Halide exchange studies of novel Pd(ii) NNN-pincer complexes

Palladium(ii) complexes with an NNN type pincer ligand (pip(2)NNN = 2,6-bis(piperdyl-methyl)pyridine) are synthesized and characterized. Electronic and (1)H NMR spectra point to decreasing filled/filled repulsions between the dπ(Pd) orbitals and the halide lone pair orbitals along the Cl < Br < I series. For all complexes, the most downfield α-piperidyl resonance of the pip(2)NNN ligand is sensitive to changes in the coordinated halide while the meta-pyridyl and benzylic resonances are sensitive to changes in the counter anion. This sensitivity is utilized to study halide association and exchange at the fourth coordination site. Conductivity and (1)H NMR spectroscopy confirm the interaction between the exogenous anion (Cl(−), Br(−), BF(4)(−)) and Pd(pip(2)NNN)X(+) (X = Cl, Br).