Silicon(i) Chemistry: the NHC-stabilised Silicon(i) Halides SiX(Idipp) (X = Br, I) and the Disilicon(i)-iodido Cation [Si(I)(Idipp)]

An efficient method for the synthesis of the NHC-stabilised Si(i) halides SiX(Idipp) (, X = Cl, Br, I; Idipp = C[N(CH-2,6-Pr)CH]) was developed, which involves the oxidation of Si(Idipp) () with 1,2-dihaloethanes. Halogenation of is a diastereoselective reaction leading exclusively to a racemic mixture of the and enantiomers of . Compounds and were characterised by single-crystal X-ray crystallography and multinuclear NMR spectroscopy, and their electronic structures were analysed by quantum chemical methods. Dynamic NMR spectroscopy unraveled a fluxional process of and in solution, which involved a hindered rotation of the NHC groups about the Si-C bonds. Iodide abstraction from by [Li(EtO)][B(CF)] selectively afforded the disilicon(i) salt [Si(I)(Idipp)][B(CF)] (). X-ray crystallography and variable-temperature NMR spectroscopy of in combination with quantum chemical calculations shed light on the ground-state geometric and electronic structure of the [Si(I)(Idipp)] ion, which features a Si[double bond, length as m-dash]Si bond between a trigonal planar coordinated Si atom with a Si-I bond and a two-coordinate Si center carrying a lone pair of electrons. The dynamics of the [Si(I)(Idipp)] ion were studied in solution by variable-temperature NMR spectroscopy and they involve a topomerisation, which proceeds according to quantum theory a disilaiodonium intermediate ("π-bonded" isomer) and exchanges the two heterotopic Si sites.