Multiple-Functional Diphosphines: Synthesis, Characterization, and Application to Pd-Catalyzed Alkoxycarbonylation of Alkynes

A series of diphosphine ligands (L1-L5) containing bis-phosphino fragments and bis-amido groups as well as intensive electron-withdrawing F atoms were synthesized and fully characterized. The structures of the prepared complex of Pd-L5 demonstrate that as for L5, the incorporated two phosphino fragments participate in the chelation to the Pd center inversely along with two Cl^-ligands to present a typical square-planar configuration, whereas the two amido groups simultaneously develop a hydrogen-bond interaction with Cl^-ligands to facilitate the timely dissociation of Cl^-ligands from the Pd center. It was found that L5 enabled the Pd complex to be more active in the alkoxycarbonylation of alkynes with MeOH for the synthesis of branched/linear α,β-unsaturated carboxylic esters with general yields of 60-89%. In L5, the incorporated diphosphino fragments, diamino groups, and F atoms conferred a catalytic effect to the Pd complex synergetic toward the reaction.