Rh Catalyzed Selective Hydrogenation of Nitroarenes under Mild Conditions: Understanding the Functional Groups Attached to the Nanoparticles

Graphical Functionalized surfaces : Rh nanoparticles supported on magnetic silica spheres with various functional groups were tested in the catalytic hydrogenation of nitroarenes under mild conditions. Electron-donating groups can effectively increase the electron density of catalytic sites and the ratio of Rh 0 /Rh 3+ , which results in the promotion of the selectivity of the catalyst for hydrogenation at room temperature under atmospheric conditions. Modifying the surface of metal catalyst is a crucial subject for improving the heterogeneous metal catalysts. It is still a great challenge to understand the structure-activity relationship (SAR) between the surface supporting groups and the metal particles. Herein, Rh NPs supported on the magnetic silica sphere with various functional groups (−NH 2 , −SH, −SO 3 H, −N=CH 2 , −Cl, −NHCOCH 3 and −NHCH 2 Ph) have been prepared for catalytic hydrogenation of nitroarenes under atmospheric pressure at room temperature. We discover that the chemical state of Rh NPs depends on the supporting groups significantly. The electron-donating functionalities can effectively elevate the Rh 0 /Rh 3+ ratio, which increase the catalytic performance both in conversion and selectivity. The amino group decorated catalyst has such a good selectivity that no dechlorination reaction is observable in the hydrogenation of 2-chloro-3-nitropyridine. What's more, by introducing magnetic Fe 3 O 4 nuclei and mesoporous silica encapsulating layer, the catalyst can be recovered conveniently by an external magnet, and can be reused 10 cycles without any loss of activity.