Abstract
The combination of supported ionic liquids and immobilized NHC–Pd–RuPhos led to active and more stable systems for the Negishi reaction under continuous flow conditions than those solely based on NHC–Pd–RuPhos. The fine tuning of the NHC–Pd catalyst and the SILLPs is a key factor for the optimization of the release and catch mechanism leading to a catalytic system easily recoverable and reusable for a large number of catalytic cycles enhancing the long-term catalytic performance.
Highlights
N-heterocyclic carbenes (NHCs) are known as efficient coordination ligands for different types of metals
The amount of immobilized NHC ligand was determined by elemental analysis, while the palladium loaded on the polymer was determined by ICP analyses
The capacity to generate active catalytic species from the MNPs is essential in the first run, but the capacity of the system, including imidazolium fragments and remaining MNPs, to efficiently recapture the soluble species in an active form is key for the second and successive runs. All these results suggest that the supported ionic liquid-like phases (SILLPs) can be used as efficient scavengers for the palladium-leached species released from NHC–Pd–RuPhos complexes, limiting the leaching and possibly improving the long-term system stability
Summary
N-heterocyclic carbenes (NHCs) are known as efficient coordination ligands for different types of metals. We report our efforts aiming a rational development for Negishi catalysts based on NHC–Pd complexes in conjunction with supported ionic liquid-like phases to enhance their catalytic stability under continuous flow conditions. The Negishi reaction of benzylzinc bromide (5) and methyl 4-bromobenzoate (6) to form methyl 4-benzylbenzoate (7) was used to evaluate the activity of the palladium catalysts on polymer support (Scheme 2).
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