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 [Formula: see text] skeleton. These reactions demonstrated that the bonding nature of the boryl lithiosilylene was distinct from that of common silylenes.