Palladium(II) and platinum(II) complexes bearing a kappa(SCS)-S-3 pincer ligand with an azulene unit

Novel Pd and Pt SCS-pincer complexes with an azulene unit were synthesized from the reaction of a metal precursor with an azulene molecule having two thioamide moieties. The crystal structures of the complexes were confirmed by X-ray diffraction analysis. Their structural and optical properties were investigated in comparison with those of related complexes with a benzene and pyrrole unit by NMR and UV/Vis spectroscopy. DFT calculations for the azulene complexes revealed that the origin of the long-wavelength absorption is assigned to a transition from the metal center to the extended p system of the azulene unit.