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.