Highly Active and Readily Accessible Proline‐Based Dizinc Catalyst for CO₂/Epoxide Copolymerization

Abstract

In the pursuit of CO -based materials, the development of efficient catalysts for the alternating copolymerization of CO and epoxides to give polycarbonates is receiving particular attention. Desirable attributes for such catalysts are high copolymerization activity at low CO pressure, as well as chemo- and stereocontrol over the formed polymer. Here, we report a novel chiral zinc catalyst that can be isolated in 97 % yield from commercial sources, and that produces polycarbonates selectively from neat cyclohexene oxide under 1 bar of CO pressure at temperatures above 50 °C. At 80 °C reaction temperature, TONs of 1684 and initial TOFs up to 149 h were measured, producing an isotactic-enriched polycarbonate with a probability P of 65 % for the formation of a meso diad. Insight into the dinuclear nature of the active species and the copolymerization progress has been gained from structural and spectroscopic studies.

Heterodinuclear zinc and magnesium catalysts for epoxide/CO2 ring opening copolymerizations

“…4 Illustration of the structures, activity and selectivity for some of the highest performing catalysts reported for CO 2 /CHO ROCOP. 22,25,33,34,59,61 a THF solution (Scheme 2b). 47 The structure shows the two different metals and has a molecule of THF coordinated at the Mg(II) centre.…”

Efficient Production of Poly(Cyclohexene Carbonate) via ROCOP of Cyclohexene Oxide and CO2 Mediated by NNO-Scorpionate Zinc Complexes

“…Thus, this new approach has led to the development of an interesting dinuclear thioalkoxide zinc scorpionate [Zn(bpzaepe) 2 {Zn(SAr) 2 }] (4) that behaves as an effective and selective initiator for poly(cyclohexene carbonate) production under milder conditions. Thus, catalyst 4 shows high catalytic activity (72% conversion and TOF up to 4.3 h −1 ), carbonate linkage (>99%) and polycarbonate selectivity (95%), at 70 • C, 10 bar of CO 2 pressure after 16 h, under solvent-free conditions, which constitutes a further step forward in the development of inexpensive, more efficient and non-toxic metal-based catalysts for the CO 2 fixation into the selective production of poly(cyclohexene carbonate) with narrow dispersities [17][18][19][20][21][22][23][24][25]51]. S1: Crystal data and structure refinement for 4, 5 and 6, Table S2: Effect of catalyst loading on the synthesis of poly(cyclohexene carbonate) catalysed by complex 4, Figure S5: GPC trace of poly(cyclohexene carbonate) produced by complex 4 at 70 • C and 10 bar CO 2 , Figure S6: Kinetic plot for ring-opening copolymerisation of cyclohexene oxide and carbon dioxide catalysed by complex 4 at 70 • C and 10 bar CO 2 , Figure S7: 1 H NMR and 13 C-{ 1 H} NMR spectra of poly(cyclohexene carbonate) sample prepared using complex 4 at 70 • C and 10 bar CO 2 .…”

“…Considering the current potential large-scale production of aliphatic polycarbonates by several companies [39][40][41], the employment of biocompatible metals such as zinc [42,43] is highly desirable to avoid potential health issues related to the toxicity of several metal-based residues in the isolated copolymers [44,45]. In particular, very active zinc-based catalysts in the absence of co-catalyst have been described [17][18][19][20][21][22][23][24][25] for polycarbonate production, some of them including alkoxide, amide, alkyl and acetate ligands as nucleophile in a coordination-insertion mechanism (see Chart 1).…”

“…Nevertheless, given the high thermodynamic stability and kinetic inertness of the CO 2 molecule [13], the environmental and economical viability of the ROCOP depends on the capability of the catalytic system to avoid high temperatures and pressures [14], which should be able, in turn, to operate at ambient temperatures and pressures [15] as well as controlling rates and polymer molecular weight and composition [16]. In this context, very active and selective metal-based catalysts have been successfully developed for the ROCOP of carbon dioxide and epoxides, frequently in the presence of a nucleophile as co-catalyst, with zinc [17][18][19][20][21][22][23][24][25], chromium [26,27], cobalt [28,29], iron [30,31], rare earth metals [32,33] and aluminum [34,35] as dominating metals in this field, although non-metal and organocatalyst systems have been also recently reported [36]. Similarly, very efficient bimetallic systems have been also reported for the selective copolymerization of epoxides and carbon dioxide, in which the epoxide is activated by one metal, while the attacking nucleophile is provided by the second centre [37,38].…”

Heterotrimetallic Carbon Dioxide Copolymerization and Switchable Catalysts: Sodium is the Key to High Activity and Unusual Selectivity

“…[27][28][29][30] Dinuclear metal complexes can be highly effective in CO 2 / epoxide ROCOP catalysis. [31][32][33][34] Theb est catalysts are highly active under low CO 2 pressures obviating the need of specialist reactors and operating without additives.C yclohexene oxide (CHO)/carbon dioxide ROCOP catalysis is an important benchmark and the product poly(cyclohexene carbonate) (PCHC) has an attractive high glass transition temperature,h igh Youngsm odulus and structural rigidity complementary to bio-based aliphatic polyesters.Sofar,none of the highly active metal catalysts can switch into CHO ringopening polymerization (ROP) and, therefore,itisdifficult to control the quantity and placement of CO 2 within the polymer chain. [35,36] To moderate these catalysts also requires better understanding of the polymerization mechanism, catalytic intermediate speciation, and factors mediating activity and selectivity.…”