Reaction of silyl substituted dichlorosilanes with lithiosilanes in hexane leads exclusively to the corresponding stable silyl radicals. Two radicals, the new (t-Bu2MeSi)(2)HSi(t-Bu2MeSi)(2)Si center dot (1) and the previously isolated (t-Bu2MeSi)(3)Si center dot (2), were isolated and fully characterized including by X-ray crystallography. This one-step method is general and was applied for the synthesis of other silyl. radicals. Upon irradiation radical 1 (yellow solution in hexane) decays to yield the corresponding disproportionation products, silane and disilene (blue colored). In contrast, radical 2 is photostable in the absence of additives, but it abstracts hydrogen from triethylsilane and 2-propanol upon irradiation. DFT calculations and irradiation experiments with lambda > 400 nm suggest that SOMO-1 square SOMO excitation, which provides better electron accepting properties to the radical, is responsible for the photoreactivity of 1 and 2.
One-electron oxidation of a stable tris[di-tert-butyl(methyl)silyl]silyl radical by the triphenylmethylium ion produces the corresponding silylium ion 2. However, this underwent a rapid intramolecular methyl group migration to form a more stable silylium ion 4 via a Wagner–Meerwein type rearrangement. The facile 1,3-methyl migration over the three peripheral silicon atoms in 4 was observed in NMR time scale.
Nearly Planar Nonsolvated Monomeric Silyl- and Germyllithiums as a Result of an Intramolecular CH−Li Agostic Interaction
作者:Masaaki Nakamoto、Tomohide Fukawa、Vladimir Ya. Lee、Akira Sekiguchi
DOI:10.1021/ja021142r
日期:2002.12.1
Pale-yellow crystals of the nonsolvated monomeric silyl- and germyllithiums, tris[di-tert-butyl(methyl)silyl]silyllithium 2a and tris[di-tert-butyl(methyl)silyl]germyllithium 2b, were obtained by one-electron reduction of the corresponding silyl and germyl radicals with lithium in hexane. The crystal structure analysis of both 2a and 2b showed almost planar geometry around the anionic centers, due to both intramolecular CH-Li agostic interactions and steric reasons. However, the free anions [(tBu2MeSi)3Si-][Li+(THF)4] 3a and [(tBu2MeSi)3Ge-][Li+(THF)n] (n = 3, 4) 3b no longer showed a planar geometry, because of the absence of the intramolecular CH-Li agostic interaction. A temperature-dependent 1H NMR study of 2a showed that the CH-Li interaction is weak.
Isolable Silyl and Germyl Radicals Lacking Conjugation with π-Bonds: Synthesis, Characterization, and Reactivity
作者:Akira Sekiguchi、Tomohide Fukawa、Masaaki Nakamoto、Vladimir Ya. Lee、Masaaki Ichinohe
DOI:10.1021/ja0126780
日期:2002.8.1
tris[di-tert-butyl(methyl)silyl]silyl and -germyl anions with dichlorogermylene-dioxane complex results in the formation of stable tris[di-tert-butyl(methyl)silyl]silyl and -germyl radicals 1 and 2, representing the firstisolableradical species of heavier Group 14 elements lacking stabilization by conjugation with pi-bonds. The crystal structures of both silyl and germyl radicals 1 and 2 showed a completely
Reaction of silyl substituted dichlorosilanes with lithiosilanes in hexane leads exclusively to the corresponding stable silyl radicals. Two radicals, the new (t-Bu2MeSi)(2)HSi(t-Bu2MeSi)(2)Si center dot (1) and the previously isolated (t-Bu2MeSi)(3)Si center dot (2), were isolated and fully characterized including by X-ray crystallography. This one-step method is general and was applied for the synthesis of other silyl. radicals. Upon irradiation radical 1 (yellow solution in hexane) decays to yield the corresponding disproportionation products, silane and disilene (blue colored). In contrast, radical 2 is photostable in the absence of additives, but it abstracts hydrogen from triethylsilane and 2-propanol upon irradiation. DFT calculations and irradiation experiments with lambda > 400 nm suggest that SOMO-1 square SOMO excitation, which provides better electron accepting properties to the radical, is responsible for the photoreactivity of 1 and 2.