Anionic N ‐Heterocyclic Carbene‐Based Silicon Halides with a Four‐Coordinated Silicon Atom

Silicon(IV) halides [{(Et 3 B)anIPr}SiHCl 2 ] ( 4 ) and [{(Et 3 B)anIPr}SiBr 3 ] ( 5 ) based on an anionic N ‐heterocyclic carbene (NHC) ligand (i.e., {(Et 3 B)anIPr} = (Et 3 B)C=C(H){N(Dipp)} 2 C, Dip p = 2,6‐ i Pr 2 C 6 H 3 ) are reported as crystalline solids. Compounds 4 and 5 featuring a four‐coordinated Si(IV) atom are prepared by reacting [Li{(Et 3 B)anIPr}] ( 3 ) with HSiCl 3 and SiBr 4 , respectively. 4 and 5 are characterized by spectroscopic and X‐ray diffraction methods. Density functional theory (DFT) calculations have been performed to elucidate the electronic structures as well as the fluoride ion affinities (FIAs) of 4 and 5 . The calculated FIA, a measure of Lewis acidity, of 4 and 5 is about 46 or 55 kJ/mol larger than that of HSiCl 3 and SiBr 4 , respectively.