Synthesis of a Bent 2‑Silaallene with a Perturbed Electronic Structure from a Cyclic Alkyl(amino) Carbene-Diiodosilylene

The cyclic alkyl­(amino) carbene (cAAC) 1 reacted with SiI4 in toluene, affording the cAAC-silicon tetraiodide complex [(cAACMe)­SiI4] (2, cAACMe = :C­(CH2)­(CMe2)2NAr, Ar = 2,6-iPr2C6H3). It further reacted with two equivalents of KC8 in toluene at room temperature to afford the first cAAC-diiodosilylene [(cAACMe)­SiI2] (3). DFT calculations show that the Ccarbene–Si bond in 3 is formed by the donation of the lone pair of electrons on the Ccarbene atom to the SiI2 moiety, while the π-back-bonding of the lone pair of electrons on the Si atom to the Ccarbene atom is negligible. The presence of the lone pair of electrons on the silicon atom in 3 is also evidenced by its reaction with N3SiMe3 to form the cAAC-silaimine complex [(cAACMe)­Si­(NSiMe3)­I2] (4). Compound 3 reacted with IiPrMe (:C­{N­(iPr)­CMe}2) in n-hexane to form the NHC-cAAC-silyliumylidene iodide [cAACMe(SiI)­IiPrMe]I (5), which was then reacted with two equivalents of KC8 in toluene to furnish [cAACMeSi­(IiPrMe)] (6). The experimental and theoretical studies suggest that 6 can be described as a bent silaallene with a perturbed electronic structure, which can be attributed to the different donor–acceptor properties of cAACMe and IiPrMe. Compounds 3–6 were elucidated by NMR spectroscopy, X-ray crystallography, and theoretical studies.