Tricyanomethane or Dicyanoketenimine-Silylation makes the Difference.

Pseudohalides such as tricyanomethanide, [C(CN)], are well known in chemistry, biochemistry and industrial chemistry. The protonated species HC(CN), a classic hydrogen pseudohalide Brønsted acid, is a very strong acid with a pK value of -5. However, HC(CN) is difficult to handle as it tends to decompose rapidly or, more precisely, to oligo- and polymerize. Therefore, silylated pseudohalide compounds with the [MeSi] 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)] is reported, forming the heavier homologue of HC(CN), namely [MeSi][C(CN)], and in presence of two additional [MeSi] cations even the dicationic species [(MeSi-NC)C] as stable [B(CF)] salt. Surprisingly, in contrast to the protonated species HC(CN), in which the proton is bound to the central carbon atom of [C(CN)], silylation of the [C(CN)] anion occurs at one of the three terminal nitrogen atoms, thus forming the long-sought dicyanoketenimine [MeSi-NC-C(CN)]. 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, [(MeSi-NC)C], is finally generated. The experimental data are supported by quantum chemical calculations in terms of thermodynamics and chemical bonding.