Redox control of a polymerization catalyst by changing the oxidation state of the metal center

Abstract

The activity of cerium alkoxide complexes supported by a Schiff base ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The rate of L-lactide polymerization was modified by switching in situ between the cerium(III) and cerium(IV) species.

Reactivity and Properties of Metal Complexes Enabled by Flexible and Redox-Active Ligands with a Ferrocene Backbone

“…By taking advantage of the Ce(III)/Ce(IV) switch, we were also able to achieve a similar control of lactide polymerization directly at the metal site. 60 Recently, we applied this strategy to other electropositive metals including indium, 38 titanium, and zirconium. 43 In case of group 4 metals, by using (thiolfan)Zr(OtBu) 2 and (thiolfan*)Ti(OiPr) 2 as the reduced form of catalysts, we were able for the first time to achieve orthogonal reactivity through redox control of a remote site of the supporting ligand: the reduced form of the catalyst catalyzed lactide but not -caprolactone polymerization, while the opposite was true for the oxidized form of the catalyst.…”

“…[59][60][61]78 Due to the high acidity of the phenolic proton of H 2 (OEEO fc ), the installation of the metal fragment was facile; the choice of synthetic routes was mainly based on the desired composition of the pre-catalysts used for polymerization and the ease of availability of a metal precursor. Group 4 metal complexes supported by salfan, thiolfan, and thiolfan* ligands were prepared in a similar way using Zr(OtBu) 4 or Ti(OiPr) 4 as metal precursors.…”

“…43,[59][60][61] We first introduced a Schiff base derivative, salfen, to cerium and yttrium 78 and later developed the phosfen ligand that could be cleanly oxidized by a ferrocenium oxidant to enable redox controlled catalysis. 61 The salfan, thiolfan and thiolfan* ligands were found to fit group 4 metals well and have been exploited in redox-switchable copolymerization processes.…”

Computational Studies on the Selective Polymerization of Lactide Catalyzed by Bifunctional Yttrium NHC Catalyst

“…Theoretical calculations have shown their ability to efficiently describe and explain the ROP mechanism of cyclic esters, such as lactones and lactide at the molecular level [36][37][38][39][40][41]. For instance, Hormnirun et al conducted a DFT study on the rac-lactide ring-opening mechanism initiated by a series of bis(pyrrolidene) Schiff-base aluminium complexes to reveal the correlation between the structure of backbone linker and the polymerization activity and stereoselectivity [42].…”

Yttrium-Alkyl Complexes Supported by a Ferrocene-Based Phosphinimine Ligand

“…32 In addition to diamide ligands, we also explored the use of ferrocene-derived Schiff base metal complexes for the ring-opening polymerization of cyclic esters. 17,[33][34][35][36] Schiff base metal complexes have found numerous uses in coordination chemistry and catalysis, [37][38][39][40][41][42] alkoxide yttrium complexes supported by such ligands being intensely researched as initiators for the ring-opening polymerization of cyclic esters. 17,[35][36][43][44][45][46][47][48][49][50] On the other hand, reports of structurally characterized alkyl or aryl rare earth complexes bearing an imine functionality in the backbone are rare, [51][52] the majority being represented by phosphinimine ligands.…”