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.