Heteroleptic Complexes of Cyclometalated Platinum with Triarylformazanate Ligands

Formazanates are a ligand class featuring a 1,2,4,5-tetraazapentadienyl core, with variable substitution at the 1, 3, and 5 positions. Here we describe a set of four heteroleptic cylcometalated platinum complexes containing triarylformazanate ligands. The complexes are prepared by metathesis reactions of chloro-bridged dimers [Pt(C∧N)(μ-Cl)]2 (C∧N = 2-phenylpyridine or 2-(2,4-difluorophenyl)pyridine) with triarylformazans in the presence of base. X-ray diffraction studies reveal the molecular structures of three such complexes. Cyclic voltammograms and UV-vis absorption spectra of the complexes show features characteristic of both the cyclometalated platinum fragment and the formazanate, with the latter giving rise to two reversible one-electron reductions in the CV and an intense visible π → π* absorption which is red-shifted by >100 nm relative to the free formazan. The electronic structures and redox properties of the complexes were further investigated by UV-vis spectroelectrochemistry and density functional theory calculations. All of the experimental and theoretical work points to a frontier molecular orbital manifold where the formazanate π and π* orbitals are substantially mixed with d-orbitals derived from the platinum center.