Synthesis of Pd Complexes Containing Tailed NHC Ligands and Their Use in a Semicontinuous Membrane-Assisted Suzuki Cross-Coupling Process

Homogeneous catalysis has proved to be a reliable method for preparing numerous molecular entities, but catalysts can be expensive and difficult to remove. Because of this, industry targets catalysts that are easily separated and recovered and feature increased turnover numbers. The ongoing shift from multipurpose batch reactors toward continuous manufacturing in fine chemicals synthesis results in a new set of catalyst requirements. This paper reports the design and use of Pd complexes suitable for a semicontinuous Suzuki cross-coupling reaction based on a membrane-assisted reactor. These Pd complexes contain tailed N-heterocyclic carbene (NHC) ligands, allowing internal catalyst recovery by organic solvent nanofiltration with top-layer-modified ceramic membranes. These membranes give selective nanofiltration of the catalyst based on a combination of size exclusion and affinity separation (solvent-solute-membrane interactions). The semicontinuous system developed led to significantly improved turnover numbers, simplified product isolation, and consequently reduced mass intensity by simply adding more of the reactants and reagents to the reaction vessel.