Homoleptic Platinum Azo-iminate Complexes via Hydrogenative Cleavage of Formazans.

Homoleptic platinum azo-iminate complexes are formed when triarylformazans are treated with Pt(DMSO)2Cl2 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 substituents, and four complexes in total are described. X-ray crystal structures of all four complexes are presented 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, which shows multiple ligand-centered redox events, including proton-coupled oxidation waves. UV-vis spectroelectrochemistry provides further insight into the nature of the redox events. UV-vis absorption spectroscopy shows strong visible absorption bands attributed to HOMO → LUMO transitions, which is corroborated by time-dependent DFT computations on representative examples.