Redox Activity of IrIII Complexes with Multidentate Ligands Based on Dipyrido-annulated N-Heterocyclic Carbenes: Access to High Valent and High Spin State with Carbon Donors

K. Nakanishi, L.I. Lugo-Fuentes, J. Manabe, R. Guo, S. Kikkawa, S. Yamazoe, K. Komaguchi, S. Kume, D.W. Szczepanik, M. Solà, J.O.C. Jimenez-Halla, S. Nishihara, K. Kubo, M. Nakamoto, Y. Yamamoto, T. Mizuta, R. Shang

Chem. A Euro. J., in press.

Synthetic strategies to access high-valent iridium complexes usually require use of π donating ligands bearing electronegative atoms (e.g. amide or oxide) or s donating electropositive atoms (e.g. boryl or hydride). Besides the h5 - (methyl)cyclopentadienyl derivatives, high-valent h1 carbon-ligated iridium complexes are challenging to synthesize. To meet this challenge, this work reports the oxidation behavior of an all-carbonligated anionic bis(CCC-pincer) IrIII complex. Being both s and π donating, the diaryl dipyrido-annulated N-heterocyclic carbene (dpa-NHC) IrIII complex allowed a stepwise 4e– oxidation sequence. The first 2e– oxidation led to an oxidative coupling of two adjacent aryl groups, resulting in formation of a cationic chiral IrIII complex bearing a CCCC-tetradentate ligand. A further 2e– oxidation allowed isolation of a high-valent tricationic complex with a triplet ground state. These results close a synthetic gap for carbon-ligated iridium complexes and demonstrate the electronic tuning potential of organic π ligands for unusual electronic properties.