Synthesis, characterization and low temperature self assembling of (η3-allyl)palladium complexes with 2-pyridyl-1,2,3-triazole bidentate ligands. Study of the catalytic activity in Suzuki–Miyaura reaction

The cationic complexes [Pd(η3-C3H5)(2-((4-propyl-1H-1,2,3-triazol-1-yl)methyl)pyridine)](X) (2: X = BF4−, 3: X = ClO4−), and [Pd(η3-2-CH3-C3H4)(2-((4-propyl-1H-1,2,3-triazol-1-yl)methyl)-pyridine)](BF4−) (4) have been synthesized by reacting the appropriate palladium-allyl precursor with 2-((4-propyl-1H-1,2,3-triazol-1-yl)methyl)pyridine in the presence of AgBF4 or AgClO4. The solid-state structure of 2 has been determined by single-crystal X-ray diffraction analysis. According to 1H NMR spectroscopy the allyl protons undergo syn–syn, anti–anti exchange. 1H NMR spectroscopy reveals that in acetone at temperatures lower than 223 K these complexes form aggregates the stability of which is attributed to solvophobic interactions. Complex 2 is an active catalyst for the S–M coupling of aryl bromides with phenylboronic acid; good reaction rates are obtained only with activated substrates, whereas with deactivated substrates catalyst decomposition to palladium black occurs.

Graphical abstractA new palladium-allyl complex containing a chelating pyridyl-triazole ligand has been characterized by X-ray analysis and the allyl dynamics investigated by variable temperature NMR.1H NMR spectroscopy shows that at low temperature the complex forms ordered aggregates (likely dimers by DOSY). The complex is an active catalyst for S–M coupling.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A new Pd(II)-allyl complex with a pyridyl-triazole chelating ligand was prepared. ► The allyl complex was characterized by NMR techniques and X-ray crystallography. ►1H NMR showed that the complex forms aggregates in acetone at low temperature. ► The catalytic activity of the new complex was assessed in S–M cross coupling.