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.