Abstract
Homoleptic ceric pyrazolates (pz) Ce(RR’pz)4 (R = R’ = tBu; R = R’ = Ph; R = tBu, R’ = Me) were synthesized by the protonolysis reaction of Ce[N(SiHMe2)2]4 with the corresponding pyrazole derivative. The resulting complexes were investigated in their reactivity toward CO2, revealing a significant influence of the bulkiness of the substituents on the pyrazolato ligands. The efficiency of the CO2 insertion was found to increase in the order of tBu2pz < Ph2pz < tBuMepz < Me2pz. For comparison, the pyrrole-based ate complexes [Ce2(pyr)6(µ-pyr)2(thf)2][Li(thf)4]2 (pyr = pyrrolato) and [Ce(cbz)4(thf)2][Li(thf)4] (cbz = carbazolato) were obtained via protonolysis of the cerous ate complex Ce[N(SiHMe2)2]4Li(thf) with pyrrole and carbazole, respectively. Treatment of the pyrrolate/carbazolate complexes with CO2 seemed promising, but any reversibility could not be observed.
Highlights
Cerium Pyrazolates and Pyrrolates onRare-earth–metal complexes are capable of efficiently activating carbonylic compounds including carbon dioxide [1,2,3,4,5,6]
Various rare-earth-metal-basedcatalysts are known to promote the catalytic cycloaddition of carbon dioxide and epoxide-producing cyclic carbonates, which in case of propylene carbonate, can be used as electrolyte solvent in lithium-ion batteries [30,31,32,33,34,35,36,37]
We have recently described the application of homoleptic ceric pyrazolate [Ce(Me2 pz)4 ]2 in the catalytic cycloaddition of carbon dioxide and epoxides as well as the reversible capture of CO2 [38,39]
Summary
Cerium Pyrazolates and Pyrrolates onRare-earth–metal complexes are capable of efficiently activating carbonylic compounds including carbon dioxide [1,2,3,4,5,6]. This can be realized by capturing and storing carbon dioxide with tailor-made surface-reactive materials [12,13,14,15,16]. Rare-earth metals have successfully been studied as catalysts for the copolymerization of carbon dioxide and epoxides to yield polycarbonates [24,25,26,27,28,29,30]. Various rare-earth-metal-based (pre)catalysts are known to promote the catalytic cycloaddition of carbon dioxide and epoxide-producing cyclic carbonates, which in case of propylene carbonate, can be used as electrolyte solvent in lithium-ion batteries [30,31,32,33,34,35,36,37]
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