Preparation, Spectroscopic Characterization, and Reactivity of High-Valent Non-Oxo Co(IV) and Formally Co(V) Complexes

Jindou Yang; Virginia A. Larson; Daniel G. Castella; Devin F. Wilson; Ying Xing; Mi Sook Seo; Yong Min Lee; Ava Grace Slobin; Shunichi Fukuzumi; Jason Shearer; Nicolai Lehnert; Wonwoo Nam

doi:10.1021/jacsau.5c00589

Preparation, Spectroscopic Characterization, and Reactivity of High-Valent Non-Oxo Co(IV) and Formally Co(V) Complexes

Jindou Yang, Virginia A. Larson, Daniel G. Castella, Devin F. Wilson, Ying Xing, Mi Sook Seo, Yong Min Lee, Ava Grace Slobin, Shunichi Fukuzumi, Jason Shearer, Nicolai Lehnert, Wonwoo Nam

Department of Chemistry & Nanoscience

Research output: Contribution to journal › Article › peer-review

Abstract

In the presence of artificial oxidants, high-valent Co-X (X = O and NTs) complexes can be achieved in many different types of ligand structures. This paper reports, for the first time, the synthesis, spectroscopic and theoretical characterization, and reactivity of formally Co(V) and Co(IV) intermediates without the axial oxo or imido groups by using a strongly electron-donating ligand, PCAPD (PCAPD = bis[2-(1H-pyrrol-2-carboxamido)-o-phenylenediamine). The formally Co(V) complex was prepared by reacting [Et₄N]₂[Co^III(PCAPD)(Cl)] with iodosylbenzene (PhIO) as an artificial oxidant in acetone at −40 °C. Then, the formally Co(V) complex was characterized with various spectroscopic methods, such as EPR, CSI-MS, MCD, XAS, and EXAFS, revealing a diamagnetic [Co^IV(PCAPD^•+)(OH)₂]⁻species with a Co(IV) ion and one-electron oxidized coligand. Here, EXAFS shows a six-coordinate complex, likely with axial hydroxide ligands, but no oxo group with a short Co-X vector. This species can be further one-electron reduced by Me₂Fc to afford [Co^IV(PCAPD)(OH)₂]^2–in frozen conditions. EPR and MCD measurements show that [Co^IV(PCAPD)(OH)₂]^2–has an S = 1/2 ground state with a Co(IV) center according to XAS. EXAFS shows essentially identical ligand environments about the Co center in [Co^IV(PCAPD^•+)(OH)₂]⁻and [Co^IV(PCAPD)(OH)₂]^2–. Remarkably, the exact same high-valent species can be generated when [Et₄N]₂[Co^III(PCAPD)(Cl)] is oxidized with N-tosyliminophenyliodinane (PhINTs). The reactivity of [Co^IV(PCAPD^•+)(OH)₂]⁻was further investigated in hydrogen atom and oxygen atom transfer reactions, revealing that the reactivity of [Co^IV(PCAPD^•+)(OH)₂]⁻is much lower than that of other Co-X species.

Original language	English
Pages (from-to)	3575-3588
Number of pages	14
Journal	JACS Au
Volume	5
Issue number	7
DOIs	https://doi.org/10.1021/jacsau.5c00589
State	Published - 28 Jul 2025

Bibliographical note

Publisher Copyright:
© 2025 The Authors. Published by American Chemical Society

Keywords

O atom transfer
high-valent cobalt complexes
metal oxo complexes
noninnocent ligands
phenol oxidation
reactive intermediates
spectroscopy

