Synthesis of Silaketenimine Anion and Its Coupling with Isocyanide

Herein, we describe the first synthesis of anionic silaketenimines
and the coupling product with an isocyanide. Treatment of boryl silanorcaradienyllithium
[CH2(L)­N]2BSiLi (where L = B­[N­(Ar)­CH]2 and Ar = 2,6-iPr2C6H3) with isocyanides afforded silaketenimine anions [CH2(R)­N]2BSi­(Li)CNR featuring a SiCN
allenic structure. X-ray diffraction studies and density functional
theory calculations strongly support the presence of an anionic silicon
atom and a strong π bond between the silicon and carbon atoms.
One of the silaketenimine anions underwent a formal [2 + 2] cycloaddition
reaction with a second molecule of isocyanide to give a novel silacyclopropyl
anion with a delocalized anionic skeleton. These reactions
demonstrated that the bonding nature of the boryl lithiosilylene was
distinct from that of common silylenes.