Alexandra TSYBIZOVA
ETH de Zurich Mardi 28 novembre 2023
à 14h
Sorbonne Université
Campus Pierre et Marie Curie
Tour 32-42, salle 101
« Mechanistic investigation of Cu-mediated C-H carboxylation using CO2 »
The mechanism of a model, Cu-mediated direct heterocyclic C-H carboxylation reaction was investigated using in operando monitoring mass spectrometry. An optimized pressurized sample infusion setup allowed for the detection and gas-phase characterization of on-pathway reactive intermediate to carboxylation. Qualitative collision-induced dissociation measurements allowed the comparison of different heterocyclic substrates to their propensity towards carboxylation: 6- aminobenzoxazole, benzoxazole, 1H-benzimidazole, and benzothiazole. C2-carboxylates of 1H- benzimidazole and benzothiazole showed similar and larger barriers to decarboxylation compared to 6-aminobenzoxazole-C2-carboxylate. This trend was ratified by complementary DFT calculations investigating concerted and stepwise barriers to carboxylation for the studied heterocycles. However, the relative barriers to carboxylation in the gas phase did not compare to observed solution-phase reactivities. Previous studies suggested that the higher pKa of benzothiazole prevented C-H activation to proceed. However, in this work, we established that benzothiazole can be deprotonated under reaction conditions. Therefore, the inability of the model reaction to carboxylate such substrates is likely to arise from solution-phase effects, such as outer-sphere interactions with the base or Lewis-acidic counterions.
Contact IPCM :
Héloïse Dossmann