Formazan ligands, which are nitrogen-rich analogues of β-diketiminates, generally have notable visible absorption coupled with accessible reduction potentials, making them a good candidate for accessing new coordination complexes with intriguing electronic properties. Transition metal complexes of formazan ligands have garnered significant interest in last few years because of their spectroscopic and electrochemical properties. Complexes of formazans with first row transition metals, palladium, cobalt, zinc, and boron were reported along with the elaborate explanation of their redox and optical properties. But there were very few examples of formazan ligands coordinated to third row transition metals. In this work, a series of di/triarylformazanate cyclometalated complexes with platinum (II) and iridium (III) is described, where unique redox and photophysical properties are observed by combining third-row transition metals with formazanate ligands. X-ray crystallography reveals the molecular structure of several Pt/Ir formazanate complexes. An intense visible π → π* absorption, which is red shifted by &gt;100 nm relative to the free formazan ligands, is observed in both types of metal formazanate complexes. Solvent-dependent electronic absorption spectra reveal some charge-transfer character in the HOMO → LUMO transition in Pt(II) formazanate complexes. Pt formazanate complexes can be electrochemically reduced via two or three one-electron reductions, with the redox potentials controlled by altering the presence of electron-withdrawing or -donating substituents in the formazan backbone. The easy synthetic routes to prepare these metal complexes provides opportunities to expand the coordination chemistry of this important ligand class to other third row metals, to discover new binding modes and structural motifs involving formazanate ligands and heavy transition metals; and to demonstrate the effect of metal d-orbital mixing on the formazanate-derived redox and optical properties.

Synthesis of formazanate complexes with third row transition metals and analysis of their spectroscopic and electrochemical properties

255th National Meeting (2018)

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