Synthesis of formazanate complexes with iridium and analysis of their spectroscopic and electrochemical properties



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ABSTRACT: Formazantes are a class of ligands that feature 1,2,4,5-tetraazapentadienyl core, with potential for variability in 3 out of the 5 positions. These complexes and their deriatives generally have notable visible absorption coupled with mild reduction potentials. These properties make these species suitable candidates for accessing new coordination complexes, featuring intriguing electronic and photophysical properties. These complexes have demonstrated the ability to bind numerous p-block metals and several first-row transition metals. Yet, the potential of these compounds as redox-active chelating ligands, esepcially with heavier transition metals remain underexplored. We have synthesized 9 novel complexes of di/triarylformazanate complexes with iridium by metathesis. The newly synthesized complexes include four cyclometalating ligands and five structurally modified triaryl and diarylformazanates. The compounds were characterized by UV-vis absorption spectroscopy and cyclic voltammetric techniques. An intense visible π → π* absorption, which is red shifted by over 100 nm relative to the free formazan ligands, were reported in metal formazanate complexes, and solvent-dependent electronic absorption spectra reveal some charge-transfer character in the HOMO → LUMO transition in Ir complexes. The formazanate-based reduction potential shifts as a result of electron donating or withdrawing groups. This behavior illustrates that the redox potentials could be manipulated by altering the substituents in the formazan backbone. Considering the simple synthetic pathways of these cyclometalated complexes, it is expected that exploration of these important ligand class will expand into other 3rd row metals. These explorations will likely result in new bindings and structural motifs involving formazante ligands and 3rd row transition metals.