Synthesis of a labile CAAC-based diazoalkene: formation of a C4-cumulene and a head-to-tail dimer

Abstract

Herein, we report the synthesis of a cyclic (alkyl)(amino)carbene (CAAC)-based diazoalkene from the reaction of NHC/CAAC-based carbodicarbene with nitrous oxide. In contrast to the previously reported mesoionic N-heterocyclic carbene (mNHC)- and N-heterocyclic carbene (NHC)-based analogues, this CAAC-based diazoalkene is kinetically labile at room temperature and undergoes gradual conversion to a C4-cumulene. The lability is potentially attributed to the stronger π-accepting character of the CAAC motif relative to that of the NHC. The formation of the CAAC-based diazoalkene is evidenced by its head-to-tail dimerization upon treatment with MeOH. This study reveals the profound difference in the influence of carbene motifs, NHC versus CAAC, on the stability of carbene-based diazoalkenes.