The base-stabilized silacyclopropylidene 1 behaves as a versatile strongly nucleophilic ligand toward transition metals. The strong silylene-metal binding related to both increased σ-donating and π-accepting character of silylene 1 compared to N-heterocyclic carbenes (NHCs) allowed the synthesis of robust and air-stable silylene complexes. Of particular interest, the corresponding platinum(0) complex 6 exhibits high stability and a high level of selectivity and catalytic activity in hydrosilylation reactions that is superior to that of the related NHC-Pt(0) complexes.

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International audienceA stable base-stabilized sila-β-lactone was successfully synthesized and fully characterized. Interestingly, this sila-β-lactone shows a very unique reactivity toward ethanol, leading to the formation of an isolable donor/acceptor-stabilized silanoic acid

Oxidation of zero‐valent phosphine complexes [M(PtBu3)2] (M=Pd, Pt) has been investigated in 1,2‐difluorobenzene solution using cyclic voltammetry and subsequently using the ferrocenium cation as a chemical redox agent. In the case of palladium, a mononuclear paramagnetic PdI derivative was readily isolated from solution and fully characterized (EPR, X‐ray crystallography). While in situ electrochemical measurements are consistent with initial one‐electron oxidation, the heavier congener undergoes C−H bond cyclometalation and ultimately affords the 14 valence‐electron PtII complex [Pt(κ 2 PC‐PtBu2CMe2CH2)(PtBu3)]+ with concomitant formation of [Pt(PtBu3)2H]+.

The synthesis of donor-stabilized silacyclobutanone 2 was successfully realized by the reaction of silacyclopropylidene 1 with benzaldehyde in the presence of a Lewis acid catalyst. Of particular interest, silacyclobutanone 2 evolves at room temperature via a retro-[2 + 2]-cycloaddition reaction, leading to an original NHC-stabilized 1-silaketene 4 and cis-stilbene.

Strained but stable: An isolable silacycloprop-1-ylidene stabilized by intramolecular complexation with an iminophosphorus ylide fragment was successfully synthesized and fully characterized. The formation of this small highly strained cyclic silylene involves an unprecedented Si(IV)→Si(II) rearrangement under very mild conditions.

The chemistry of stable silylenes has been the subject of considerable research since the isolation of silicocene [1] and N-heterocyclic silylene. [2] To date, several stable silylenes, [3][4][5] including kinetically stabilized dialkylsilylene, [6] have been synthesized and their chemical properties have been extensively investigated. [7] A novel silylene stabilized by ylidic carbon centers has also recently been reported. [8] However, the structural modifications of stable silylenes are still far more limited than those of their lighter analogues, the carbenes. [9] Recently, silylenes I stabilized by the coordination of a donating ligand to the silicon(II) atom have attracted much attention owing to their high reactivity, which is strongly related to the nature of the ligands. [10][11][12][13] In particular, this stabilization method allows for easy functionalization of the Si(II) atom. Indeed, silylenes with reactive SiÀX bonds II (X = Cl, Br) [11,14] and even dihalogenosilylene complexes III [12] have been isolated as stable crystalline materials and have been used as precursors for preparing unique molecules. [14,15] We have also successfully synthesized the first basestabilized silicon(II) hydride species IV, [16] which are difficult to prepare in the absence of steric protection. [17] In this series, the small highly strained cyclic silylenes, such as the silacycloprop-1-ylidenes V, remain challenging target molecules. [18] Herein, we report the first synthesis of a base-stabilized silacycloprop-1-ylidene 3.We recently reported the synthesis of the first phosphinestabilized silicon(II) hydride 1 and studied the reactivity of the species with olefins. [16] Compound 1 similarly reacts at room temperature with diphenylacetylene through a [2+1] cycloaddition reaction to give the corresponding pentacoordinate silirene 2, which was fully characterized by NMR spectroscopy in solution. A 29 Si NMR analysis of silirene 2 shows a high-field doublet (À135.2 ppm, 1 J SiP = 58.9 Hz), which is characteristic of this type of structure. [19] In the 1 H NMR spectrum, the Si À H fragment appears as a doublet at 6.25 ppm ( 2 J PH = 96.4 Hz) with the characteristic 29 Si satellites (ca. 4.7 %, 1 J HSi = 286.1 Hz), confirming a direct siliconhydrogen bond in 2 (Scheme 1).Silirene 2 is thermally labile and quantitatively isomerizes in toluene at 80 8C into silacycloprop-1-ylidene 3, in which the Si II atom is stabilized by the intramolecular coordination of the imine fragment. Compound 3 was successfully isolated as colorless crystals in 92 % yield from pentane at room temperature (Scheme 1). Although the mechanism of the reaction is still unclear, this transformation formally involves two 1,2shifts of silicon ligands, hydride and phosphine, to each of the carbon atoms of the silirene ring. Contrary to the previous cases, neither an alkyne-insertion into the Si II À H bond [15] nor tricyclic phosphine formation [19] was observed. In the 31 P NMR spectrum, 3 displays two singlets (46.5 and 42.8 ppm), which is in agreement wit...

An isolable donor-stabilized silavinylidene phosphorane was synthesized. This molecule, which can also be regarded as a new carbon(0) complex featuring a phosphine and a donor-stabilized silylene ligand, presents a central carbon atom with a remarkably high electron density (-1.82). Furthermore, the experimental electron-density study of this compound demonstrates the delocalization of the σ-lone pair at the central carbon atom toward the silicon center, a feature which is remarkably different from electronic situation of other bent-allene-type molecules. This result clearly demonstrates the powerful electron-donating ability of donor-stabilized silylene ligands, as well as their excellent electron-acceptor properties.