Metal and Ligand-Substituent Effects in the Immortal Polymerization of rac-Lactide with Li, Na, and K Phenoxo-imine Complexes

Abstract

A series of lithium, sodium, and potassium complexes with phenoxo-imine ligands M[(O-2-(RNCH)C6H4] [R = C6H5; 2- t BuC6H5; 2,6- i Pr2C6H3] and [O-2-(RNCH)-4,6- t Bu2C6H4] [R = C6H5; 2- t BuC6H5; 2,6- i Pr2C6H3] 1–3(a–f) have been synthesized. The molecular structures in the solid state of some of these complexes have been determined by X-ray diffraction. These compounds show different nuclearities and geometries around the metal center depending on the nature and the pocket of the ligand substituents. Of particular interest is the structure of compound 3e, being the first example of a potassium cubane complex obtained with this kind of ligand. The structural behavior in solution has also been studied by diffusion-ordered NMR spectroscopy (DOSY), showing a direct correlation between aggregation behavior and polymerization activity. Compounds 1–3(a–f) are extremely active catalysts in the ring-opening polymerization (ROP) of rac-lactide, achieving conversions of 100% in less than 1 min and heterorich-PLA that is modified by the metal atom and the ligand substituents. BnOH was used as co-initiator, and the presence of large amounts of the alcohol produces the immortal polymerization of rac-lactide in a more controlled process. Stoichiometric reactions involving the catalysts, BnOH, and lactide demonstrated an activated monomer mechanism for the polymerization of rac-lactide.

Stable Fe(iii) phenoxyimines as selective and robust CO2/epoxide coupling catalysts

“…Accordingly, all three ligands were synthesised in excellent yields (95-99%) via the straightforward condensation of methyl amine and mono-substituted salicylaldehydes (Scheme 2). 28 Confirming the synthesis of L1, L2 and L3, no aldehyde resonances were present in the 1 H NMR spectra, and diagnostic imine resonances were observed (CDCl 3 solvent, L1, δ = 8.33; L2, δ = 8.35; L3, δ = 8.30). Complexes C1-C3 were synthesised through deprotonation of pro-ligands L1-L3 using NaH (1.1 eq.)…”

The Facile Synthesis of Lithium 2‐R‐Hydroquinolinide Complexes and Their High Activity toward ROP of ε‐Caprolactone

“…Based on the aforementioned results obtained by the GPC, kinetic studies, NMR and MALDI‐TOF, it can be proposed that the ROP of ε ‐CL might be proceeding via coordination‐insertion mechanism , , . As shown in Scheme , in the absence of BnOH, the polymerization process involved: i) a weak coordination of ε ‐CL to lithium center to form an intermediate, ii) insertion of the monomer into the Li–N bond by nucleophilic attack, iii) propagation and ring‐closing termination to produce the cyclic polymers.…”

Synthesis and Application of Bimetallic Zinc(II) Phenoxy-Imine Complexes as Initiators for Production of Lactide Polymers

“…L1 and L2 were synthesized in high yields according to a modified literature procedure. [14][15][16][17]22 Complexes C1 and C2 ( Figure 1) were also obtained in high yields. The structures of these ligands allow the coordination of two zinc(II) centers while the vast majority of the phenoxy-imine ligands coordinate to only one metal.…”