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(SiHMe(2))(2)](4) with the corresponding pyrazole derivative. The resulting complexes were investigated in their reactivity toward CO(2), revealing a significant influence of the bulkiness of the substituents on the pyrazolato ligands. The efficiency of the CO(2) 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)(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(SiHMe(2))(2)](4)Li(thf) with pyrrole and carbazole, respectively. Treatment of the pyrrolate/carbazolate complexes with CO(2) seemed promising, but any reversibility could not be observed.