Palladium complexes based on tridentate pyrazolyl-ligands: Synthesis, structures and use in Suzuki cross-coupling reactions

The reaction of [PdCl(Me)(cod)] (cod = 1,5-cyclooctadiene) with tridentate bis(pyrazolyl) ligands affords the alkyl-palladium(II) complexes [Pd(CH3)(NZN)][BF4] (1, NZN = 1,1′-(2,2′-oxybis(ethane-2,1-diyl)bis(3,5-dimethyl-1H-pyrazole); 2, NZN = bis[2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl]sulfane) in good yield. Compounds 1–2 were characterized by elemental analysis, multinuclear NMR spectroscopy, and X-ray structural analysis. Single crystal X-ray structural analyses indicate that the complexes are monomeric and the palladium center resides in a slightly distorted square planar environment. Furthermore, despite their intrinsic similarity, the NON and NSN ligands adopt different coordination modes around the palladium metal center. Additionally, the [PdCl2(NON)] (3) was shown to be an efficient catalyst precursor for the coupling of aryl bromides and iodides with arylboronic acids, esters and borate salts.

Graphical abstractThe reaction of (cod)Pd(Me)Cl with tridentate bis(pyrazolyl) ligands affords the alkyl-palladium(II) complexes [Pd(CH3)(NZN)][BF4] (1, NZN = bis[2-(3,5-dimethyl-l-pyrazolyl)ethyl]ether; 2, NZN = bis[2-(3,5-dimethyl-l-pyrazolyl)ethyl]sulfide) in good yield. In parallel, [PdCl2(NON)] (3) was shown to be an efficient catalyst precursor for the coupling of aryl bromides and iodides with arylboronic acids, esters and borate salts.Figure optionsDownload full-size imageDownload as PowerPoint slide