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Preparation, Spectroscopic Characterization, and Reactivity of High-Valent Non-Oxo Co(IV) and Formally Co(V)
Jindou Yang1, Virginia A Larson2, Daniel G Castella2
1Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea.
JACS Au
|August 1, 2025
Summary
This study synthesizes novel high-valent cobalt complexes, Co(IV), using a unique electron-donating ligand, PCAPD. These complexes, lacking axial oxo groups, exhibit distinct reactivity in oxidation reactions.
Area of Science:
- Inorganic Chemistry
- Organometallic Chemistry
- Spectroscopy
Background:
- High-valent cobalt-oxo and cobalt-imido complexes are typically formed using artificial oxidants.
- Achieving high-valent cobalt species without axial oxo or imido ligands presents a synthetic challenge.
Purpose of the Study:
- To synthesize and characterize novel high-valent cobalt intermediates without axial oxo or imido groups.
- To investigate the electronic structure and reactivity of these unique cobalt species.
Main Methods:
- Synthesis of cobalt complexes using a strongly electron-donating ligand, PCAPD (bis-[2-(1H-pyrrol-2-carboxamido)-o-phenylenediamine]).
- Oxidation of a Co(III) precursor with artificial oxidants like iodosylbenzene (PhIO) and N-tosyliminophenyliodinane (PhINTs).
- Characterization using spectroscopic techniques including EPR, CSI-MS, MCD, XAS, and EXAFS, alongside theoretical calculations.
Main Results:
- Successful synthesis of formally Co(V) and Co(IV) intermediates, [CoIV(PCAPD•+)-(OH)2]- and [CoIV(PCAPD)-(OH)2]2-.
- Spectroscopic and EXAFS data reveal a six-coordinate Co(IV) center with axial hydroxide ligands and a one-electron oxidized coligand, notably lacking oxo groups.
- These high-valent species exhibit significantly lower reactivity in hydrogen atom and oxygen atom transfer reactions compared to other cobalt complexes.
Conclusions:
- This work reports the first synthesis of high-valent cobalt complexes (formally Co(V) and Co(IV)) without axial oxo or imido ligands.
- The characterized species, [CoIV(PCAPD•+)-(OH)2]- and [CoIV(PCAPD)-(OH)2]2-, possess unique electronic structures and reduced reactivity.
- The findings expand the understanding of cobalt oxidation states and their associated ligand environments.
Keywords:
O atom transferhigh-valent cobalt complexesmetal oxo complexesnoninnocent ligandsphenol oxidationreactive intermediatesspectroscopyMore Related Videos
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