Synthesis of new Pro-PYE ligands as co-catalysts toward Pd-catalyzed Heck–Mizoroki cross coupling reactions

Abstract

The present research work describes the synthesis of five new ligands containing pyridinium amine, [H₂L¹][OTf]₂–[H₂L⁵][I]₂ from two new precursors, [P³_Et][I] and [P²_Me][CF₃SO₃]. The structure elucidations of the compounds were confirmed by multinuclear NMR (¹H, ¹³C), FT-IR and by single crystal XRD techniques. Theoretical DFT studies were carried out to get better insight into the electronic levels and structural features of all the molecules. These synthesized new Pro-PYE ligands [H₂L¹][OTf]₂–[H₂L⁵][I]₂ were found to be significantly active as co-catalysts for Pd(CH₃CO₂)₂ toward Heck–Mizoroki coupling reactions with wide substrate scope in the order of [H₂L¹][OTf]₂ ≫ [H₂L²][OTf]₂ > [H₂L³][OTf]₂ > [H₂L⁴][OTf]₂ > [H₂L⁵][I]_2.