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

Abstract

Palladium(II) complexes with an NNN type pincer ligand (pip₂NNN = 2,6-bis(piperdyl-methyl)pyridine) are synthesized and characterized. Electronic and ¹H 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 pip₂NNN 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 ¹H NMR spectroscopy confirm the interaction between the exogenous anion (Cl⁻, Br⁻, BF₄⁻) and Pd(pip₂NNN)X⁺ (X = Cl, Br).