Azo-triazolide bis-cyclometalated Ir() complexes cyclization of 3-cyanodiarylformazanate ligands

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 49; no. 12; pp. 3775 - 3785
• Main Authors: Mu, Ge, Wen, Zhili, Wu, Judy I-Chia, Teets, Thomas S
• Format: Journal Article
• Language: English
• Published: 24.03.2020
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt03914g

In this work we describe the synthesis of sterically encumbered 1,5-diaryl-3-cyanoformazanate bis-cyclometalated iridium( iii ) complexes, two of which undergo redox-neutral cyclization during the reaction to produce carbon-bound 2-aryl-4-arylazo-2 H -1,2,3-triazolide ligands. This transformation offers a method for accessing 2-aryl-4-arylazo-2 H -1,2,3-triazolide ligands, a heretofore unreported class of chelating ligands. One formazanate complex and both triazolide complexes are structurally characterized by single-crystal X-ray diffraction, with infrared spectroscopy being the primary bulk technique to distinguish the formazanate and triazolide structures. All complexes are further characterized by UV-Vis absorption spectroscopy and cyclic voltammetry, with the triazolide compounds having similar frontier orbital energies to the formazanate complexes but much less visible absorption. Sterically encumbered iridium-bound formazanate ligands undergo redox-neutral cyclization to form azo-triazolides, a new class of redox-active chelating ligand.