Novel multi-dentate phosphines for Pd-catalyzed alkoxycarbonylation of alkynes promoted by H₂O additive

A series of novel multi (bi-/tri-/tetra-)-dentate phosphines with good robustness against water and oxygen were synthesized and fully characterized. It was found that the developed ionic tri-dentate phosphine (L2′) enabled Pd-catalyzed alkoxycarbonylation of alkynes most efficiently while H₂O was used as an additive instead of acid. As for L2′, its unique steric configuration with two types of potential P-P chelation modes (P⋯P distance of 4.31 Å and 4.36 Å respectively) to Pd-centre rendered the corresponding Pd-catalyst high activity and good stability for alkoxycarbonylation of alkynes. The in situ FT-IR analysis also verified that the formation and stability of Pd–H active species were greatly facilitated with the presence of L2′ as well as H₂O additive. In addition, as an ionic phosphine, L2′ based PdCl₂(MeCN)₂ system immobilized in RTIL of [Bmim]NTf₂ could be recycled for 7 runs without obvious activity loss or metal leaching.