Cyclic (Alkenyl)(Amino)Carbene (SMeCAenAC): Introducing a Member to the Cyclic (Alkyl)(Amino)Carbenes Family Featuring a Narrow Energy Gap

Herein, we report the carbene-like activity of a nonisolable, highly ambiphilic cyclic (alkenyl)(amino)carbene (^SMeCA_enAC, 3), which is stabilized as [(^SMeCA_enAC)(H)N(SiMe₃)₂] (4). This protected form (4) is stable in air and moisture. Compound 4 can be used as a carbene source through deamination upon heating to 130–140 °C. Moreover, density functional theory (DFT) calculations indicate that ^SMeCA_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 (3) can be synthesized on a multigram scale with a good yield. Moreover, the ^SMeCA_enAC-coordinated copper complex showed excellent efficiency in the catalytic addition of phenols to electron-deficient olefins. This study also highlights that [^SMeCA_enAC-H]OTf can be used for metal-free catalysis, a property uniquely characteristic of an ambiphilic carbene, even though the formation of free ^SMeCA_enAC (3) was not achieved.