Synthesis, crystal structures, and characterization of the complexes of the bulky ligand 2,6-bis-(3′,5′-diphenylpyrazolyl)pyridine with ruthenium, rhodium, and palladium

Abstract

Complexes of 2,6-bis-(3′,5′-diphenylpyrazolyl)pyridine (bdppp) with the chlorides of Ru(III), Pd(II), and Rh(III) have been synthesized. The X-ray structures of these complexes show that the ligand is tridentate and binds in a 1:1 ratio with the metal in all cases. The Ru and Rh complexes are octahedral, with one ligand and three chlorides around the metal, while the Pd complex is square planar, with one ligand and one chloride bound to the metal. The Pd complex features two Pd-bdppp complexes and a Pd2Cl62− counteranion. The electronic spectra of these complexes show strong UV absorbance bands from the phenyl rings present, with the Ru complex exhibiting several charge transfer bands and the Rh complex one charge transfer band. The 1H and 13C NMR spectra of the Rh and Pd complexes show slight differences from the free ligand, and the Ru complex is paramagnetic, featuring broad NMR peaks over a wide range. The Ru complex shows a quasi-reversible redox couple, while the Ru and Pd complexes show only irreversible reductions.