Insight into the dual action mechanism of 3V-PPh3 polymers as carriers and ligands in the Rh/3V-PPh3 heterogeneous catalytic hydroformylation of ethylene to propionaldehyde

Abstract

An experimentally confirmed porous vinyl-functionalized PPh₃ (3V-PPh₃) polymer-supported Rh-based catalyst exhibits the significant advantages of high activity, high stability, and easy separation in the synthesis of propionaldehyde, which fundamentally solves the problem of Rh precious-metal loss. In this paper, the microscopic mechanism and electronic structure characteristics of two kinds of cross-linked 3V-PPh₃ polymer-supported Rh-based catalyst were studied by means of quantum chemistry (QC). With 3V-PPh₃ as the carrier, stable adsorption configurations of Rh and 3V-PPh₃ were investigated, and the results showed that Rh and P had the strongest effects, while the vinyl group enhanced the adsorption strength of Rh. Moreover, it was found that a high concentration of exposed P was beneficial to the dispersion of Rh. With 3V-PPh₃ as the ligand, the properties of the HRh(CO)(P-frame)₃ complex were investigated, and the results of structure analysis indicated that there were strong interactions between Rh and P, which contributed more to the non-loss of Rh. Among the four different configurations, the Rh–P coplanar configuration of cross-linking mode 2 had the highest Rh–P bond energy. The results of AIM analysis suggested that the Rh–P and Rh–C(CO) bonds involve closed-shell (donor–acceptor) interactions. The Mulliken charge and molecular electrostatic potential results revealed that the Rh activity of the Rh and P non-coplanar configuration was higher in the two cross-linking methods. Hopefully, this work will clarify the structure–activity relationship between 3V-PPh₃ polymer and Rh, and provide theoretical guidance for the design and development of high-efficiency heterogeneous catalysts for the hydroformylation of ethylene to propionaldehyde.