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

Abstract 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) 2 Pd(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 μ 2 -I 2 bridged complexes 5 and 6 of the type [(MIC)PdI 2 ] 2 were obtained as unique products. Additionally, the preparation of the heteroleptic PEPPSI-type complexes ([Py(PdI 2 )MIC]) 7 and 8 was readily achieved by the thermal treatment of the triazolium precursors with PdCl 2 , K 2 CO 3 , and sodium iodide in pyridine. All complexes have been fully characterized by 1 H and 13 C NMR, FT-IR, elemental analysis, and in the case of 2, 3 trans , 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.