Synthesis of 2,6‐Diarylphenyldimethylsilyl Cations: Polar‐π Distribution of Cation Character

CF Activation of Fluorobenzene by Silylium Carboranes: Evidence for Incipient Phenyl Cation Reactivity

“…[21] An extreme fluorophilicity was found for silylium carborane [2][CHB 11 Cl 11 ]. [22] Fluoride transfer from fluorobenzene to silicon takes place within hours at room temperature to give silanes 4 and 5 (Scheme 2). Several unidentified minor by-products were observed as well, probably because equimolar amounts of highly reactive, Brønsted-acidic Wheland intermediates are formed.…”

Synthesis and Crystal Structure of a Silyl‐Stabilized Allyl Cation Formed by Disruption of an Arene by a Protonation–Hydrosilylation Sequence

“…[9] Would such an arenium species such as the toluenium ion (CH 3 Table 2). Carbon atoms C19, C20, and C21 resonate at 225, 129, and 197 ppm, respectively.…”

“…[2] Recent investigations focused on the conversion of silane 1 into the silylium ion 2 + , which is stabilized by Si-p interactions (Scheme 1). [3] A side path of these studies led to the isolation of a crystalline bicyclic allylic cation 3 + that is formed with concomitant disruption of an aromatic ring. Invited or not, the solid-state structure of 3 + teaches us much about this important class of organic intermediates and suggests an intricate stereochemistry, which reveals a likely mechanism for this unexpected transformation.…”

“…To that same end, treatment of terphenylsilane 1 with the trityl salt [Ph 3 C][CHB 11 Me 5 Br 6 ] afforded, in addition to the intended silylium carborane 2[CHB 11 Me 5 Br 6 ], a small amount of a second compound, as indicated by NMR spectroscopy. [3] Attempts to crystallize pure 2[CHB 11 Me 5 Br 6 ] from ortho-dichlorobenzene/hexane yielded instead yellow prisms of the minor product 3[CHB 11 Me 5 Br 6 ] (Scheme 1), the identity of which was determined by X-ray crystallography (Figure 1). [4] The crystal structure of 3[CHB 11 Me 5 Br 6 ] consists of wellseparated cations and anions, and 3 + can be described as a silabicyclo [3.3.1]nonenyl cation with the formal positive charge distributed over a five-atom unit Si-C18-C19-C20-C21.…”

Ein gezähmtes Silyliumion für Diels‐Alder‐Reaktionen bei niedrigen Temperaturen

“…[1,2] Das Vorhandensein eines Elektronensextetts am Siliciumatom macht entsprechende Elektronenmangelverbindungen zu potenten Lewis-Säuren -so stark, dass selbst schwache, eigentlich unreaktive Lewis-Basen (Lösungsmittelmoleküle) koordinieren. [3] Sowohl die sterische Abschirmung des leeren Orbitals am Siliciumatom [4,5] als auch das raffinierte Design schwach koordinierender Anionen [6,7] ermöglichten die Strukturaufklärung eines Silyliumions. [8] Können nun derartige reaktive Zwischenstufen von Nutzen für die Synthesechemie sein?…”