Silicon(i) chemistry: the NHC-stabilised silicon(i) halides Si₂X₂(Idipp)₂ (X = Br, I) and the disilicon(i)-iodido cation [Si₂(I)(Idipp)₂].

ABSTRACT: An efficient method for the synthesis of the NHC-stabilised Si(i) halides Si₂X₂(Idipp)₂ (2-X, X = Cl, Br, I; Idipp = C[N(C₆H₃-2,6-iPr₂)CH]₂) was developed, which involves the oxidation of Si₂(Idipp)₂ (1) with 1,2-dihaloethanes. Halogenation of 1 is a diastereoselective reaction leading exclusively to a racemic mixture of the RR and SS enantiomers of 2-X. Compounds 2-Br and 2-I 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 2-Br and 2-I in solution, which involved a hindered rotation of the NHC groups about the Si-C_NHC bonds. Iodide abstraction from 2-I by [Li(Et₂O)_2.5][B(C₆F₅)₄] selectively afforded the disilicon(i) salt [Si₂(I)(Idipp)₂][B(C₆F₅)₄] (3). X-ray crystallography and variable-temperature NMR spectroscopy of 3 in combination with quantum chemical calculations shed light on the ground-state geometric and electronic structure of the [Si₂(I)(Idipp)₂]⁺ ion, which features a Si[double bond, length as m-dash]Si bond between a trigonal planar coordinated Si^II atom with a Si-I bond and a two-coordinate Si⁰ center carrying a lone pair of electrons. The dynamics of the [Si₂(I)(Idipp)₂]⁺ ion were studied in solution by variable-temperature NMR spectroscopy and they involve a topomerisation, which proceeds according to quantum theory via a disilaiodonium intermediate ("?-bonded" isomer) and exchanges the two heterotopic Si sites.

SUBMITTER: Arz MI 

PROVIDER: S-EPMC6054044 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature