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 center dot center dot center dot P distance of 4.31 A and 4.36 A 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, 12' based PdCl2(MeCN)(2) system immobilized in RTIL of [Bmim]NTf2 could be recycled for 7 runs without obvious activity loss or metal leaching. (C) 2019 Elsevier Inc. All rights reserved.