Synthesis of Bis-P,N,P-hybrid Ligands and Application to Pd-Catalyzed Aminocarbonylation of Phenylacetylene with Aniline Free of Additive and Solvent

Aminocarbonylation of alkynes with organic amines as an attractive straightforward protocol for the synthesis of high-value-added α,β-unsaturated amides is highly in demand, which is highly dependent on the performance of Pd catalysts modified by the elaborately designed ligands with various stereoelectronic properties. Herein, the bis-P,N,P-hybrid ligands (L2-L4) were successfully synthesized by using low-cost and easily handleable bis(2-chloroethyl)amine hydrochloride as the starting material. The complexation of L2 with Pd(CF₃COO)₂ could afford a stable binuclear complex L2 with an ideal centrosymmetric configuration, which proved that L2 served as the bis-P,P-bidental chelating ligand. It was found that L2-modified Pd(CF₃COO)₂ (or Pd-L2) could catalyze aminocarbonylation of phenylacetylene with aniline free of any additive and organic solvent, affording the branched product N,2-diphenylacrylamide (3a) with 100% regio-selectivity in the isolated yield of 90%. However, the generality of the developed L2-Pd(CF₃COO)₂ catalytic system is very limited.