N-heterocyclic carbenes incorporated in porous networks

可重复使用催化剂系统的设计与设计是绿色工艺工程中的一个关键问题。多相催化的概念通常可以实现催化剂的可回收利用，但金属浸出、催化剂中毒和催化剂变质等因素往往限制了这种方法的适用性。CAPONE项目侧重于固定化非杂环碳的新概念。近年来，金属NHC作为一种用途广泛的新型催化剂出现，可在极其温和的条件下进行许多反应。这种NHC的固定化将使其一方面具有高催化活性，另一方面具有可回收性。使用双功能碳前体，多孔网络将通过自下而上的方法合成，将NHC作为多孔材料的固有部分，而不是仅仅从预成型的支架上接枝。我们将重点阐述两种含NHC物质的多孔材料：•亲水周期介孔有机硅（PMOs）和•疏水有机聚合物网络。对于非均相催化的应用，反应介质和非均相催化剂的极性调整是必要的。由于这个原因，在水介质中使用PMOs可能很有趣，而在使用有机溶剂时，有机聚合物网络更有用。我们认为这些材料作为多相催化剂体系具有很大的潜力，原因如下：1)所用载体的高孔隙率确保了固定化NHC的可及性；2)由于NHC通过双重键紧密结合到多孔网络中，因此催化剂的化学和形态稳定性应该得到强烈增强。

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.