Tricyanomethane or Dicyanoketenimine ‐ Silylation makes the Difference

Pseudohalides such as tricyanomethanide, [C(CN) 3 ] − , are well known in chemistry, biochemistry and industrial chemistry. The protonated species HC(CN) 3 , a classic hydrogen pseudohalide Brønsted acid, is a very strong acid with a p K a value of −5. However, HC(CN) 3 is difficult to handle as it tends to decompose rapidly or, more precisely, to oligo‐ and polymerize. Therefore, silylated pseudohalide compounds with the [Me 3 Si] + as the “big organometallic proton” have become interesting, exhibiting similar chemical properties but better kinetic protection. Here, the stepwise silylation of the pseudohalide anion [C(CN) 3 ] − is reported, forming the heavier homologue of HC(CN) 3 , namely [Me 3 Si][C(CN) 3 ], and in presence of two additional [Me 3 Si] + cations even the dicationic species [(Me 3 Si−NC) 3 C] 2+ as stable [B(C 6 F 5 ) 4 ] − salt. Surprisingly, in contrast to the protonated species HC(CN) 3 , in which the proton is bound to the central carbon atom of [C(CN) 3 ] − , silylation of the [C(CN) 3 ] − anion occurs at one of the three terminal nitrogen atoms, thus forming the long‐sought dicyanoketenimine [Me 3 Si−NC−C(CN) 2 ]. All further silylation steps take place exclusively on the terminal N atoms of the three CN groups and not on the central carbon atom, until the intriguing, highly symmetrical dication, [(Me 3 Si−NC) 3 C] 2+ , is finally generated. The experimental data are supported by quantum chemical calculations in terms of thermodynamics and chemical bonding.