A mesoionic bis(Py-tzNHC) palladium(ii) complex catalyses “green” Sonogashira reaction through an unprecedented mechanism

Abstract

A novel bis(pyridyl-functionalized 1,2,3-triazol-5-ylidene)-palladium(II) complex [Pd(Py-tzNHC)2](2+) catalyses the copper-, amine-, phosphine-, and additive-free aerobic Sonogashira alkynylation of (hetero)aryl bromides in water as the only reaction solvent. The catalysis proceeds along two connected Pd-cycles with homogeneous bis-carbene Pd(0) and Pd(II) species, as demonstrated by electrospray ionization mass spectrometry.

Metal Complexes of Click-Derived Triazoles and Mesoionic Carbenes: Electron Transfer, Photochemistry, Magnetic Bistability, and Catalysis

“…Apart from palladium complexes containing ligands L15 , various mono‐, di‐ and trinuclear palladium(II) complexes were reported with the ligands L19 , L23 , L24 , L28 , L29 , and L30 (Figure ). [95f], [100c], [103f], Complex 115 2+ is a dicationic complex and is unique amongst all reported palladium‐triazolylidene complexes because of its double positive charge. [104a] Additionally, in contrast to the “normal” PEPPSI type complexes such as 113 , in complex 115 the pyridine rings are attached to the MIC ligands, making such complexes probably more sustainable than the PEPPSI type complexes 113 (where the monodentate pyridine ligands are known to dissociate from the complex during catalysis).…”

“…PEPPSI‐type di‐ and trinuclear complexes 116 / 117 and 118 were synthesized with the ligands L23/L24 and L28 . [104b] The trinuclear complex 119 was prepared with the ligand L30 . [100c]…”

“…The reaction of choice has been the Suzuki‐Miyaura cross‐coupling, and a majority of the complexes presented above were used as pre‐catalysts for that reaction . Apart from this, some of the complexes were used as pre‐catalysts for the Hiyama coupling, Buchwald‐Hartwig amination,, [103m] Mizoroki‐Heck reactions,[103f] Sonogashira reaction,[104a] and for α‐arylation and α‐methylation reactions. [100c], The most efficient palladium‐triazolylidene catalysts for the Suzuki‐Miyaura cross‐coupling reaction are of the PEPPSI type.…”

Carbon Nanotube‐supported Pd/Ni(OH)2 Nanoparticles: Magnetically Recoverable and Reusable Catalyst for the Reduction of Nitroarenes

“…The use of palladium (Pd) nanoparticles in catalysis has been the subject of intense research owing to its scientific and commercial importance . However, owing to their aggregation, catalytic Pd nanoparticles are often converted to non‐catalytic Pd black during the reaction.…”

“…The use of palladium (Pd) nanoparticles in catalysis has been the subject of intense research owing to its scientific and commercial importance. [1][2][3][4][5] However, owing to their aggregation, catalytic Pd nanoparticles are often converted to non-catalytic Pd black during the reaction. At present, the use of these nanoparticles still suffers from a number practical drawbacks such as difficulty of catalyst recovery, limited catalyst reusability, and product contamination.…”