Recyclable supported Pd-NHC catalytic systems for the copper-free Sonogashira cross-coupling in flow

Abstract

A new family of well-defined NHC-Pd complexes immobilised onto silica, alumina and titania is reported. The catalysts display activity and recyclability in the Sonogashira cross-coupling reactions under batch and continuous flow conditions. Under batch conditions the new catalytic systems were recycled up to four times with yields over 80%. These catalysts have a broad substrate scope of different aryl bromides and alkynes. The titania-supported catalysts show good conversions under continuous flow conditions at least over 8 hours on stream using MeOH as solvent.

Recent Advancements in Continuous‐Flow Suzuki‐Miyaura Coupling Utilizing Immobilized Molecular Palladium Complexes

“…[51][52][53][54][55][56][57][58][59] Hence, the practical application of this catalyst type without the need for pre-treatment in continuous-flow Suzuki-Miyaura coupling is highly promising. [55][56][57][58][59] Additionally, in the 2000s, various catalytic systems and reaction techniques for microscale Suzuki-Miyaura coupling under flow conditions emerged. Examples include coating a Pd film on a capillary tube and immobilizing a polymeric Pd complex membrane in a microchannel device.…”

“…In contrast to supported Pd NPs, anchoring the Pd complex to a solid support containing appropriate coordination sites and tailored structural design is anticipated to maintain its catalytic stability during the reaction. [51][52][53][54][55][56][57][58][59] Hence, the practical application of this catalyst type without the need for pre-treatment in continuous-flow Suzuki-Miyaura coupling is highly promising. [55][56][57][58][59] Additionally, in the 2000s, various catalytic systems and reaction techniques for microscale Suzuki-Miyaura coupling under flow conditions emerged.…”

“… [35] Consequently, catalytic deactivation and product contamination caused by Pd leaching under the continuous‐flow conditions are generally difficult to avoid. In contrast to supported Pd NPs, anchoring the Pd complex to a solid support containing appropriate coordination sites and tailored structural design is anticipated to maintain its catalytic stability during the reaction [51–59] . Hence, the practical application of this catalyst type without the need for pre‐treatment in continuous‐flow Suzuki‐Miyaura coupling is highly promising [55–59] .…”