Tuning the Thiolen: Al(III) and Fe(III) Thiolen Complexes for the Isoselective ROP of rac-Lactide

Abstract

A series of five iron and aluminum complexes bearing {ONSO} imine thiobis(phenolate) ligands have been prepared and applied to the ROP of rac-lactide. Fe(1)Cl produced PLA with a very strong isotactic bias (Pm = 0.79-0.89) and well-defined melting temperatures (Tm = 154-181 °C). The polymers have been characterized by a combination of 1 H{ 1 H} NMR, 13 C{ 1 H} NMR, GPC, TGA, DSC and pXRD. Fe(1)Cl has also been shown to activate CO2, at atmospheric pressure and concentrations, to form a carbonato bridged dimer. Fe(2-5)Cl and Al(1-5)Me were also active for lactide ROP demonstrating good molecular weight control 2 (Ð = 1.04-1.12) and moderate isotactic preference (Pm = 0.56-0.72), with polymerization outcome correlating with ligand substituents.

Zinc Complexes for PLA Formation and Chemical Recycling: Towards a Circular Economy

“…High‐molecular‐weight PLA is preferentially prepared from the cyclic dimer of lactic acid, lactide (LA), through ring‐opening polymerization (ROP) . Current PLA research seeks to reduce energy/material input of LA monomer synthesis, demonstrate and elucidate stereoselective initiation and prepare robust initiators to compete with Sn(Oct) 2 under industrial conditions …”

The synthesis, characterisation and application of iron(iii)–acetate complexes for cyclic carbonate formation and the polymerisation of lactide

“…21 Examples of Fe-mediated ROP in the literature are less prevalent despite the numerous benefits. [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Recently Duan et al synthesised and applied air-stable Fe(III)-salen-chloride complexes to the ROP of caprolactone and lactide. 12 Using propylene oxide (PO), as both the solvent and co-initiator, the postulated in situ generated Fe(III)-alkoxide species, formed via opening of PO by insertion of the Fe(III)-Cl bond, resulted in isotactic PLA (P m = 0.53-0.78) with broad dispersities (Đ = 1.…”

Salalen vs. thiolen: in the ring(-opening of epoxide and cyclic carbonate formation)

“…1). Although this geometry leans closer to a square-based pyramid compared with Fe(2) (t 5 = 0.78), bearing a chloride auxiliary group, 38,45 it is similar to the salalen complex, Fe(C), and the acetate auxiliary group analogue {Fe(C), t 5 = 0.66 and 'Fe(C)OAc', t 5 = 0.65}. 34,37 We have previously reported a carbonato-bridged dimer arising from the recrystallisation of Fe(2) in air and suggested that it could represent an intermediate in halide free CO 2 /epoxide coupling as reported by Muller and coworkers.…”

“…The Fe(III) chloride complexes bearing salalen [Fe(A-G)] and thiolen [Fe(1-5)] ligands [39][40][41][42][43][44] have been previously synthesised (Scheme 1), 37,38 and were screened for CO 2 /epoxide coupling with distilled CHO. Additionally, one Fe(III)-thiolen-acetate complex [Fe(6)] ( Fig.…”

“…21 We recently reported the synthesis of a range of Fe(III)salalen-chloride {ONNO} and Fe(III)-thiolen-chloride {ONSO} complexes and their application to the isoselective ring-opening polymerisation (ROP) of rac-lactide. 37,38 In particular, there are scarce examples of the 'thiolen', imine-thiobis(phenolate), family of ligands, 39,40 and they have not been applied to CO 2 / epoxide coupling despite the similarities to Della Monica's bis(thioether)-phenolate {OSSO} complexes.…”