Carboxylation of terminal alkynes with CO2 catalyzed by bis(amidate) rare-earth metal amides

Abstract

Three novel bis(amidate) rare-earth metal amides {LRE[N(SiMe₃)₂]·THF}₂ (H₂L = N,N′-(cyclohexane-1,2-diyl)bis(4-tert-butylbenzamide); RE = La(1), Nd(2), Y(3)), which were prepared by the treatment of the bridged amide proligand H₂L with RE[N(SiMe₃)₂]₃ in tetrahydrofuran, have been characterized by single-crystal X-ray diffraction, elemental analyses, and NMR for complexes 1 and 3. All the complexes were found, for the first time, to be efficient catalysts for the direct carboxylation of terminal alkynes with CO₂ at ambient pressure. And the Nd-based catalyst 2 showed the highest reactivity. Various propiolic acids with a good functional group tolerance were successfully synthesized in high-to-excellent yields under mild conditions.