Unusual coordination of a 1,2,3-triazolyl-pyridine ligand in a Pd(II) complex: application in the Suzuki-Miyaura coupling reaction

A modified "click" reaction between 2-azidopyridine and di(prop-2-yn-1-yl)phthalate [dpp] (2) produces a novel bis(1,2,3-triazolyl-pyridine) ligand on an ortho-phthalic acid platform [bptmp] (3). The [bptmp] ligand is prepared to produce transition metal complexes through selective N-3 coordination of the inverse triazolyl-pyridine ligand. An equimolar reaction between [bptmp] (3) and PdCl2(CH3CN)(2) in acetonitrile leads to the isolation of a light-yellow solid (4). Several spectroscopic and spectrometry data established that the formed complex has a molecular formula of PdCl2[bptmp] (4). Molecular structure determination using a single crystal X-ray diffraction study further established the formation of a 1 : 1 metal-ligand complex, where PdCl2 bridges the two side-arms of the phthalic acid platform. As per the design of [bptmp], in complex (4), the chelating bidentate triazolyl-pyridine units are not coordinated, whereas the N-3 nitrogen of the inverse triazolyl-pyridine selectively coordinated to Pd(ii). Furthermore, complex (4) is proved to be a highly effective catalyst for the Suzuki-Miyaura coupling reaction in a water/ethanol solvent combination with very modest catalyst loading. The high reactivity of complex 4 in the catalytic Suzuki-Miyaura coupling reaction is attributed to the electronic and steric properties of the [bptmp] ligand.