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

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

doi:10.1021/acs.organomet.3c00100

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

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

^*Corresponding author for this work

Department of Chemistry

Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review

2 Citations (Scopus)

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] (NaL_OEt) afforded [H₃dtpny][Ir(Bubnpy)(CO)Cl₂] (2), [Ir(Bubnpy)(CNxyl)₂Cl] (3), [Ir(Bubnpy)(PCy₃)Cl] (4), and [Ir(Bubnpy)(L_OEt)] (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(L_OEt)(N)Cl₂] afforded the respective heterometallic μ-nitrido complexes [(H₂O)Cl(Bubnpy)Ir(μ-N)Ru(L_OEt)Cl₂] (7) and [(PCy₃)Cl(Bubnpy)Ir(μ-N)Ru(L_OEt)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 g_x = 2.06, g_y = 1.91, and g_z = 2.84 and Ir(IV) (I = 3/2) hyperfine coupling constants A_xx, A_yy, and A_zz 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(L_OEt)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.

Original language	English
Pages (from-to)	719–731
Journal	Organometallics
Volume	42
Issue number	8
Online published	7 Apr 2023
DOIs	https://doi.org/10.1021/acs.organomet.3c00100
Publication status	Published - 24 Apr 2023

Funding

Support from The Hong Kong Research Grants Council (Project Nos. 16301019, 16201120, and 16301621) and the Hong Kong University of Science and Technology is gratefully acknowledged.

Access Output

10.1021/acs.organomet.3c00100

Other Access Options

Check CityUHK Library

Permanent Link

Right click to copy link

Cite this

@article{a827a76926234a1dae6971114725e3c6,

title = "High-Valent Iridium Complexes Containing a Tripodal Bis-Cyclometalated C^N^C Ligand",

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 Kl{\"a}ui 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) {\AA}] and Ru-N [1.661(5) {\AA}] 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. {\textcopyright} 2023 American Chemical Society.",

author = "Rain Ng and Shun-Cheung Cheng and Ka-Lok Chan and Cheuk-Pui Leung and Wai-Man Cheung and Sung, {Herman H.-Y.} and Lee, {Hung Kay} and Chi-Chiu Ko and Williams, {Ian D.} and Zhenyang Lin and Wa-Hung Leung",

year = "2023",

month = apr,

day = "24",

doi = "10.1021/acs.organomet.3c00100",

language = "English",

volume = "42",

pages = "719–731",

journal = "Organometallics",

issn = "0276-7333",

publisher = "American Chemical Society",

number = "8",

}

TY - JOUR

T1 - High-Valent Iridium Complexes Containing a Tripodal Bis-Cyclometalated C^N^C Ligand

AU - Ng, Rain

AU - Cheng, Shun-Cheung

AU - Chan, Ka-Lok

AU - Leung, Cheuk-Pui

AU - Cheung, Wai-Man

AU - Sung, Herman H.-Y.

AU - Lee, Hung Kay

AU - Ko, Chi-Chiu

AU - Williams, Ian D.

AU - Lin, Zhenyang

AU - Leung, Wa-Hung

PY - 2023/4/24

Y1 - 2023/4/24

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85152128837&partnerID=8YFLogxK

UR - https://www.scopus.com/record/pubmetrics.uri?eid=2-s2.0-85152128837&origin=recordpage

U2 - 10.1021/acs.organomet.3c00100

DO - 10.1021/acs.organomet.3c00100

M3 - RGC 21 - Publication in refereed journal

SN - 0276-7333

VL - 42

SP - 719

EP - 731

JO - Organometallics

JF - Organometallics

IS - 8

ER -

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

Abstract

Funding

Access Output

Other Access Options

Permanent Link

Other Files and Links

Fingerprint

Cite this