening Polymerization of Lactide

Abstract

New homoleptic zinc and magnesium complexes containing constrained reduced Schiff base ligands based on substituted 7-hydroxy-1-indanone were successfully synthesized and used as a catalyst for the polymerization of lactide. The ligands contain a side arm having different basicity because dimethylamino, pyridyl, and furfuryl groups are shown to greatly affect the polymerization rates. The homoleptic zinc complex containing constrained reduced Schiff base ligands and a dimethylamino side arm was highly active, giving a 92% conversion of l-lactide in 3 min using [LA]:[Zn]:[BnOH] = 500:1:2 at room temperature. The polymerization is pseudo-first-order dependent on the LA concentration. Well-controlled and living behavior of the zinc complex was observed and demonstrated in the preparation of stereodiblock and triblock copolymers of l -, d-, and rac-lactide in a one-pot sequential synthesis with a predictable block length, block sequence, and narrow dispersity rapidly in 10 min. Stereocomplex formation was observed for PLA made sequentially from 100 l-LA, 100 rac-LA, and 100 d-LA having a high T m of up to 220 °C.

Synthesis and Characterization of Zinc(II), Cadmium(II), and Palladium(II) Complexes with the Thiophene-Derived Schiff Base Ligand

“…Frequently, it involves application of an alkoxide metal-derived catalyst or other species that can generate an alkoxide in-situ . − The choice of the ligands determines the catalytic behavior of central metals in the complexes. The main goal of the study is to develop a promising catalyst to promote ROP reactions using Schiff base metal complexes as an effective ROP of lactide (LA) for controllable polymerization and to achieve polymers with narrow-molecular-weight distributions. ,− In the current study, the preliminary polymerization data revealed that the in situ -generated [L TH ZnCl 2 ]/[LiO i Pr] system resulted in high polymerization activity with heterotactic enchainment in the resultant poly­(lactic acid)­s (PLAs) compared to its Cd­(II) and Pd­(II) complexes.…”

Synthesis of Benzoxazine Functionalized Amine‐Bridged Bis(phenolato) Rare Earth Complexes and Their Application in Ring‐Opening Polymerization of rac‐Lactide

“…Stereoregular PLAs are crystalline polymers with a high melting point, whereas atactic PLA is amorphous and brittle. Therefore, extensive efforts have been focused on the synthesis of stereoregular PLAs, [ 4‐5 ] and a variety of catalysts/initiators have been applied in the controlled ROP of rac ‐LA, including organocatalysts, [ 6‐8 ] main group metal, [ 9‐17 ] transition metal, [ 18‐20 ] and rare earth metal complexes. [ 21‐23 ] Among them, rare earth metal complexes have attracted intensive attention due to their high activity, high stereoselectivity, and good controllability for polymerization under mild conditions.…”

Zinc 8-aminotrihydroquinolines appended with pendant N-diphenylphosphinoethyl arms as exceptionally active catalysts for the ROP of ε-CL

“…While zinc catalysts bound by tridentate ligands have been central to developments in this area, there were also many reports concerned with zinc complexes bearing bidentate N^N ( 12–20 , Chart 1) 32–37 or N^O ( 21–25 , Chart 1) 38 ligands, which are in most cases formed as dimeric species. 32 For example, N^N-containing 12–16 bearing N-heterocyclic donors can efficiently catalyze the ROP of ε-CL and LA, 8 a ,33,34 while those containing sterically encumbered pyridylamido ligands ( 14 ) can mediate the formation of stereodiblock poly(LLA- b -DLA). 34 b Bisguanidines have also proved attractive due to the stability of their zinc complexes for the ROP of cyclic esters under industrially relevant conditions.…”