Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Nat Chem. 2012 Nov;4(11):947-52. doi: 10.1038/nchem.1465. Epub 2012 Sep 30.
A combination of the advantages of homogeneous and heterogeneous catalysis could enable the development of sustainable catalysts with novel reactivity and selectivity. Although heterogeneous catalysts are often recycled more easily than their homogeneous counterparts, they can be difficult to apply in traditional organic reactions and modification of their properties towards a desired reactivity is, at best, complex. In contrast, tuning the properties of homogeneous catalysts by, for example, modifying the ligands that coordinate a metal centre is better understood. Here, using olefin cyclopropanation reactions catalysed by dendrimer-encapsulated Au nanoclusters as examples, we demonstrate that changing the dendrimer properties allows the catalytic reactivity to be tuned in a similar fashion to ligand modification in a homogeneous catalyst. Furthermore, we show that these heterogeneous catalysts employed in a fixed-bed flow reactor allow fine control over the residence time of the reactants and thus enables the control over product distribution in a way that is not easily available for homogeneous catalysts.
均相和多相催化的优点结合起来，可以开发出具有新颖反应性和选择性的可持续催化剂。虽然多相催化剂通常比均相催化剂更容易回收，但它们在传统有机反应中的应用可能很困难，并且对其性质进行修饰以达到所需的反应性是非常复杂的。相比之下，通过例如修饰与金属中心配位的配体来调整均相催化剂的性质，人们对此有更好的理解。在这里，我们以树枝状大分子包裹的金纳米簇催化的烯烃环丙烷化反应为例，证明改变树枝状大分子的性质可以使催化反应性以类似于均相催化剂中配体修饰的方式进行调节。此外，我们还表明，这些在固定床流动反应器中使用的多相催化剂可以很好地控制反应物的停留时间，从而可以控制产物分布，这对于均相催化剂来说是不容易实现的。
