Carbon Dioxide/Epoxide Coupling Reactions Utilizing Lewis Base Adducts of Zinc Halides as Catalysts. Cyclic Carbonate versus Polycarbonate Production

Abstract

The reactions of zinc halides with 2,6-di-methoxypyridine or 3-trifluoromethylpyridine in dichloromethane have led to the formation of quite different complexes. Specifically, reactions involving pyridine containing electron donating methoxy substitutents have provided salts of the type [Zn(2,6-dimethoxypyridine)4][Zn2X6], as revealed by elemental analysis and X-ray crystallography. On the other hand, simple bis-pyridine adducts of zinc halides were isolated from the reactions involving the pyridine ligand with electron withdrawing substituents and characterized by X-ray crystallography, for example, Zn(3-trifluoromethylpyridine)2Br2. These zinc complexes were shown to be catalytically active for the coupling of carbon dioxide and epoxides to provide high molecular weight polycarbonates and cyclic carbonates, with the order of reactivity being Cl > or = Br > I, and 2,6-di-methoxypyridine > 3-trifluoromethylpyridine. Polycarbonate production from carbon dioxide and cyclohexene oxide was shown to be first-order in both metal precursor complex and cyclohexene oxide, as monitored by in situ infrared spectroscopy at 80 degrees C and 55 bar pressure. For reactions carried out in CO2 swollen epoxide solutions in the absence of added quantities of pyridine, the copolymer produced contained significant polyether linkages. Alternatively, reactions performed in the presence of excess pyridine or in hydrocarbon solvent, although slower in rate, afforded completely alternating copolymers. For comparative purposes, zinc chloride was a very effective homopolymerization catalyst for polyethers. Additionally, zinc chloride afforded copolymers with 60% carbonate linkages in the presence of high carbon dioxide pressures. In the case of cyclohexene oxide, the copolymer back-biting reaction led exclusively to the production of the trans cyclic carbonate as shown by infrared spectroscopy in v(C=O) region and X-ray crystallography. The unique feature of these catalyst systems is their simplicity.

Novel ternary block copolymerization of carbon dioxide with cyclohexene oxide and propylene oxide using zinc complex catalyst

“…This means that large amount of CHO homopolymerized instead of copolymerized with CO 2 . This is similar with the case that the homoolymerization of CHO easily takes place using the catalyst systems of zinc complexes [32][33][34]. Figure 5 shows the relationship of the ratio of propylene carbonate unit to cyclohexene carbonate unit and the feed molar ratio of epoxide monomers.…”

Copolymerization of CO2 and epoxides mediated by zinc organyls

“…24,25 Since this pioneering work many catalysts have been developed for the copolymerization of CO 2 with epoxides. [13][14][15][16][17][18] Especially zinc based catalyst systems were shown to be efficient. A variety of initiating systems based on different zinc species alone 26,27 as well as in combination with additives e.g.…”

Zinc Complexes of Piperazinyl‐Derived Aminephenolate Ligands: Synthesis, Characterization and Ring–Opening Polymerization Activity

“…[29,30,[52][53][54][55] Therefore, studies were performed using 6 and 7/ROH in combination with DMAP and Bu 4 NBr as cocatalysts, Table 4, towards the reaction of CO 2 with cyclohexene oxide. A control reaction was performed using Bu 4 NBr alone, as ionic salts such as this are known to catalyze the formation of cyclic carbonates (Table 4, entry 1).…”