Immobilization of Rh(i) precursor in a porphyrin metal–organic framework – turning on the catalytic activity

Abstract

Two model porphyrin metal–organic frameworks were used for the incorporation of Rh(I) species by a post-synthetic metallation under mild conditions. As a result, new rhodium MOFs (Rh/MOFs), Rh/PCN-222 and Rh/NU-1102, were synthesized and structurally characterized. To illustrate the potential of this catalytic platform, we use Rh/MOFs as phosphine-free heterogeneous catalysts in the hydrogenation of unsaturated hydrocarbons under mild reaction conditions (30 °C and 1 atm H₂). We found that for our Rh/MOFs an activation step is required during the first run of the catalytic process. The presence of Rh–CO moieties allowed us to monitor the activation pathway of the catalyst under a H₂ atmosphere, by in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). After activation, the catalyst remains highly active during the subsequent catalytic cycles. This simple post-synthetic modification approach presents new possibilities for the utilization of Rh-based catalytic systems with robust porphyrin-based MOFs as supports.