Synthesis and Characterization of Silylated Phosphonium [P(OSiMe₃)₄]⁺ and Phosphate [O₂P(OSiMe₃)₂]⁻ Salts

Abstract

Starting from an optimized synthesis of silylated phosphoric acid, OP(OSiMe), a borate salt bearing the [P(OSiMe)] cation was generated in the reaction of OP(OSiMe) with [MeSi-H-SiMe][B(CF)], isolated, and fully characterized. Analogously to the protonated species, phosphoric acid (HPO) reaction of OP(OSiMe) with a base led to the formation of the unknown [OP(OSiMe)] anion, which could be crystallized as potassium salt and structurally characterized, too. Both [P(OSiMe)] and [OP(OSiMe)] can be regarded as the formal autoprotolysis products of OP(OSiMe).

Easy Access to Enantiomerically Pure Heterocyclic Silicon‐Chiral Phosphonium Cations and the Matched/Mismatched Case of Dihydrogen Release

“…( rac )‐ 1 was synthesized by reaction of t BuPhHSiCl with LiCH 2 P(S)( t Bu) 2 (see the Supporting Information). Hydride abstraction from ( rac )‐ 1 , assisted by intramolecular attack of the P=S group at the silicon atom, was achieved using B(C 6 F 5 ) 3 , which was Lewis acidic enough for irreversible formation of the S ‐silylated phosphonium hydroborate ( rac )‐ 2 a (Scheme 1, route a ) [24] . As an alternative, we opened up a route toward ion pair ( rac )‐ 2 b (with [B(C 6 F 5 ) 4 ] − as counteranion) through Brønsted acid‐promoted dehydrogenation, [25] and we were fortunate to be able to isolate and crystallize a protonated intermediate [( rac )‐ 3 ] before the release of dihydrogen at 150 °C under neat conditions (Scheme 1, route b ).…”

Silylierte Schwefelsäure: Herstellung eines Tris(trimethylsilyl)oxosulfonium[(Me3Si‐O)3SO]+‐Salzes

“…Interessanterweise wurde zwar die Chemie von T 3 PO 4 und seiner silylierten kationischen Spezies [T 4 PO 4 ] + erforscht, [37][38][39] aber über ein silyliertes Kation des Typs [T 3 SO 4 ] + wurde unseres Wissens bisher nichts berichtet. Allerdings wurde protonierte Schwefelsäure, [H 3 SO 4 ] + , von Minkwitz et al in einem supersauren System (HF/SbF 5 ) als [SbF 6 ] À -Salz isoliert.…”

Silylated Sulfuric Acid: Preparation of a Tris(trimethylsilyl)oxosulfonium [(Me3Si−O)3SO]+ Salt

“…It is known that carborates are much more chemically robust compared to the [B(C 6 F 5 ) 4 ] À anion. [4,12,51] Indeed, when [13] 35.6 [T 4 PO 4 ] + , [37] and computed 385 ppm for naked [Me 3 Si] + (g) , [52,53] see SI, Table S3). As the 29 Si NMR chemical shifts can be used as an indicator for the silylium ion character (and the deviation from planarity, see below), [52][53][54] that is, for the strength of the [Me 3 Si] + interaction with the solvent T 2 SO 4 , it can be assumed that T 2 SO 4 is a rather strong coordinating solvent utilizing the scale by Cremer et al (À50 to 90 ppm, cf.…”

“…[4,6] Like the protonated species, all these silylated cations should be regarded as strong Lewis acids that can be utilized as T + transfer reagents. Interestingly, while the chemistry of T 3 PO 4 and its silylated cationic species [T 4 PO 4 ] + has been explored, [37][38][39] nothing has been reported about a silylated cation of the type [T 3 SO 4 ] + to the best of our knowledge. However, protonated sulfuric acid, [H 3 SO 4 ] + , was isolated by Minkwitz et al in a super acidic system (HF/SbF 5 ) as [SbF 6 ] À salt.…”