New PEGylated Xantphos ligands for palladium-catalyzed hydroesterification and enhanced recovery via organic solvent nanofiltration

Homogeneous catalyst recovery from organic media has always been a major challenge and targeted objective. In this work, five new modified Xantphos ligands bearing methyl ester groups, various poly(ethyleneglycol) (PEG) or long aliphatic chains, with molecular weights ranging from 871 to 2413 g.mol –1 (compared to original Xantphos, 587 g.mol –1 ) were synthesized and fully characterized. As part of the synthetic route, a dibrominated Xantphos intermediate was prepared, providing a versatile precursor for the synthesis of structurally diverse Xantphos derivatives through subsequent functionalization. All ligands were evaluated in a palladium-catalyzed hydroesterification reaction of methyl 10-undecenoate in toluene, to investigate the influence of the ligand functional groups on the catalytic performance. The rejection of the catalysts was determined using several organic solvent nanofiltration (OSN) experiments, effectively decreasing the catalyst leaching through the polymeric membrane from 13% to below ICP-AES detection limit. The synthesized ligands exhibited catalytic activities and selectivities comparable to those of conventional Xantphos while showing enhanced membrane rejection. The relationship between ligand structure, catalytic performance and rejection via membrane demonstrates that rational PEG modification enables an effective balance between catalytic efficiency and recoverability. These findings establish PEG-functionalized Xantphos ligands as promising candidates for recovery via membrane and further showcase the versatility of a new dibrominated Xantphos intermediate as a valuable building block for the future development of new ligands.