N-heterocyclic carbenes incorporated in porous networks

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The elaboration and the design of re-usable catalyst systems is a key issue in green process engineering. The concept of heterogeneous catalysis often allows to achieve recyclable catalysts, but factors such as metal leaching, catalyst poisoning and catalyst deterioration often limit the applicability of this approach. The CAPONE project focuses on new concepts towards the immobilization of Nheterocyclic carbenes. Metallic NHC species recently appeared as a particularly versatile new class of catalysts for numerous reactions under extremely mild conditions. The immobilisation of such NHC species would allow to combine high catalytic activity on one side and recyclability on the other side. Using bifunctional carbene precursors, porous networks will be synthesized by a bottom-up approach featuring the NHC as inherent part of the porous material instead of just grafting it from a pre-formed support. We will focus on the elaboration of two types of porous materials bearing NHC species: • hydrophilic periodic mesoporous organosilicas (PMOs) and • hydrophobic organic polymer networks For applications in heterogeneous catalysis, the adjustment of the polarity of the reaction medium and the heterogeneous catalyst can be desirable. For this reason, the use of PMOs may be interesting in aqueous media, whereas organic polymer network are more useful when organic solvents are employed. We believe that these materials have great potential as heterogeneous catalyst systems for the following reasons: i) high porosity of the used supports that ensures accessibility of immobilized NHC species, ii) Chemical and morphological stability of the catalyst should be strongly enhanced due to the dense incorporation of the NHC into the porous network by the twofold-bonding.