A Carrier-Free Recyclable Rh/Terpyridine Catalyst for Alkene Hydroformylation: Homogeneous Catalysis and Heterogeneous Separation

Hydroformylation of alkenes is one of the most important industrial processes for the production of value-added aldehydes. A new square-planar geometry rhodium(I) complex, RhI(CO)(terpyridine), has been synthesized and characterized using nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS), single-crystal X-ray diffraction (XRD), and scanning electron microscopy (SEM). This complex crystallizes in a self-replicating manner through RhI···RhI and π–π interactions at room temperature, allowing it to function as a carrier-free recyclable rhodium catalyst in the hydroformylation of various alkenes, which effectively addresses the challenge associated with the separation of catalysts from products. The unique packing model enables the RhI(CO)(terpyridine) complex to partially dissolve under hydroformylation conditions, thereby acting as a homogeneous catalyst. Furthermore, it maintains both consistent reactivity and structural integrity for cyclohexene hydroformylation reactions over 10 recycling runs under standard reaction conditions (40 bar, 100 °C, and 4 h). Additionally, RhI(CO)(terpyridine) integrated the advantages of homogeneous catalysis and heterogeneous separation, as demonstrated by its high reactivity and robust recyclability in the hydroformylation of long-chain C6–C18 alkenes, α-methylstyrene, and mixed octenes, highlighting its potential for industrial applications.