Isolable Anion Radical of Blue Disilene (^tBu₂MeSi)₂SiSi(SiMe^tBu₂)₂ Formed upon One-Electron Reduction:  Synthesis and Characterization

Abstract

The highly twisted tetrakis(di-tert-butylmethylsilyl)disilene 4 was prepared and reacted with (t)BuLi in THF, producing disilene anion radical 5 upon one-electron reduction. The anion radical 5 was isolated in the form of its lithium salt as extremely air- and moisture-sensitive red crystals. The molecular structure of 5 was established by X-ray crystallography, which showed a nearly orthogonal structure (twisting angle of 88 degrees ) along the central Si-Si bond, with a length of 2.341(5) A, which is 3.6% elongated relative to that of 4. The interesting feature of 5 is that one of the central Si atoms has radical character, whereas the other Si atom has silyl anion character. An electron spin resonance (ESR) study of the hyperfine coupling constants of the (29)Si nuclei indicates that rapid spin exchange occurs between these central Si atoms on the ESR time scale.

The Versatile Chemistry of Disilenides: Disila Analogues of Vinyl Anions as Synthons in Low-valent Silicon Chemistry

“…23,24 As can easily be rationalized by qualitative orbital overlap arguments the ³³* separation must decrease with increasing deviation from planarity. Larger angles ª and¸necessarily result in a narrower HOMOLUMO gap and thus a red shift in the longest wavelength UVvis absorption.…”

“…The blue color of tetrasilyldisilene 8 (Chart 2, max = 612 nm), for instance, has been attributed to the large twisting angle of¸= 54.5°, which is due to the steric repulsion of the bulky substituents (R = SiMe t Bu 2 ). 24 The coordination environments of both silicon atoms are almost planar (sum of bond angles 359.7 and 359.6°) due to the presumably relatively small singlettriplet gap of the bis(silyl)silylene fragments constituting the double bond. In two isomeric cyclic disilenes, the additional ring strain in trans-9 imposes stronger distortions from planarity compared to an almost planar cis-9 (cis-9:¸= 3.9°, ª = 3.9 and 12.4°; trans-9: = 42.5°, ª = 32.9 and 30.9°).…”

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

“…The tin homologue of the above-mentioned compound, distannene anion radical 19, was also synthesized by Sekiguchi et al, using the same synthetic protocol, that is, the direct reduction of the precursor distannene (tBu 2 MeSi) 2 -Sn=Sn(SiMetBu 2 ) 2 (20) with potassium mirror in THF in the presence of [2.2.2]cryptand (Scheme 14). [37] The crystal structure of 19 is reminiscent of that of the silicon analogue 17: [36] a highly twisted (74 o ) Sn-Sn skeleton with a bond length of 2.8978(3) Å, which is 0.2295 Å longer than that in the starting distannene 20 because of the decrease in bond order upon one-electron reduction ( Figure 11). As in the case of 17 mentioned above, the geometry around the two Sn atoms is different: one of them is essentially planar (355.4°), whereas the other one is highly pyramidal (323.2°), again assuming that the negative charge and the unpaired electron are effectively separated between the two Sn atoms.…”

Ein molekularer Siliciumcluster mit einem “nackten” Gerüstatom

“…[11] Andererseits sollten die unlängst beschriebenen Disilenide, Analoga von Vinylanionen, gute Ausgangsverbindungen für mehrfach ungesättigte p-Systeme von Silicium sein, die sich ihrerseits wegen der Labilität der Si = Si-Bindungen leicht zu den anvisierten, teilsubstituierten Clustern umlagern sollten. [17] Um die Natur der Wechselwirkungen aufzuklären, die zu den extremen Verzerrungen in 3 führen, wurden DFTRechnungen auf B3LYP/6-31G(d,p)-Niveau am H-substituierten Grundkörper 3 u durchgeführt. [18] Bemerkenswerterweise ist 3 u nur ein Übergangszustand der Ringinversion des potenziell bishomoaromatischen Isomers, in dem beide Siliciumbrücken auf derselben Seite des zentralen Dreirings zu liegen kommen.…”