Synthesis of a Counteranion‐Stabilized Bis(silylium) Ion

Abstract

The preparation of a molecule with two alkyl‐tethered silylium‐ion sites from the corresponding bis(hydrosilanes) by two‐fold hydride abstraction is reported. The length of the conformationally flexible alkyl bridge is crucial as otherwise the hydride abstraction stops at the stage of a cyclic bissilylated hydronium ion. With an ethylene tether, the open form of the hydronium‐ion intermediate is energetically accessible and engages in another hydride abstraction. The resulting bis(silylium) ion has been NMR spectroscopically and structurally characterized. Related systems based on rigid naphthalen‐n,m‐diyl platforms can only be converted into the dications when the positively charged silylium‐ion units are remote from each other (1,8 versus 1,5 and 2,6).

Silylium Ions: From Elusive Reactive Intermediates to Potent Catalysts

“…196 Employing [HCB 11 Cl 11 ] − as the counteranion, the group of Oestreich recently accomplished the synthesis of a bis(silylium) ion (Scheme 26). 197 Key to success for 2-fold hydride abstraction was the installation of a conformationally flexible ethylene bridge that allows to energetically access the open form of the otherwise stable hydronium ion intermediate. As shown in the molecular structure of bis(silylium) ion 90 (Figure 12), the two cationic silicon centers adopt an anti conformation, likely to minimize electrostatic and steric repulsions.…”

“…The syntheses of several cyclic hydronium ions using the Corey reaction have been reported (see Table 10), and their spectroscopic and crystallographic characterization established that these cations are well-separated from the counteranion and solvent molecules. 114,144,164,178,[182][183][184][185][186]197 Historically, the first silyl cation identified to have such an intramolecular 3c2e bond was the cyclic cation 63a + introduced by Muller. 182 While the corresponding borate salt 63a[B(C 6 F 5 ) 4 ] is only marginally stable at room temperature, the naphthalene-based bissilylhydronium ions 21a + and its mixed Si/Ge variant 100 + are stable even in boiling toluene.…”

Synthesis of Norbornene-Based Phosphine-Stabilized Silylium Ions Behaving as Masked Frustrated Lewis Pairs

“…The study of these species has been facilitated by the use of a Lewis base that can intramolecularly interact with the silylium center, to afford a good balance between reactivity and stability ( II , Figure ). Following this strategy, several different types of donor groups have been introduced to achieve this intramolecular stabilization ( III – VI , Figure ).…”

Hydrogen‐Bridged Oligosilanylsilyl Mono‐ and Oligosilanylsilyl Dications

“…[14] Recently, the Oestreich group succeeded in taming bissilylium ions 5-7 (Figure 1) by using halogenated carborate anions as external stabilizing donors, starting from either spatially well separated bishydridosilanes (for dications 5 and 6) or small cyclic SiÀ HÀ Si bridged cations (in the case of 7). [30] In the present work, we describe the results of our systematic study on a series of intramolecularly stabilized silyl cations, all featuring one or two six-membered cationic [Si 5 H] + rings. This includes the persila-variant 8 of cation 1, the interaction of the cationic SiÀ HÀ Si bridge with additional SiÀ H functionalities in the branched oligosilanylsilyl cation 9 and its transformation to dication 10 as an example for a bissilyl Lewis acid that is stabilized only by silane/silylium interaction (Figure 2).…”