Molecular‐Weight‐Enlarged Multiple‐Pincer Ligands: Synthesis and Application in Palladium‐Catalyzed Allylic Substitution Reactions

Bigger is better: PCP pincer ligands are attached to soluble supports of different shapes. Disc‐like structures lead to excellent retention by nanofiltration. High selectivity towards the linear trans products is obtained in palladium‐catalyzed allylic alkylation and amination. The kinetics of an allylic amination reaction are studied and one of the molecular‐weight‐enlarged homogeneous catalysts is applied in a membrane reactor under continuous conditions. magnified image Three different pincer ligand systems are synthesized via nucleophilic substitution reactions of polyaromatic benzyl bromides as support molecules and phenol derivatives as ligand precursors. Retention tests using a polymeric nanofiltration membrane show moderate to good retention in THF and CH 2 Cl 2 . Concentration‐dependent NMR spectroscopy gives no indication for the formation of aggregates in solution. The three ligand systems are active in both the allylic alkylation and allylic amination reactions and show high selectivity towards the linear trans products. An investigation of the kinetic parameters of the allylic amination reaction show that the reaction of cinnamyl acetate with morpholine is of zero order in cinnamyl acetate and of first order in morpholine. The order in catalyst is found to be one, and the rate constant k′ is determined for a reaction under standard conditions. Moreover, one of the tri(pincer)‐palladium complexes is used as soluble, molecular‐weight‐enlarged homogeneous catalyst in continuous allylic alkylation and amination reactions. The conversion of the allylic alkylation reaches a maximum of 30 %, while a maximum conversion of 80 % is reached in the allylic amination reaction. No palladium black was formed.