Effect of Substituents of Cerium Pyrazolates and Pyrrolates on Carbon Dioxide Activation

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 tBu(2)pz < Ph(2)pz < tBuMepz < Me(2)pz. For comparison, the pyrrole-based ate complexes [Ce-2(pyr)(6)(mu-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)](4)Li(thf) with pyrrole and carbazole, respectively. Treatment of the pyrrolate/carbazolate complexes with CO2 seemed promising, but any reversibility could not be observed.

Automated summary

In this study, homoleptic ceric pyrazolates with different substituents were synthesized, showing varied reactivity towards CO2 depending on the bulkiness of the substituents. Additionally, pyrrole and carbazole based ate complexes were obtained, but no reversibility was observed during the treatment with CO2.