Abstract
1-Trimethylsilyl, 1-R (R = Me, Et, i-Bu)-2,3,4,5-tetraphenyl-1-silacyclopentadiene [Ph4C4Si(SiMe3)R] are synthesized from the reaction of 1-trimethylsilyl,1-lithio-2,3,4,5-tetraphenyl-1-silacyclopentadienide anion [Ph4C4SiMe3]−•[Li]+ (3) with methyl iodide, ethyl iodide, and i-butyl bromide. The versatile intermediate 3 is prepared by hemisilylation of the silole dianion [Ph4C4Si]−2•2[Li]+ (2) with trimethylsilyl chloride and characterized by 1H-, 13C-, and 29Si-NMR spectroscopy. 1,1-bis(R)-2,3,4,5-tetraphenyl-1-silacyclopentadiene [Ph4C4SiR2] {R = n-Bu (7); t-Bu (8)} are synthesized from the reaction of 2 with n-butyl bromide and t-butyl bromide. Reduction of 7 and 8 with lithium under sonication gives the respective 3-silolenide 2,5-carbodianions {[Ph4C4Si(n-Bu)2]−2•2[Li]+ (10) and [Ph4C4Si(t-Bu)2]−2•2[Li]+ (11)}, which are characterized by 1H-, 13C-, and 29Si-NMR spectroscopy. Polarization of phenyl groups in 3 is compared with those of silole anion/dianion, germole anion/dianion, and 3-silolenide 2,5-carbodianions 10 and 11.
Highlights
Cyclopentadienyl anion, the most representative aromatic compound, has for a long time played important roles in organic and organometallic chemistry [1,2,3]
Molecules 2013, 18 to synthesize the analogue framework [4,5,6,7], in which one of carbon atoms is replaced by a heavier group 14 atom, and the ultimate question is to find out how its aromaticity changes and is maintained [8,9,10,11,12,13,14,15]
1-methyl-2,3,4,5-tetraphenyl-1-silacyclopentadienide anion was synthesized and crystallized in THF as a [2+2] dimer of its Si = C bond in aromatic ring structures [39], the dimer of which is dissociated to the original silole anions when it is reacted with alkyl halides or trimethylchlorosilane in THF [40]
Summary
Cyclopentadienyl anion, the most representative aromatic compound, has for a long time played important roles in organic and organometallic chemistry [1,2,3]. There are several routes for silole syntheses, via 1,4-dilithio-butadienides by using diphenylacetylene [16,17,49] and 1,4-dihalobutadienes [23,50,51], the intramolecular reductive cyclization of diethynylsilanes [52,53], metallacyclic transfer reactions [54], and organoboration [55,56,57,58] Those synthetic methods are not applicable to synthesizing of various siloles derivatives at the Si atom, especially for preparing 1-trimethylsilyl group substituted siloles due to the feasibility of the nucleophilic attack on the Si-Si bond by carbanions [22,24,27,59,60] and silole anion [39].
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