​Thermal treatment of phosphotungstic acid (PTA)-MIL-101(Cr) composites in the presence of hydroformylation catalyst RhH(CO)(PPh₃)₃ leads to immobilization of the homogeneous Rh complex within the metal–organic framework (MOF) scaffold by coordination of PTA-Rh. The Rh complex-containing MOFs are tested in the hydroformylation of 1-octene in which PTA competes with CO during ligand association. In the presence of the carbonyl ligand, the Rh complex is released from the MOF and behaves as a homogeneous catalyst. Therefore, the product spectra and selectivities of the Rh complex-containing MOFs are similar to those of RhH(CO)(PPh₃)₃. Upon CO evacuation, Rh recoordinates to PTA, allowing for easy recycling of this new pseudo-heterogeneous catalyst.