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).