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, Rh^I(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 Rh^I···Rh^I 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 Rh^I(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, Rh^I(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.