Metal chelates of conjugated ligands are of significant interest in inorganic research, especially for those bearing one or more π* orbitals lying low enough to promote properties like successive electron transfer, intense color and multiple oxidation and reduction states. The azo-imine chelating system exhibits such unique features but it is not fully explored. This is due to the difficulties in synthesis and the fact that the azo-imine system is only formed and stabilized in the chelated state. Expanding on previous methods, which involve proton-coupled reduction of azo-oxime chelates, we synthesized the first examples of homoleptic platinum azo-iminate complexes by treating triarylformazans with Pt(DMSO)<sub>2</sub>Cl<sub>2</sub> under reducing conditions. The transformation represents a three-proton, three-electron reduction of each formazan and offers a new route for accessing this class of redox-active ligands. The reaction is general for triarylformazans with both electron-donating and electron-withdrawing substitutents, and four complexes in total are described. X-ray crystal structures of all four complexes are obtained, and are consistent with an electronic structure consisting of a formal Pt(II) center where each azo-iminate is in a monoanionic radical form and contributes five π electrons. The complexes are all diamagnetic, indicating delocalization of the π system over both ligands. The complexes are further characterized by cyclic voltammetry and UV-Vis absorption spectroscopy, which indicate ligand-centered redox chemistry and strong visible absorption.

Homoleptic platinum azo-iminate complexes via hydrogenative cleavage of formazans

255th National Meeting (2018)

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