Homoleptic Platinum Azo-Iminate Complexes Via Hydrogenative Cleavage Of Formazans

Homoleptic platinum azo-iminate complexes are formed when triarylformazans are treated with Pt(DMSO)(2)Cl-2 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 pi electrons. The complexes are all diamagnetic, indicating delocalization of the pi 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.