Access to Document

10.1021/jacsau.5c00589

Cite this

@article{4a35de7347eb4907b1c9b1c9ebfee9c6,

title = "Preparation, Spectroscopic Characterization, and Reactivity of High-Valent Non-Oxo Co(IV) and Formally Co(V) Complexes",

abstract = "In the presence of artificial oxidants, high-valent Co-X (X = O and NTs) complexes can be achieved in many different types of ligand structures. This paper reports, for the first time, the synthesis, spectroscopic and theoretical characterization, and reactivity of formally Co(V) and Co(IV) intermediates without the axial oxo or imido groups by using a strongly electron-donating ligand, PCAPD (PCAPD = bis[2-(1H-pyrrol-2-carboxamido)-o-phenylenediamine). The formally Co(V) complex was prepared by reacting [Et4N]2[CoIII(PCAPD)(Cl)] with iodosylbenzene (PhIO) as an artificial oxidant in acetone at −40 °C. Then, the formally Co(V) complex was characterized with various spectroscopic methods, such as EPR, CSI-MS, MCD, XAS, and EXAFS, revealing a diamagnetic [CoIV(PCAPD•+)(OH)2]−species with a Co(IV) ion and one-electron oxidized coligand. Here, EXAFS shows a six-coordinate complex, likely with axial hydroxide ligands, but no oxo group with a short Co-X vector. This species can be further one-electron reduced by Me2Fc to afford [CoIV(PCAPD)(OH)2]2–in frozen conditions. EPR and MCD measurements show that [CoIV(PCAPD)(OH)2]2–has an S = 1/2 ground state with a Co(IV) center according to XAS. EXAFS shows essentially identical ligand environments about the Co center in [CoIV(PCAPD•+)(OH)2]−and [CoIV(PCAPD)(OH)2]2–. Remarkably, the exact same high-valent species can be generated when [Et4N]2[CoIII(PCAPD)(Cl)] is oxidized with N-tosyliminophenyliodinane (PhINTs). The reactivity of [CoIV(PCAPD•+)(OH)2]−was further investigated in hydrogen atom and oxygen atom transfer reactions, revealing that the reactivity of [CoIV(PCAPD•+)(OH)2]−is much lower than that of other Co-X species.",

keywords = "O atom transfer, high-valent cobalt complexes, metal oxo complexes, noninnocent ligands, phenol oxidation, reactive intermediates, spectroscopy",

author = "Jindou Yang and Larson, \{Virginia A.\} and Castella, \{Daniel G.\} and Wilson, \{Devin F.\} and Ying Xing and Seo, \{Mi Sook\} and Lee, \{Yong Min\} and Slobin, \{Ava Grace\} and Shunichi Fukuzumi and Jason Shearer and Nicolai Lehnert and Wonwoo Nam",

note = "Publisher Copyright: {\textcopyright} 2025 The Authors. Published by American Chemical Society",

year = "2025",

month = jul,

day = "28",

doi = "10.1021/jacsau.5c00589",

language = "English",

volume = "5",

pages = "3575--3588",

journal = "JACS Au",

issn = "2691-3704",

publisher = "American Chemical Society",

number = "7",

}

TY - JOUR

T1 - Preparation, Spectroscopic Characterization, and Reactivity of High-Valent Non-Oxo Co(IV) and Formally Co(V) Complexes

AU - Yang, Jindou

AU - Larson, Virginia A.

AU - Castella, Daniel G.

AU - Wilson, Devin F.

