Synthesis of Silylium and Germylium Ions by a Substituent Exchange Reaction

Abstract

The reaction of diarylalkylsilanes and -germanes with trityl cation in the presence of a weakly coordinating anion to give the corresponding triarylsilylium or -germylium ions was investigated. This reaction provides a facile access to a larger range of these sterically highly hindered Lewis acids. The factors that promote the substituent exchange were studied, and significant effects of the substituent, of the solvent, and of the group 14 element were revealed. A combined solid-state XRD and NMR investigation of the tris(pentamethylphenyl) silylium borate [(Me5C6)3Si]2[B12Cl12] disclosed the trigonal planar coordination environment of the silicon atom in this silylium ion. NMR investigations indicate for 2,4,6-triisopropylphenyl-substituted silylium and germylium ions the onset of C–H···E+ three-center interactions (E = Si, Ge) between the distant CH bond of the isopropyl group and the positively charged group 14 element atom.

On Silylated Oxonium and Sulfonium Ions and Their Interaction with Weakly Coordinating Borate Anions

“…As displayed in Scheme3,b oth formation reactions of 9 are exergonic with À31.2 and À19.3 kcal mol À1 in the gas phase (0.0 and 4.2 kcal mol À1 in toluene, Ta ble S8, S9), theoretically manifesting the thermodynamically possible formationo f9 in this dynamic equilibriumc hemistry.S imilar exchange reactions have been observedb yM üller and co-workers [21,62] and Oestreich et al, [63] who described substituent scrambling in the formation of the arene silylium cation [(Mes) 3 4 Si in benzene or toluene indicating substituent redistribution, too. As displayed in Scheme3,b oth formation reactions of 9 are exergonic with À31.2 and À19.3 kcal mol À1 in the gas phase (0.0 and 4.2 kcal mol À1 in toluene, Ta ble S8, S9), theoretically manifesting the thermodynamically possible formationo f9 in this dynamic equilibriumc hemistry.S imilar exchange reactions have been observedb yM üller and co-workers [21,62] and Oestreich et al, [63] who described substituent scrambling in the formation of the arene silylium cation [(Mes) 3 4 Si in benzene or toluene indicating substituent redistribution, too.…”

“…[1][2][3] Classicalh ydrogen onium specieso fa ll three groups (H 4 E + with E = N, P, As, and Sb; [4,5] H 3 E + with E = O, S; [4,[6][7][8] H 2 E + with E = F, Cl) [9,10] were already reported. Ever since the pioneering silyliumi on work by the groups of Lambert, Reed, Oestreich, and Müller, [17][18][19][20][21] salts bearingh omoleptict rimethylsilyl substituted cations ([T 4 E] + with E = N, [22] P, and As; [23] [T 2 E] + with E = F-I [12] and T = Me 3 Si)h aveb een in the focus of main group chemistry,h owever,t here is hardly anythingk nown about persilylated chalconium ions of the type [T 3 E] + . Ever since the pioneering silyliumi on work by the groups of Lambert, Reed, Oestreich, and Müller, [17][18][19][20][21] salts bearingh omoleptict rimethylsilyl substituted cations ([T 4 E] + with E = N, [22] P, and As; [23] [T 2 E] + with E = F-I [12] and T = Me 3 Si)h aveb een in the focus of main group chemistry,h owever,t here is hardly anythingk nown about persilylated chalconium ions of the type [T 3 E] + .…”

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

“…[97,229] It was not until 2002 that the first true silylium ion [(Mes) 3 Si] [HCB 11 Me 5 Br 6 ]w as structurally characterized. [346,347] In addition, the ion-like compounds Me 3 Si[RCB 11 F 11 ](R= H, Et) with an excellent fluorinated WCA are rather close to being ionic, with the sum of the angles at the silicon center being about 3578 8.T hey even show electrical conductivity in the melt at 90 8 8C. The weak coordination from the WCA in conjunction with the kinetic stabilization of the silicon center imparted by the sterically demanding mesityl substituents enabled characterization of this true silylium ion.…”

Der Einsatz von N‐heterocyclischen Vinylliganden zur Isolierung stabiler Divinylgermylene und eines Germylium‐Kations

“…[19] Die Methylgruppe,d ie an das Ge-Zentrum in 8 gebunden ist, resoniert bei À1.06 ppm ( 1 HNMR;C 6 D 6 ), was im Vergleich zu dem Kation [Trip 2 GeMe] + (Trip = 2,4,6-Me 3 C 6 H 2 )( 1.53 ppm;C 6 D 6 )d eutlich abgeschirmt ist [20] und auf eine mçgliche Stabilisierung der positiven Ladung am Ge durch zusätzliche C-Ge-p-Wechselwirkungen hindeutet. Vong rçßerem Interesse war jedoch die Reaktion von 5a mit MeOTf, die ein orangefarbenes Produkt ergab,d as später als das dreifach koordinierte Germylium-Salz [(IPrCH) 2 GeMe]OTf (8,Schema 4) charakterisiert wurde.Wie zu erwarten, lieferte 8 symmetrische IPr = CH À -Umgebungen (auf der Basis von 1 H-und 13 C{ 1 H}-NMR-Daten)und eine 19 F-NMR-Resonanz bei À78.9 ppm in CD 2 Cl 2 ,d ie freiem OTf À zugeordnet wurde.…”

“…[20,21] Die Ge-C vinyl -Abstände sind annähernd äquivalent (Ge1-C8 1.815(4), Ge1-C4 1.820(4) ), wohingegen ein grçßerer Ge-C Me -Abstand (Ge1-C9) von 1.926(4) beobachtet wird. [20,21] Die Ge-C vinyl -Abstände sind annähernd äquivalent (Ge1-C8 1.815(4), Ge1-C4 1.820(4) ), wohingegen ein grçßerer Ge-C Me -Abstand (Ge1-C9) von 1.926(4) beobachtet wird.…”