P,C-palladacycle complexes of triphenylphosphite: Synthesis, characterization and catalytic activity in the Suzuki cross-coupling reaction

Five-membered P,C-palladacycles were synthesized through the reaction of the binuclear triphenylphosphite complex [Pd(μ-Cl)P(OPh)2(OC6H4)]2 (1) with different monodentate ligands [L = triphenylphosphine (PPh3), thiourea (tu), 2,4,6-trimethylpyridine (Me3Py), pyridine (Py)] and bidentate ligands [N^N = 1,10-phenanthroline (Phen), 4-methyl-1,10-phenanthroline (MePhen)], giving mononuclear P,C-palladacycles [Pd(L)(Cl){P(OPh)2(OC6H4)}] [L = PPh3 (2a), tu (2b), Me3Py (2c)], [PyH]+[Pd(Cl)2{P(OPh)2(OC6H4)}]− (3d) and [Pd(N^N){P(OPh)2(OC6H4)}]+ NO3− [N^N = Phen (4a), MePhen (4b)]. The synthesized complexes were characterized by 1H, 13C–{1H} and 31P–{1H} NMR spectroscopy, elemental analysis and FT-IR techniques. Structural details of complexes 2a, 2c and 3d were determined by X-ray crystallography, which showed these complexes crystallize in the triclinic (2a) and monoclinic (2c and 3d) crystalline systems. According to the structural data, the orthopalladated complex 3c has two different conformers (R,S) in the solid state, although it appeared as one isomer in the solution state, as confirmed by the NMR spectroscopy. Complex 2a, containing PPh3, was evaluated as a homogeneous catalyst for a variety of substrates, affording coupled products in good to excellent yields, importantly at room temperature. Furthermore, the use of the lesser reactive aryl chloride as a substrate in the Suzuki reaction under mild conditions, has received much attention.

The orthopalladated complexes of triphenylphosphite with mono- and bidentate ligands were synthesized and fully characterized. The P,C-orthopalladated complex containing triphenylphosphine was used as an efficient homogeneous catalyst in the Suzuki cross-coupling reaction.Figure optionsDownload as PowerPoint slide