Synthesis and Isolation of an Anionic Bis(dipyrido-annulated) N-Heterocyclic Carbene CCC-Pincer Iridium(III) Complex by Facile C-H Bond Activation

Kazuki Nakanishi; J Oscar C Jimenez-Halla; Seiji Yamazoe; Masaaki Nakamoto; Rong Shang; Yohsuke Yamamoto

doi:10.1021/acs.inorgchem.1c01236

Synthesis and Isolation of an Anionic Bis(dipyrido-annulated) N-Heterocyclic Carbene CCC-Pincer Iridium(III) Complex by Facile C-H Bond Activation

Inorg Chem. 2021 Jul 5;60(13):9970-9976. doi: 10.1021/acs.inorgchem.1c01236. Epub 2021 Jun 22.

Authors

Kazuki Nakanishi¹, J Oscar C Jimenez-Halla², Seiji Yamazoe³, Masaaki Nakamoto¹, Rong Shang¹, Yohsuke Yamamoto¹

Affiliations

¹ Department of Chemistry, Graduate School of Advanced Science and Engineering, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
² Department of Chemistry, Division of Natural and Exact Sciences, University of Guanajuato, Campus Gto, Noria Alta s/n, 36050 Guanajuato, Mexico.
³ Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.

PMID: 34156239
DOI: 10.1021/acs.inorgchem.1c01236

Abstract

Meridional tridentate N-heterocyclic carbene (NHC)-based pincer ligands contribute to a substantial growth in modern organometallic chemistry in both homogeneous catalysis and luminescence materials. Among all NHC-based pincer ligands, the dianionic LX₂-type CCC-pincer ones constitute the smallest subcategory owing to their limited ligand frameworks suitable for complexation. This work reports a one-pot, high-yield synthesis of a homoleptic anionic all-carbon bis-pincer iridium(III) complex (4) directly from a bis(aryl)-substituted dipyrido-annulated (dpa^Ar2) imidazolium salt and [Ir(COD)Cl]₂ via a cascade of deprotonation/C-H activation processes. Both experimental complexation chemistry and computational mechanistic investigation suggest that the large bite angle and π-rich character of the dpa^Ar2 NHC are responsible for its facile complexation as a dianionic LX₂-type CCC-pincer ligand precursor. The all-carbon ligated iridium(III) complex (4) bearing a π-conjugated ligand scaffold showed remarkably low oxidation potentials, which allows future investigations in its redox chemistry and photophysical properties.