Dispersion-Energy-Driven Wagner–Meerwein Rearrangements in Oligosilanes

Abstract

The installation of structural complex oligosilanes from linear starting materials by Lewis acid induced skeletal rearrangement reactions was studied under stable ion conditions. The produced cations were fully characterized by multinuclear NMR spectroscopy at low temperature, and the reaction course was studied by substitution experiments. The results of density functional theory calculations indicate the decisive role of attractive dispersion forces between neighboring trimethylsilyl groups for product formation in these rearrangement reactions. These attractive dispersion interactions control the course of Wagner–Meerwein rearrangements in oligosilanes, in contrast to the classical rearrangement in hydrocarbon systems, which are dominated by electronic substituent effects such as resonance and hyperconjugation.

Catalytic diastereo- and enantioselective additions of versatile allyl groups to N–H ketimines

“…2c); these lower e.r. might partly arise from an increase in attractive London dispersion forces between the 3,5-bis-(2,4,6-( i -Pr) 3 -phenyl)phenyl group and the substrate’s alkyl chain 45,46,47 . It is however more plausible that higher conformational mobility of the alkyl chains disrupt N→Na chelation [less optimal C NHC -Cu-C 1 -C 2 dihedral angle in I (151.3°) vs. in I (131.8°)].…”

Selective One‐Pot Syntheses of Mixed Silicon‐Germanium Heteroadamantane Clusters

“…A further increase in the crystallization time caused an increasing contamination of the crystal crop by a third heteroadamantane, the Si 9 Ge 5 derivative [1] , in which only one of the six GeMe 2 vertices of [0] is exchanged for SiCl 2 . Marschner prepared sila‐adamantane [A] , the close molecular relative to [0] , [1] , and [2] , in a fundamentally different way by a reaction inspired by Schleyer's adamantane synthesis (8 steps from SiCl 4 and Me 3 SiLi, 17 % overall yield) [2,9] …”

“…[nBu 4 N]Cl using the in a fundamentally different way by a reaction inspired by Schleyer's adamantane synthesis (8 steps from SiCl 4 and Me 3 SiLi, 17 % overall yield). [2,9] How are the formations of dichlorosilylenes (SiCl 2 ) are extruded from the cluster cores and dimethylgermylenes (GeMe 2 ) are incorporated. Formal cyclocondensation of 6 SiCl 2 moieties would give perchlorinated cyclohexasilane, which was indeed detected by 29 Si NMR spectroscopy in the form of [cyclo-Si 6 Cl 12 • 2Cl] 2À .…”

“…Apart from Kouvetakis’ perhydrogenated single‐source Si x Ge y precursors, which have been successfully used for the CVD of corresponding mixed semiconductors,[ 5 , 6 ] only few examples of complex (polycyclic) Si x Ge y oligomers are known to‐date, making a systematic assessment of their properties difficult. [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ] In this regard, the neo ‐Si 3 Ge 2 structure [B] (Figure 1 b) is noteworthy, which was obtained by the du Mont group from Me 3 GeCl and HSiCl 3 /NEt 3 (Benkeser reagent). [ 15 , 16 ] The analogous reaction with Me 2 GeCl 2 led to the double silylation product Me 2 Ge(SiCl 3 ) 2 .…”

Spaltung nicht aktivierter Si‐C(sp3)‐Bindungen mit Reedschen Carboransäuren: Bildung bekannter und unbekannter Silyliumionen

“…Diese Vorgehensweise wäre eine Ergänzung der üblichen Herstellungsverfahren von Silyliumionen [11] durch entweder Hydridabstraktion von Hydrosilanen [12] oder den Ansatz über Allylabgangsgruppen bei sterisch gehinderten Systemen. [13] [15] Um die Allgemeingültigkeit der Methode hervorzuheben, unterwarfen wir repräsentative Trialkylsilane mit Abgangsgruppen, deren Labilitätgegenüber Protonen bekannt ist, der bewährten Reaktionsvorschrift (Tabelle 2). [16] Aktivierte Si-C(sp 3 )-Bindungen wie in Allyl- [2,17] und überraschenderweise Benzylsilanen [18] führten sauber zu den gegenanionstabilisierten Tr ialkylsilyliumionen (Nr.1-3).…”