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Van 't Hoff Institute for Molecular Sciences Van 't Hoff Institute for Molecular Sciences

Encapsulated rhodium catalyst yields branched aldehydes via hydroformylation of terminal alkenes

27 February 2024

A paper by PhD student Pim Linnebank and supervisors at the Homogeneous, Supramolecular and Bio-Inspired Catalysis group of the Van 't Hoff Institute for Molecular Sciences describes the potential of an encapsulated rhodium catalyst in the hydroformylation of terminal alkenes to yield branched aldehydes. Published in the RSC journal Catalysis Science & Technology, the study explored the substrate scope by investigating 41 terminal alkenes. Combining the experimental results with DFT calculations led to an optimized catalyst capable of converting substrates with higher branched selectivity.
Image: HIMS / Catal.Sci.Technol.

Obtaining branched aldehydes from terminal alkenes has long been a notorious challenge in the field of hydroformylation catalysis. Linnebank and his supervisors Prof. Joost Reek and Dr Sander Kluwer took up this challenge by encapsulating a rhodium catalyst in a porphyrin-based supramolecular cage. They reacted 41 terminal alkenes with this caged catalyst to target branched aldehydes in the hydroformylation reaction. By varying the porphyrin building blocks, they were able to further enhance the selectivity towards the desired branched products.

Abstract of the paper

Caged complexes can provide impressive selective catalysts. Due to the complex shapes of such caged catalysts, however, the level of selectivity control of a single substrate cannot be extrapolated to other substrates. Herein, the substrate scope using 41 terminal alkene substrates is investigated in the hydroformylation reaction with the encapsulated rhodium catalyst [Rh(H)(CO)3(P(mPy3(ZnTPP)3))] (CAT1). For all substrates, the amount of branched product formed was higher with CAT1 than with the unencapsulated reference catalyst [Rh(H)(CO)2(P(mPy3))2](CAT2) (linear/branched ratio between 2.14 and 0.12 for CAT1 and linear/branched ratio between 6.22 and 0.59 for CAT2). Interestingly, the level of cage induced selectivity depends strongly on the substrate structure that is converted. Analysis of the substrate scope combined with DFT calculations suggest that noncovalent interactions between the substrate moieties and cage walls play a key role in controlling the regioselectivity. Consequently, these supramolecular interactions were further optimized by replacing the ZnTPP building block with an zinc porphyrin analog that contained OiPr substituents on the meta position of the aryl rings. The resulting caged catalyst, CAT4, converted substrates with even higher branched selectivity.

Paper details

Pim Linnebank, Sander Kluwer and Joost N. H. Reek: A Substrate Scope Driven Optimization of an Encapsulated Hydroformylation Catalyst Catal. Sci. Technol., 2024, accepted 16 Feb 2024 DOI: 10.1039/D4CY00051J

See also

Research group Homogeneous, Supramolecular and Bio-inspired Catalysis