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

Homoleptic ceric pyrazolates (pz) Ce(RR'pz) (R = R' = Bu; R = R' = Ph; R = Bu, R' = Me) were synthesized by the protonolysis reaction of Ce[N(SiHMe)] with the corresponding pyrazole derivative. The resulting complexes were investigated in their reactivity toward CO, revealing a significant influence of the bulkiness of the substituents on the pyrazolato ligands. The efficiency of the CO insertion was found to increase in the order of Bupz < Phpz < BuMepz < Mepz. For comparison, the pyrrole-based ate complexes [Ce(pyr)(-pyr)(thf)][Li(thf)] (pyr = pyrrolato) and [Ce(cbz)(thf)][Li(thf)] (cbz = carbazolato) were obtained via protonolysis of the cerous ate complex Ce[N(SiHMe)]Li(thf) with pyrrole and carbazole, respectively. Treatment of the pyrrolate/carbazolate complexes with CO seemed promising, but any reversibility could not be observed.