Nucleophilic Silylenoid Character of Stable Phosphonium Sila–ylides

Abstract

Stabilising the core: Contrary to the case of non‐stabilised transient silylenes, which react with carbonyl compounds to form donor–acceptor adducts, the reaction of a phosphine‐coordinated silylene with an aldehyde proceeds by a concerted [2+1] cycloaddition with a very low energy barrier to afford a pentacoordinate oxasilirane (see scheme). This result clearly demonstrates the behaviour of phosphonium sila–ylides as nucleophilic silylenoids.

Nachweis des Lewis‐amphoteren Charakters von Tris(pentafluorethyl)silanid, [Si(C2F5)3]−

“…1 b weist die Geometrie einer stark verzerrten quadratischen Pyramide ( τ =0.18 im nicht fehlgeordneten Anion und τ =0.12 im fehlgeordneten Anion) [31] mit einem C 2 F 5 ‐Substituenten in Apex‐Position auf (Abbildung 3). Das Strukturmotiv eines dreigliedrigen Si‐O‐C‐Heterocyclus ist bereits aus der Side‐on‐Addition von Silylenen an Carbonylverbindungen bekannt [26–28] . Die Si1‐O1‐ und die C26‐O1‐Bindung im Dreiring von 1 b sind mit den Bindungen von bereits bekannten fünffach‐ und vierfach‐koordinierten Oxasiliranen vergleichbar.…”

Synthesis and Characterization of an Isolable Base‐Stabilized Silacycloprop‐1‐ylidene

“…In contrast to the phosphine-stabilized silylene 1, which shows a silylene-like reactivity, [16,19,25] 3 does not react with olefins or alkynes. However, it readily reacts with the Lewis acid BH 3 ·THF to give the corresponding borane complex 4, which was isolated as colorless crystals in 93 % yield.…”

Diastereoselective Synthesis of Bulky, Strongly Nucleophilic, and Configurationally Stable P-Stereogenic Tricyclic Phosphines

“…The isomerization of hypervalent silirene 2 would involve the P-Si bond dissociation and a rotation around the Si-N bond axis in the resulting silirene 6. 10 The molecular structure of 3b indicates that the P-C1 bond (1.796 Å) is substantially shorter than the single P-C4 bond (1.873 Å), suggesting a strong π-electron donation of the enamine function. Therefore, an enhanced nucleophilic character of phosphines 3 was expected, and in order to evaluate their donor ability the Rh(I) and Ir(I) dicarbonyl complexes 9 and 10 were prepared by reaction of 3a,b with [RhCl(CO) 2 ] 2 and [IrClCOD] 2 respectively.…”