Isolable Silyl and Germyl Radicals Lacking Conjugation with π-Bonds:  Synthesis, Characterization, and Reactivity

Abstract

The one-electron oxidation reaction of 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 first isolable radical 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 planar geometry around the radical centers. The ESR spectra of 1 and 2 showed strong signals with characteristic satellites due to the coupling with the 29Si and 73Ge nuclei. The small values of the hyperfine coupling constants a(29Si) and a(73Ge) clearly indicate the pi-character of both radicals, corresponding to a planar geometry and sp2 hybridization of the radical centers. Both 1 and 2 easily undergo halogenation reactions with carbon tetrachloride, 1,2-dibromoethane, and benzyl bromide to form the corresponding halosilanes and halogermanes.

Si‐, Ge‐, and Sn‐Centered Free Radicals: From Phantom Species toGrams‐Order‐Scale Materials

“…Its crystal structure was isomorphous to that of 7: an absolutely planar configuration of the Ge center with the same in-plane and clockwise arrangement of the methyl groups. [20] The EPR spectrum of 8 displayed a strong central signal (g-factor = 2.0229) with the very characteristic picture of ten satellite signals with the hfcc a( 73 Ge) = 2.00 mT (Figure 6). Again, one should recognize that Ge radical 8 is a planar π radical, parallel to the above case of silyl radical 7.…”

“…The corresponding Ge analogue (tBu 2 MeSi) 3 Ge · (8) was prepared in a similar, and even simpler, procedure: by the direct reaction of tBu 2 MeSiNa with GeCl 2 ·dioxane in Et 2 O (Scheme 6). [20] At first, the intermediate germylene (tBu 2 -MeSi) 2 Ge: was generated in situ, followed by the formation of the germylsodium derivative (tBu 2 MeSi) 3 GeNa, and its subsequent oxidation with a second equivalent of GeCl 2 ·dioxane. It is worth mentioning that in the above reactions the GeCl 2 ·dioxane complex behaved as a very mild and selective oxidizing reagent, whose high oxidizing ability was documented in the previous electrochemical studies [E 1/2 (red) = -0.41 V].…”

(Me3Si)3SiH: Twenty Years After Its Discovery as a Radical‐Based Reducing Agent

“…The radicals (Et 3 Si) 3 SiC, (iPr 3 Si) 3 SiC, (tBuMe 2 Si) 3 SiC and (tBu 2 MeSi) 3 SiC have the practically planar structure 41, due to the steric repulsions among the bulky silyl substituents. [51,52] Hydrosilylation using (Me 3 Si) 3 SiH or silicon surfaces: The radical-based hydrosilylation of carbon-carbon or carbonoxygen double bonds by (Me 3 Si) 3 SiH is an important class of reactions. The initially generated (Me 3 Si) 3 SiC radical adds to the double bond to give a radical adduct, which then reacts with (Me 3 Si) 3 SiH to give the addition product, together with "fresh" (Me 3 Si) 3 SiC radicals to perpetuate the chain.…”

Stable Cubic Phosphorus‐Containing Radicals

“…Examples of stable neutral radicals are less common, but several have been structurally characterized recently in the solid state by X-ray crystallography, for example, CB 11 Me 12 C, [3] [M(dbdab) 2 ] (M = Al, Ga; dbdab = 1,4-di-tertbutyl-1,4-diazabutadiene), [4] [R 2 MMR]C (M = Ga, Al; R = SitBu 3 ), [5][6][7] R 3 SiSi(tBu) 2 C [R = SiMe(tBu) 2 ], [8] [R 3 E]C (E = Si, Ge; R = SiMe(tBu) 2 ), [9] and [Ge(C 6 H 3 Mes 2 -2,6)]C (Mes = 2,4,6-(CH 3 ) 3 C 6 H 2 ). [10] The structure of the phosphorus-centered radical DP[CH(SiMe 3 ) 2 ] 2 C has been determined in the gas phase by electron diffraction.…”