Singlet carbenes as mimics for transition metals: synthesis of an air stable organic mixed valence compound [M-2(C-2)(+center dot); M = cyclic(alkyl)(amino)carbene]

A cyclic C-bromo-iminium bromide reacts with lithium trimethylsilyl acetylide to afford the title compound 2(+center dot) in 40% yield. In contrast to other organic mixed valence compounds, this radical cation can be stored in air. Oxidation and reduction of 2(+center dot) afford the corresponding dication 2(++) and neutral cumulene 2, respectively, in good yields.