Preparation and application of air-stable P,N-bidentate ligands for the selective synthesis of δ-lactone via the palladium-catalyzed telomerization of 1,3-butadiene with carbon dioxide

Air-stable P,N-bidentate ligands L1–L7 with cyclic secondary amine moieties linked to the benzene rings of triphenylphosphine were designed and prepared. The chelating coordination mode of the P,N-bidentate ligands to the Pd(II) center was confirmed by determining the X-ray structures of the Pd(II) complexes C1 and C2 derived from ligands L1 and L2, respectively. The ligands were used for the selective synthesis of δ-lactone through the palladium (Pd)-catalyzed telomerization of 1,3-butadiene with carbon dioxide. The highest yield (60% with 79% selectivity) was observed using the Pd2(dba)3/4-(2-(diphenylphosphino)phenyl)morpholine (L2) catalyst system.