Quantum Chemical Insights of Mesoionic <i>N</i> -Heterocyclic Olefin-Catalyzed <i>S</i> -Formylation of Thiols Using CO ₂

The activation and conversion of CO2 to value-added products are challenging chemical reactions in modern-day chemistry. Recently, we reported the S-formylation of thiols using CO2 as a C1 source, employing mesoionic N-heterocyclic olefin (mNHO) as a metal-free catalyst. This study uses a detailed density functional theory (DFT)-based investigation to explain the reaction mechanism of mNHO-catalyzed metal-free S-formylation of thiol under ambient conditions. DFT calculations provide a closer look at the CO2 activation process. It is observed that the formation of silyl formate is slightly favorable through the mNHO-silane adduct over the mNHO-CO2 adduct although both pathawys are thermodynamically feasible. Further, when mNHO is replaced by N-heterocyclic olefin (NHO), it unravels how the activation energy barrier changes, thus making a significant impact on the outcome of the catalytic reaction.