Single-step benzene hydroxylation by cobalt(<scp>ii</scp>) catalysts <i>via</i> a cobalt(<scp>iii</scp>)-hydroperoxo intermediate

Anandababu, Karunanithi; Muthuramalingam, Sethuraman; Velusamy, Marappan; Mayilmurugan, Ramasamy

doi:10.1039/c9cy02601k

Cited by 20 publications

(30 citation statements)

References 44 publications

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“…In addition, recently reported nickel, copper and cobalt complexes supported by aminopyridine ligands accomplished the oxidation of benzene to phenol in improved yields (29–41%) (Figure 1). [4e–g] …”

Section: Introductionmentioning

confidence: 99%

Aromatic C−H Hydroxylation Reactions with Hydrogen Peroxide Catalyzed by Bulky Manganese Complexes

et al. 2021

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The oxidation of aromatic substrates to phenols with H2O2 as a benign oxidant remains an ongoing challenge in synthetic chemistry. Herein, we successfully achieved to catalyze aromatic C−H bond oxidations using a series of biologically inspired manganese catalysts in fluorinated alcohol solvents. While introduction of bulky substituents into the ligand structure of the catalyst favors aromatic C−H oxidations in alkylbenzenes, oxidation occurs at the benzylic position with ligands bearing electron‐rich substituents. Therefore, the nature of the ligand is key in controlling the chemoselectivity of these Mn‐catalyzed C−H oxidations. We show that introduction of bulky groups into the ligand prevents catalyst inhibition through phenolate‐binding, consequently providing higher catalytic turnover numbers for phenol formation. Furthermore, employing halogenated carboxylic acids in the presence of bulky catalysts provides enhanced catalytic activities, which can be attributed to their low pKa values that reduces catalyst inhibition by phenolate protonation as well as to their electron‐withdrawing character that makes the manganese oxo species a more electrophilic oxidant. Moreover, to the best of our knowledge, the new system can accomplish the oxidation of alkylbenzenes with the highest yields so far reported for homogeneous arene hydroxylation catalysts. Overall our data provide a proof‐of‐concept of how Mn(II)/H2O2/RCO2H oxidation systems are easily tunable by means of the solvent, carboxylic acid additive, and steric demand of the ligand. The chemo‐ and site‐selectivity patterns of the current system, a negligible KIE, the observation of an NIH‐shift, and the effectiveness of using tBuOOH as oxidant overall suggest that hydroxylation of aromatic C−H bonds proceeds through a metal‐based mechanism, with no significant involvement of hydroxyl radicals, and via an arene oxide intermediate.

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Section: Introductionmentioning

confidence: 99%

Aromatic C−H Hydroxylation Reactions with Hydrogen Peroxide Catalyzed by Bulky Manganese Complexes

et al. 2021

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“…Pyridylethylation of amines has previously been used to prepare a variety of chelating agents (Phillip et al, 1970;Profft & Georgi, 1961;Profft & Lojack 1962;Gray et al, 1960;Kryatov et al, 2002;Kryatova et al, 2012;Marsich et al, 1998;Karlin et al, 1984;Anandababu et al, 2020;Muthuramalingam et al, 2019a,b), with an original driver being the generation of biomimetic molecules (Karlin et al, 1984). Examples immediately relevant to the present work (Fig.…”

Section: Chemical Contextmentioning

confidence: 96%

“…Closely related compounds with similar (Anandababu et al, 2020) and Cu(Dpzp)(NCÁNÁCN)-ClO 4 (Mautner et al, 2008).…”

Section: Database Surveymentioning

confidence: 99%

“…In the case of Phpz, there are reports of copper(II) complexes (O'Connor et al, 2012), including their application as oxidation catalysts (Muthuramalingam et al, 2017(Muthuramalingam et al, , 2020. In addition, nickel(II) complexes of Phpz have been studied as catalysts (Muthuramalingam et al, 2019a,b) as has a recent cobalt(II) complex (Anandababu et al, 2020). For Pmhpz, copper and nickel complexes have been characterized (O'Connor et al, 2012), and Muthuramalingam and coworkers have recently examined oxidative catalysis by copper complexes including that of Pmhpz (Muthuramalingam et al, 2021), but there appears to be only the single prior report of Pdmpz (O'Connor et al, 2012).…”

