Block Copolymerization of Lactide and an Epoxide Facilitated by a Redox Switchable Iron‐Based Catalyst

Abstract

A cationic iron(III) complex was active for the polymerization of various epoxides, whereas the analogous neutral iron(II) complex was inactive. Cyclohexene oxide polymerization could be "switched off" upon in situ reduction of the iron(III) catalyst and "switched on" upon in situ oxidation, which is orthogonal to what was observed previously for lactide polymerization. Conducting copolymerization reactions in the presence of both monomers resulted in block copolymers whose identity can be controlled by the oxidation state of the catalyst: selective lactide polymerization was observed in the iron(II) oxidation state and selective epoxide polymerization was observed in the iron(III) oxidation state. Evidence for the formation of block copolymers was obtained from solubility differences, GPC, and DOSY-NMR studies.

Switching between Anion-Binding Catalysis and Aminocatalysis with a Rotaxane Dual-Function Catalyst

“…4 However, systems that can switch between different catalytic groups that promote different chemical transformations remain scarce. 5,6 We previously described 7 a rotaxanebased 8 switchable aminocatalyst 9 (1 'on' state/1-H + 'off' state) that modulates the rate of a range of organocatalyzed reactions via diverse activation pathways, 7b including iminium-ion, enamine and trienamine, and even tandem iminium-enamine processes (Figure 1). Here we show that the 'off' state of the aminocatalyst also corresponds to an 'on' state for anion-binding catalysis, 10 promoted by the presence of two triazolium groups on the rotaxane axle 11 that work together to bind anions 12,13 when the rotaxane macrocycle is located on the central ammonium group of the thread ( Figure 2).…”

Redox-Switchable Hydroelementation of a Cobalt Complex Supported by a Ferrocene-Based Ligand

“…An important goal of switchable catalysis is the demonstration of redox switches to be used for creating structural complexity by combining complementary on/off switches. 14,18,24 Despite the prevalence of hydroelementation chemistry, little if any research has been reported on switchable hydroelementation catalysts. Considering that the carboncarbon multiple bond is common to all hydroelementation substrates, reversibly switching the activity of a catalyst toward different reactions could provide a novel pathway to important chemicals.…”

A One‐Step Route to CO2‐Based Block Copolymers by Simultaneous ROCOP of CO2/Epoxides and RAFT Polymerization of Vinyl Monomers

“…Taking entry 3 for example, the theoretical MW of PPC and PMMA could be, respectively determined as 4.7 kg mol −1 and 7.3 kg mol −1 , while the M n (GPC) was 11.8 kg mol −1 . More direct evidence for the formation of PPC‐ b ‐PMMA came from the 1 H DOSY NMR spectra of the resultant products, where all signals shared the same diffusion coefficient (Supporting Information, Figure S47), while that of a blend of PPC/PMMA showed two different diffusion coefficients (Supporting Information, Figure S48) …”