Stable Phosphonium Sila-ylide with Reactivity as a Sila-Wittig Reagent

Abstract

The silicon congeners of well-known phosphonium ylides have been considered only as short-lived reactive intermediates. We successfully synthesized a remarkably stable phosphonium sila-ylide. Its X-ray structure reveals a long Si-P bond and a strongly pyramidalized silicon center, indicating a very weak P-Si pi interaction. In addition, it exhibits an alpha,beta-ambiphilic character with a nucleophilic silicon center, similar to its carbon-congener phosphonium ylides. This property of the phosphonium sila-ylide allows its use as a sila-Wittig reagent with carbonyl derivatives.

Synthesis of a Stable Disilyne Bisphosphine Adduct and Its Non‐Metal‐Mediated CO2 Reduction to CO

“…Large silicon-phosphorus coupling constants have been observed for monophosphonium silaylides ( 1 J SiP = 141-157 Hz). [7] In the 31 P NMR spectrum, only one singlet at d = 34.7 ppm was detected in the typical region for phosphonium derivatives, which is downfield from that of starting trichlorosilane derivative 1 (d = 2.2 ppm). These data are in good agreement with a symmetrical arrangement of the molecule.…”

“…The silicon centers in 2 are less pyramidalized (AE8 Si = 3308) than that in monophosphonium ylide 3 (AE8 Si = 2998) [7] and even less than those in 4 with diketenimine character (AE8 Si = 3198). [11] To gain more insight into the properties of the molecule, DFT calculations were performed on the real compound 2.…”

“…[6] Thus, although phosphines are ubiquitous ligands in organometallic chemistry, their use in main-groupelement chemistry is not so frequent. Recently we reported that phosphine-stabilized silylenes (phosphonium silaylides) react either as sila-Wittig reagents [7] or as nucleophilic silylene complexes.…”

“…[7] By analogy, we now investigated the reduction of trichlorosilane derivative 1 using lithium (3 equiv) in THF at room temperature. The reaction readily affords the disilyne bisphosphine adduct 2, which can be isolated as red crystals (13 % yield).…”

Reversible Binding of Ethylene to Silylene–Phosphine Complexes at Room Temperature

“…Recently we described the synthesis of the first stable phosphonium sila-ylides 1 [16] with an enhanced silylenoid character. In particular, they react with carbonyl compounds in a barrier-free concerted [2+1] cycloaddition reaction.…”