AU - Xing, Ying

AU - Seo, Mi Sook

AU - Lee, Yong Min

AU - Slobin, Ava Grace

AU - Fukuzumi, Shunichi

AU - Shearer, Jason

AU - Lehnert, Nicolai

AU - Nam, Wonwoo

PY - 2025/7/28

Y1 - 2025/7/28

N2 - In the presence of artificial oxidants, high-valent Co-X (X = O and NTs) complexes can be achieved in many different types of ligand structures. This paper reports, for the first time, the synthesis, spectroscopic and theoretical characterization, and reactivity of formally Co(V) and Co(IV) intermediates without the axial oxo or imido groups by using a strongly electron-donating ligand, PCAPD (PCAPD = bis[2-(1H-pyrrol-2-carboxamido)-o-phenylenediamine). The formally Co(V) complex was prepared by reacting [Et4N]2[CoIII(PCAPD)(Cl)] with iodosylbenzene (PhIO) as an artificial oxidant in acetone at −40 °C. Then, the formally Co(V) complex was characterized with various spectroscopic methods, such as EPR, CSI-MS, MCD, XAS, and EXAFS, revealing a diamagnetic [CoIV(PCAPD•+)(OH)2]−species with a Co(IV) ion and one-electron oxidized coligand. Here, EXAFS shows a six-coordinate complex, likely with axial hydroxide ligands, but no oxo group with a short Co-X vector. This species can be further one-electron reduced by Me2Fc to afford [CoIV(PCAPD)(OH)2]2–in frozen conditions. EPR and MCD measurements show that [CoIV(PCAPD)(OH)2]2–has an S = 1/2 ground state with a Co(IV) center according to XAS. EXAFS shows essentially identical ligand environments about the Co center in [CoIV(PCAPD•+)(OH)2]−and [CoIV(PCAPD)(OH)2]2–. Remarkably, the exact same high-valent species can be generated when [Et4N]2[CoIII(PCAPD)(Cl)] is oxidized with N-tosyliminophenyliodinane (PhINTs). The reactivity of [CoIV(PCAPD•+)(OH)2]−was further investigated in hydrogen atom and oxygen atom transfer reactions, revealing that the reactivity of [CoIV(PCAPD•+)(OH)2]−is much lower than that of other Co-X species.

AB - In the presence of artificial oxidants, high-valent Co-X (X = O and NTs) complexes can be achieved in many different types of ligand structures. This paper reports, for the first time, the synthesis, spectroscopic and theoretical characterization, and reactivity of formally Co(V) and Co(IV) intermediates without the axial oxo or imido groups by using a strongly electron-donating ligand, PCAPD (PCAPD = bis[2-(1H-pyrrol-2-carboxamido)-o-phenylenediamine). The formally Co(V) complex was prepared by reacting [Et4N]2[CoIII(PCAPD)(Cl)] with iodosylbenzene (PhIO) as an artificial oxidant in acetone at −40 °C. Then, the formally Co(V) complex was characterized with various spectroscopic methods, such as EPR, CSI-MS, MCD, XAS, and EXAFS, revealing a diamagnetic [CoIV(PCAPD•+)(OH)2]−species with a Co(IV) ion and one-electron oxidized coligand. Here, EXAFS shows a six-coordinate complex, likely with axial hydroxide ligands, but no oxo group with a short Co-X vector. This species can be further one-electron reduced by Me2Fc to afford [CoIV(PCAPD)(OH)2]2–in frozen conditions. EPR and MCD measurements show that [CoIV(PCAPD)(OH)2]2–has an S = 1/2 ground state with a Co(IV) center according to XAS. EXAFS shows essentially identical ligand environments about the Co center in [CoIV(PCAPD•+)(OH)2]−and [CoIV(PCAPD)(OH)2]2–. Remarkably, the exact same high-valent species can be generated when [Et4N]2[CoIII(PCAPD)(Cl)] is oxidized with N-tosyliminophenyliodinane (PhINTs). The reactivity of [CoIV(PCAPD•+)(OH)2]−was further investigated in hydrogen atom and oxygen atom transfer reactions, revealing that the reactivity of [CoIV(PCAPD•+)(OH)2]−is much lower than that of other Co-X species.

KW - O atom transfer

KW - high-valent cobalt complexes

KW - metal oxo complexes

KW - noninnocent ligands

KW - phenol oxidation

KW - reactive intermediates

KW - spectroscopy

UR - https://www.scopus.com/pages/publications/105014642627

U2 - 10.1021/jacsau.5c00589

DO - 10.1021/jacsau.5c00589

M3 - Article

AN - SCOPUS:105014642627

SN - 2691-3704

VL - 5

SP - 3575

EP - 3588

JO - JACS Au

JF - JACS Au

IS - 7

ER -

Preparation, Spectroscopic Characterization, and Reactivity of High-Valent Non-Oxo Co(IV) and Formally Co(V) Complexes

Abstract

Bibliographical note

Keywords

Access to Document

Fingerprint

Cite this