Cyclic (Alkenyl)(Amino)Carbene(^<i>SMe</i>CA_enAC): Introducing aMember to the Cyclic (Alkyl)(Amino)CarbenesFamily Featuring a Narrow Energy Gap

Herein, we report the carbene-like activity of a nonisolable, highly ambiphilic cyclic (alkenyl)(amino)carbene (^<i>SMe</i>CA_enAC, <b>3</b>), which is stabilized as [(^<i>SMe</i>CA_enAC)(H)N(SiMe₃)₂] (<b>4</b>). This protected form (<b>4</b>) is stable in air and moisture. Compound <b>4</b> can be used as a carbene source through deamination upon heating to 130–140 °C. Moreover, density functional theory (DFT) calculations indicate that ^<i>SMe</i>CA_enAC has the smallest singlet–triplet gap (37.05 kcal/mol) and a narrow highest occupied molecule orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap (3.92 eV) among the cyclic (alkyl)(amino)carbenes (CAACs). The precursor of carbene (<b>3</b>) can be synthesized on a multigram scale with a good yield. Moreover, the ^<i>SMe</i>CA_enAC-coordinated copper complex showed excellent efficiency in the catalytic addition of phenols to electron-deficient olefins. This study also highlights that [^<i>SMe</i>CA_enAC-H]OTf can be used for metal-free catalysis, a property uniquely characteristic of an ambiphilic carbene, even though the formation of free ^<i>SMe</i>CA_enAC (<b>3</b>) was not achieved.