Arz MI, Geiß D, Straßmann M, Schnakenburg G, Filippou AC. Silicon(i) chemistry: the NHC-stabilised silicon(i) halides Si
2X
2(Idipp)
2 (X = Br, I) and the disilicon(i)-iodido cation [Si
2(I)(Idipp)
2]
.
Chem Sci 2015;
6:6515-6524. [PMID:
30090270 PMCID:
PMC6054044 DOI:
10.1039/c5sc02681d]
[Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Accepted: 08/04/2015] [Indexed: 11/21/2022] Open
Abstract
An efficient method for the synthesis of the NHC-stabilised Si(i) halides Si2X2(Idipp)2 (2-X, X = Cl, Br, I) was developed, which involves the oxidation of Si2(Idipp)2 (1) with 1,2-dihaloethanes. Iodide abstraction from 2-I afforded the unprecedented silicon(i) salt [Si2(I)(Idipp)2][B(C6F5)4] (3).
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–CNHC 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
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Si bond between a trigonal planar coordinated SiII 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 (“π-bonded” isomer) and exchanges the two heterotopic Si sites.
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