Bandeau ECOIH

Unique silicon species stabilized by phosphine ligands

- Is it possible to synthesize silicon version of Wittig reagents ?

Phosphorous ylides are perfectly stable and are widely used in organic synthesis as Wittig reagents. In marked contrast, phosphorus sila-ylides, the silicon analogues, were completely unknown. We are interested in finding how to stabilize such a molecule which should be an excellent chemical tool in silicon chemistry.

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Phosphorus sila-ylides can also be regarded as a silylenes complexed by a phosphine ligand. This kind of complex is actually labile and it dissociates easily. Thus, we considered to stabilize such a molecule by connecting the two fragments (phosphine and silylene) by a rigid spacer, and the resulting phosphorus sila-ylides are perfectly stable at room temperature. Of particular interest, these derivatives present a similar reactivity to that observed with classical Wittig reagents (J. Am. Chem. Soc. 2009, 131, 8762

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 - P-Chiral phosphine as strong nucleophiles as NHCs!

Silylene complexes react with alkynes to afford diastereoselectively tricyclic P-chiral phosphines (J. Am. Chem. Soc. 2010, 132, 12841). These phosphines present a nucleophilic character as strong as that of N-heterocyclic carbenes (NHCs). Taking into account their unique properties (nucleophilic character and steric hindrance), we expect to find interesting applications of these new ligands in asymmetric catalysis.

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- Extremely strained but stable three-membered cyclic silylene!

We recently succeeded to synthesize the first stable silylene incorporated into a small three membered ring (Angew. Chem. Int. Ed. 2012, 51, 7158). This base-stabilized silacyclopropylidene possess unique properties and is an excellent ligand for transition metals.

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- Disilyne (-Si≡Si-) complexes: Reducing agent for CO2 to CO!

In organic chemistry, triply bonded species such as alkynes (-CC-) are common compounds, which allow to construct complex molecular architectures. In contrast, in silicon chemistry, although some stable disilynes (-SiSi-) have been recently described, the synthesis of such molecules remains very difficult because of their extremely high reactivity. In the group we have succeeded in the synthesis of a new type of disilyne stabilized by complexation of both silicon centers.

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Interestingly, this new disilyne phosphine bis-adduct reacts at room temperature with four equivalents of carbon dioxide (CO2), allowing the non-metal mediated direct reduction of CO2 to CO without any catalyst. Taking into account the difficulty of CO2 reduction to CO, this reaction could help to develop new efficient methodologies to use CO2 in a much better way.

The first stable, and still unique, molecule featuring a -Si≡C- triple bond !

The first persistent silyne presenting a silicon-carbon triple bond (-SiC-) has been recently synthesized. In this molecule, the highly reactive silyne function is efficiently stabilized by coordination of a phosphine ligand on the silicon atom. In spite of this coordination, it presents an extremely short Si-C distance (1.67 Å) within the range of the values predicted by theoretical calculations (1.63 - 1.67 Å) (Angew. Chem. Int. Ed. 2010, 49, 6585). It is worth noting that, to date, this is the only one silyne ever reported.

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