Imidazolidene Carboxylate Bound MBPh₄ Complexes (M = Li, Na) and Their Relevance in Transcarboxylation Reactions

Abstract

Combination of 1,3-bis(2,6-diisopropylphenyl)imidazolum-2-carboxylate (IPrCO(2)) with the Lewis acids MBPh(4), where M = Li or Na, provided two separate complexes. The crystal structures of these complexes revealed that coordination to NaBPh(4) yielded a dimeric species, yet coordination of IPrCO(2) with LiBPh(4) yielded a monomeric species. Combination of 1,3-bis(2,4,6-trimethylphenyl)imidazolum-2-carboxylate (IMesCO(2)) with LiBPh(4) also afforded a dimeric species that was similar in global structure to that of the IPrCO(2)+NaBPh(4) dimer. In all three cases, the cation of the organic salt was coordinated to the oxyanion of the zwitterionic carboxylate. Thermogravimetric analysis of the crystals demonstrated that decarboxylation occurred at lower temperatures than the decarboxylation temperature of the parent NHC·CO(2) (NHC = N-heterocyclic carbene). Kinetic analysis of the transcarboxylation of IPrCO(2) to acetophenone with NaBPh(4) to yield sodium benzoylacetate was performed. First-order dependences were observed for IPrCO(2) and acetophenone, whereas zero -order dependence was observed for NaBPh(4). Direct dicarboxylation was observed when I(t)BuCO(2) was added to MeCN in the absence of added MBPh(4).

Organic reactions for the electrochemical and photochemical production of chemical fuels from CO2 – The reduction chemistry of carboxylic acids and derivatives as bent CO2 surrogates

“…Louie and coworkers have now shown that the strength of binding CO 2 to the NHC fragment is tunable in a series of decarboxylation and transcarboxylation studies [33,34]. Thermal stability studies have yielded a series of data shown in Fig.…”

Direct Carboxylation of C(sp3)-H and C(sp2)-H Bonds with CO2 by Transition-Metal-Catalyzed and Base-Mediated Reactions

“…Catalysts 2017, 7, 380 22 of 54 1,3-diaryl-imidazolium-2-carboxylates (78) have been used as CO2-transfer agents for the carboxylation of ketones and nitriles [66,106,111,112]. Reactions in which a "C-COO − " moiety behave as CO2-transfer agent towards an organic compound are not common.…”

“…Carboxylated products are isolated in the form of metal salts in yield ranging from 60 to 81%. More recently Louie has undertaken a detailed mechanistic study on the abovementioned trans-carboxylation reaction by using IPr-CO2 (78), IMes-CO2 and I t But-CO2 as CO2-carriers [112]. Investigating the role played by the alkali metal, Louie succeeded in isolating NHC-CO2 .…”

“…M (M = Li + , Na + ) adducts (79,80) that were characterized by single crystal X-ray diffraction analysis. More recently Louie has undertaken a detailed mechanistic study on the abovementioned trans-carboxylation reaction by using IPr-CO 2 (78), IMes-CO 2 and I t But-CO 2 as CO 2 -carriers [112]. Investigating the role played by the alkali metal, Louie succeeded in isolating NHC-CO 2 ·M (M = Li + , Na + ) adducts (79,80) that were characterized by single crystal X-ray diffraction analysis.…”

Recent advances in neutral and anionic N-heterocyclic carbene – betaine interconversions. Synthesis, characterization, and applications

“…of acetophenone to form benzoyl acetate, or methanol to form monomethyl carbonate. [94][95][96] 1,3-Di-tert-butylimidazolium-2-carboxylate was used as recyclable organocatalyst in the cycloaddition of aziridines and carbon dioxide. 97 Imidazolium-2-thiocarboxylates were also described as organocatalysts.…”