High-Valent Iridium Complexes Containing a Tripodal Bis-Cyclometalated C^N^C Ligand

Research output: Journal Publications and ReviewsRGC 21 - Publication in refereed journalpeer-review

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Author(s)

  • Rain Ng
  • Shun-Cheung Cheng
  • Ka-Lok Chan
  • Cheuk-Pui Leung
  • Wai-Man Cheung
  • Herman H.-Y. Sung
  • Hung Kay Lee
  • Ian D. Williams
  • Zhenyang Lin
  • Wa-Hung Leung

Related Research Unit(s)

Detail(s)

Original languageEnglish
Pages (from-to)719–731
Journal / PublicationOrganometallics
Volume42
Issue number8
Online published7 Apr 2023
Publication statusPublished - 24 Apr 2023

Abstract

Iridium complexes containing a bis-cyclometalated tripodal C^N^C ligand have been synthesized, and their redox property and reactivity have been studied. The previously reported intermediate (1) prepared from IrCl3·xH2O and bis(4-(tert-butyl)phenyl)methyl)pyridine (H2Bubnpy) has been used as a starting material for synthesis of Ir(C^N^C) complexes. Treatment of 1 with CO, xylNC (xyl = 2,6-dimethylphenyl), PCy3 (Cy = cyclohexyl), and the Kläui tripodal ligand Na[Co(η5-C5H5){P(O)(OEt)2}3] (NaLOEt) afforded [H3dtpny][Ir(Bubnpy)(CO)Cl2] (2), [Ir(Bubnpy)(CNxyl)2Cl] (3), [Ir(Bubnpy)(PCy3)Cl] (4), and [Ir(Bubnpy)(LOEt)] (6), respectively. Reaction of 5-coordinated 4 with CO gave the adduct [Ir(Bubnpy)(PCy3)Cl(CO)] (5). Treatment of 1 and 4 with [Ru(LOEt)(N)Cl2] afforded the respective heterometallic μ-nitrido complexes [(H2O)Cl(Bubnpy)Ir(μ-N)Ru(LOEt)Cl2] (7) and [(PCy3)Cl(Bubnpy)Ir(μ-N)Ru(LOEt)Cl2] (8). The Ir-N [1.887(5) Å] and Ru-N [1.661(5) Å] distances in 7 are indicative of the Ir(V)═N═Ru(IV) resonance structure. The cyclic voltammogram of 6 in CH2Cl2 displayed a reversible couple at ca. 0 V vs Fc+/0 (Fc = ferrocene) that is assigned as the Ir(IV/III) couple. Oxidation of 6 with Ag(OTf) (OTf- = triflate) afforded 6·OTf that exhibited an EPR signal in CH2Cl2 at 4 K with gx = 2.06, gy = 1.91, and gz = 2.84 and Ir(IV) (I = 3/2) hyperfine coupling constants Axx, Ayy, and Azz of 60, 40, and 18 G, respectively, consistent with the Ir(IV) formulation. Treatment of 4 with PhICl2 yielded [Ir(Bubnpy)(PCy3)Cl2] (9), whereas the reaction of 7 with PhICl2 yielded mixed-valence [Cl2(Cl2Bubnpy)Ir(μ-N)Ru(LOEt)Cl2] (10) that contains a chlorinated C^N^C ligand. DFT calculations indicated that the spin density in 10 is mostly found at the Ir atom, the chloride ligands, and a phenyl ring of the C^N^C ligand. 1 and 4 can catalyze the oxidation of cyclooctene with PhIO, possibly via an Ir-oxo or Ir-PhIO active intermediate. The results of this work highlight the ability of the dianionic tripodal C^N^C ligand to stabilize high-valent iridium. © 2023 American Chemical Society.

Citation Format(s)

High-Valent Iridium Complexes Containing a Tripodal Bis-Cyclometalated C^N^C Ligand. / Ng, Rain; Cheng, Shun-Cheung; Chan, Ka-Lok et al.
In: Organometallics, Vol. 42, No. 8, 24.04.2023, p. 719–731.

Research output: Journal Publications and ReviewsRGC 21 - Publication in refereed journalpeer-review