Catalytic Hydroformylation of Alkenes to Branched Aldehydes by Triphenylphosphine-Based Porous Organic Polymer-Anchored Rhodium Cluster Catalysts

Hydroformylation of alkenes to high-value-added aldehydes is one of the most important processes in the chemical industry. The use of heterogeneous hydroformylation catalysts encounters substantial challenges including low catalyst activity and stability as well as difficulties in achieving high selectivity for branched aldehydes. In this work, a porous organic polymer (POP) system with embedded triphenylphosphine ligands was prepared, and through impregnation, reduction, and anchoring, rhodium was immobilized on the PPh₃-p-Ph₄ material as rhodium clusters. Triphenylphosphine exerts significant steric hindrance toward selective alkene hydroformylation, and using water as a solvent also demonstrated pronounced electronic effects, resulting in a high selectivity toward branched aldehydes with a branched-to-linear ratio of more than ten. Mechanistic studies confirmed that the reaction to the branched aldehydes follows pathways with lower reaction energy, thus achieving a high selectivity and yield (95.4%) of branched products. Importantly, the catalyst can be easily recovered and reused while maintaining its activity and selectivity over five cycles without significant losses. The utilization of triphenylphosphine ligands for the preparation of POP supports for rhodium catalysts not only enables the heterogenization of homogeneous complex catalysts but also presents novel ideas and methodologies for future research on alkene hydroformylation to produce branched aldehydes.