Carbon Modifications and Surfaces for Catalytic Organic Transformations

Carbon is anything but a new material, yet ubiquitously applicable for many catalytic transformations in modern organic chemistry. It is highly versatile, as it occurs as modifications abundantly available as 1-3D carbonaceous materials due to technical progress. In addition, materials such as activated charcoal, ordered mesoporous carbon (OMC), graphite and graphene (oxide), carbon nanotubes (CNTs), nanospheres (nanoonions, fullerenes), and many others are no innocent supports, as demonstrated by many recent publications within the revitalized field of carbocatalysis. By nature, carbon scaffolds offer a perfect link between nanoscaled matter and organic molecules, which makes them an ideal cornerstone for molecular catalysts. Apart from this inherent chemical significance, the physical properties (e.g., different conductivity) are equally important for the performance of heterogeneous or immobilized homogeneous catalysts. Careful selection of the carbon scaffold enables control of reactivity by tuning the electronic interactions of active sites with the support or among each other. Moreover, separation and recycling of heterogenized catalysts can be further improved by rendering carbon magnetic, that is, by incorporation of magnetic particles or by coating metal nanomagnets with graphene-like shells. Altogether, tuning the properties of carbon supports might lead to catalysts tailored not only in matters of reactivity (electron shuttle), but also to down-to-earth problems such as purification (magnetic separation and recycling). This critical review will highlight how far such concepts have already been implemented in the design of heterogenized catalysts and is meant to widen the perspectives where certain concepts have yet to be realized.