106-fold faster C-H bond hydroxylation by a CoIII,IV2(µ-O)2 complex [via a CoIII2(µ-O)(µ-OH) intermediate] versus its FeIIIFeIV analog

Synthesis and Reactivity of a Non-Heme μ-Oxodicobalt(IV) Complex

A mononuclear CoIII complex (1) of a bisamide-bisalkoxide donor ligand was synthesized and thoroughly characterized. The reaction of 1 with 0.5 equiv. of m-chloroperbenzoic acid (m-CPBA) in acetonitrile at -40 °C resulted in the formation of a μ-oxodicobalt(IV) complex (2), which was characterized by an array of spectroscopic techniques, including X-ray absorption spectroscopy which revealed a short Co-Ooxo distance of 1.67 Å. Reactivity studies of 2 towards oxidation/oxygenation of hydrocarbon C-H bond and triphenylphosphine or thioanisole derivatives have been examined. UV-vis spectroscopy studies showed the appearance of clear isosbestic points during the oxidation of substrates together with a neat transformation of 2 to 1. Detailed kinetic investigations established that 2 follows a Concerted Proton-Electron Transfer (CPET) mechanism for hydrocarbon oxidation and has a weak electrophilic character. Catalytic behavior of 1 was noted towards the oxygen atom transfer reactions. This study showcases the spectroscopic investigation and reactivity studies of a CoIV(μ-O)CoIV moiety. Although the FeIV analog of such a core has been described before, the study describes the first example with a CoIV center.

Structural and reactivity insights into high-valent Co(III)-(μ-peroxo)-Co(IV) and its electromer Co(III)-(μ-superoxo)-Co(III)

Various metalloenzymes employ O2 for oxidative reactions, which is crucial in catalysis and biological processes involving high-valent metal-oxygen species. This study introduces novel high-valent Co(III)-(μ-1,2-O2)-Co(IV) and Co(III)-(μ-1,2-O2˙-)-Co(III) complexes, stabilized by an electron-donating TPA* ligand. This study advances our understanding of Co-oxygen intermediates, which are key for water oxidation catalysis.

Isolation and Crystallographic Characterization of an Octavalent Co2O2 Diamond Core

High-valent cobalt oxides play a pivotal role in alternative energy technology as catalysts for water splitting and as cathodes in lithium-ion batteries. Despite this importance, the properties governing the stability of high-valent cobalt oxides and specifically possible oxygen evolution pathways are not clear. One root of this limited understanding is the scarcity of high-valent Co(IV)-containing model complexes; there are no reports of stable, well-defined complexes with multiple Co(IV) centers. Here, an oxidatively robust fluorinated ligand scaffold enables the isolation and crystallographic characterization of a Co(IV)2-bis-μ-oxo complex. This complex is remarkably stable, in stark contrast with previously reported Co(IV)2 species that are highly reactive, which demonstrates that oxy-Co(IV)2 species are not necessarily unstable with respect to oxygen evolution. This example underscores a new design strategy for highly oxidizing transition-metal fragments and provides detailed data on a previously inaccessible chemical unit of relevance to O-O bond formation and oxygen evolution.

A Co(III)-peroxo-arylboronate complex formed by nucleophilic reaction of a Co(III)-peroxo species

In this work, we report the generation and characterization of two new Co(III)-peroxo complexes 2 and 3. 2 is best described as a mononuclear CoIII-(O2) complex that exhibits an 18O-isotope sensitive OO bond stretching vibration at 845(-49) cm-1, indicating a relatively weak peroxo moiety compared to those of other CoIII-(O2) complexes reported previously. Complex 3 is a CoIII-peroxo-arylboronate species having a rare {CoIIIOOBO} five-membered metallocycle, which is structurally characterized using X-ray crystallography. Investigations of the reaction mechanism using density functional theory calculations show that 2 likely undergoes a nucleophilic attack to an arylboronic acid, which is generated by hydrolysis of the BPh4- anion in wet acetonitrile solution, to first form a CoIII-peroxo-arylboronic acid adduct, followed by the loss of one benzene molecule to generate the five-membered metallocycle. The entire reaction is thermodynamically favorable. Taken together, the conversion of 2 to 3 represents the discovery of a novel nucleophilic reactivity that can be carried out by mononuclear Co(III)-peroxo complexes.