Structural diversity of phenoxy functionalized triazol-5-ylidene palladium(II) complexes and their application in C–N bond formation

The preparation and isolation of a variety of mono-, bis-, and heteroleptic mesoionic triazol-5-ylidene palladium(II) complexes is reported. Treatment of phenoxy functionalized triazolium salts [Bn-MIC(H)]+I− (1) and [Mes-MIC(H)]+I− (2) with half equivalent of palladium acetate, produced complexes 3 and 4 with a general structure of [(MIC)2Pd(I)2] as isomeric cis/trans mixtures. When the reaction of palladium acetate and the cationic precursors was carried out with equimolar amounts in presence of sodium iodide, the μ2-I2 bridged complexes 5 and 6 of the type [(MIC)PdI2]2 were obtained as unique products. Additionally, the preparation of the heteroleptic PEPPSI-type complexes ([Py(PdI2)MIC]) 7 and 8 was readily achieved by the thermal treatment of the triazolium precursors with PdCl2, K2CO3, and sodium iodide in pyridine. All complexes have been fully characterized by 1H and 13C NMR, FT-IR, elemental analysis, and in the case of 2, 3trans, 6, and 7 single crystal X-ray diffraction. Preliminary catalytic results with the palladium series established the enhanced performance of PEPPSI complexes 7 and 8 in the Buchwald-Hartwing catalyzed formation of C–N bonds between aryl halides and primary/secondary amines under mild reaction conditions.