Section: Chemical Contextmentioning

confidence: 99%

“…The core geometry is markedly toward the trigonal-bipyramidal ( = 0.62) (Addison et al, 1984) 167.11 (18) the piperazine nitrogen atom (N3) holding the dangling arm is 0.08 (3) A ˚longer than the one associated with the coordinated pyridine arm. Inasmuch as the ability of Phpz to act as a tetradentate toward Co II has recently been demonstrated in [Co(Phpz)Cl](BPh 4 ) (Anandababu et al, 2020), it is clear that ligand bite is not the sole factor governing the structural outcome in Co(Phpz)Cl 2 . However, all the complexes herein were prepared in non-aqueous solvents -methanol or THFand we propose that the chloride ion, with its substantial hydration energy, is solvofugic enough to displace a terminal pyridine in a complex involving cobalt(II).…”

Section: Structural Commentarymentioning

confidence: 99%

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Chlorocobalt complexes with pyridylethyl-derived diazacycloalkanes

Addison¹,

Jaworski²,

Jasinski³

et al. 2022

Acta Cryst E

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Syntheses are described for the blue/purple complexes of cobalt(II) chloride with the tetradentate ligands 1,4-bis[2-(pyridin-2-yl)ethyl]piperazine (Ppz), 1,4-bis[2-(pyridin-2-yl)ethyl]homopiperazine (Phpz), trans-2,5-dimethyl-1,4-bis[2-(pyridin-2-yl)ethyl]piperazine (Pdmpz) and tridentate 4-methyl-1-[2-(pyridin-2-yl)ethyl]homopiperazine (Pmhpz). The CoCl2 complexes with Ppz, namely, {μ-1,4-bis[2-(pyridin-2-yl)ethyl]piperazine}bis[dichloridocobalt(II)], [Co2Cl4(C18H24N4)] or Co2(Ppz)Cl4, and Pdmpz (structure not reported as X-ray quality crystals were not obtained), are shown to be dinuclear, with the ligands bridging the two tetrahedrally coordinated CoCl2 units. Co2(Ppz)Cl4 and {dichlorido{4-methyl-1-[2-(pyridin-2-yl)ethyl]-1,4-diazacycloheptane}cobalt(II) [CoCl2(C13H21N3)] or Co(Pmhpz)Cl2, crystallize in the monoclinic space group P21/n, while crystals of the pentacoordinate monochloro chelate 1,4-bis[2-(pyridin-2-yl)ethyl]piperazine}chloridocobalt(II) perchlorate, [CoCl(C18H24N4)]ClO4 or [Co(Ppz)Cl]ClO4, are also monoclinic (P21). The complex {1,4-bis[2-(pyridin-2-yl)ethyl]-1,4-diazacycloheptane}dichloridocobalt(II) [CoCl2(C19H26N4)] or Co(Phpz)Cl2 (P\overline{1}) is mononuclear, with a pentacoordinated CoII ion, and entails a Phpz ligand acting in a tridentate fashion, with one of the pyridyl moieties dangling and non-coordinated; its displacement by Cl− is attributed to the solvophobicity of Cl− toward MeOH. The pentacoordinate Co atoms in Co(Phpz)Cl2, [Co(Ppz)Cl]+ and Co(Pmhpz)Cl2 have substantial trigonal–bipyramidal character in their stereochemistry. Visible- and near-infrared-region electronic spectra are used to differentiate the two types of coordination spheres. TDDFT calculations suggest that the visible/NIR region transitions contain contributions from MLCT and LMCT character, as well as their expected d–d nature. For Co(Pmhpz)Cl2 and Co(Phpz)Cl2, variable-temperature magnetic susceptibility data were obtained, and the observed decreases in moment with decreasing temperature were modelled with a zero-field-splitting approach, the D values being +28 and +39 cm−1, respectively, with the S = 1/2 state at lower energy.

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Recent Achievements in Organic Reactions in MeCN

Xing,

Zhai,

et al. 2024

Green Solvents in Organic Synthesis

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Single-step benzene hydroxylation by cobalt(ii) catalysts via a cobalt(iii)-hydroperoxo intermediate

Abstract: Cobalt(ii) complexes reported as efficient and selective catalysts for single-step phenol formation from benzene using H2O2. The catalysis proceeds likely via cobalt(iii)-hydroperoxo species.

Cited by 20 publications

References 44 publications

Aromatic C−H Hydroxylation Reactions with Hydrogen Peroxide Catalyzed by Bulky Manganese Complexes

Aromatic C−H Hydroxylation Reactions with Hydrogen Peroxide Catalyzed by Bulky Manganese Complexes

Chlorocobalt complexes with pyridylethyl-derived diazacycloalkanes

Recent Achievements in Organic Reactions in MeCN

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