One step phenol synthesis from benzene catalysed by nickel(<scp>ii</scp>) complexes

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

doi:10.1039/c9cy01471c

Cited by 26 publications

(37 citation statements)

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“…Toluene was oxidized to para ‐cresol in 22% yield, together with ortho ‐cresol and methyl‐ para ‐benzoquinone in 8 and 1% yield, respectively (Table 3, entry 3). Recent studies on aromatic oxidations have shown other complexes to be capable of oxidizing the aromatic ring of toluene as well, showing however significant amounts of aliphatic oxidation towards benzyl alcohol or benzaldehyde products [3g,4a,b,e,f] . Remarkably, Mn( tips bpmcn) shows an excellent selectivity for oxidation of the aromatic ring over the aliphatic site chain.…”

Section: Resultsmentioning

confidence: 99%

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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: Resultsmentioning

confidence: 99%

“…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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“…Therefore, it is extremely essential to adopt suitable methods for the industrial manufacture of phenol, which should preferably defeat the shortcomings of the cumene process. − Therefore, direct benzene hydroxylation is one of the most efficient ways to produce phenol with a better atom economy. This process mostly occurs via the activation of one of the C–H bonds; however, its higher bond energy (460 kJ mol –1 ) makes that difficult. − In recent years, many researchers are thoughtfully exploring the possibility of an efficient methodology by designing new catalysts that are able to perform selective phenol synthesis in a single step from benzene and greener oxidants like O 2 or activated oxygen sources . The efforts through conventional approaches like electrochemical oxidation, photochemical oxidation, and Fenton-type reaction are reported to afford lower yields of phenol with poor selectivity.…”

Section: Introductionmentioning

confidence: 99%

Benzene Hydroxylation by Bioinspired Copper(II) Complexes: Coordination Geometry versus Reactivity

et al. 2020

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A series of bioinspired copper(II) complexes of N 4 -tripodal and sterically crowded diazepane-based ligands have been investigated as catalysts for functionalization of the aromatic C−H bond. The tripodalligand-based complexes exhibited distorted trigonal-bipyramidal (TBP) geometry (τ, 0.70) around the copper(II) center; however, diazepaneligand-based complexes adopted square-pyramidal (SP) geometry (τ, 0.037). The Cu−N Py bonds (2.003−2.096 Å) are almost identical and shorter than Cu−N amine bonds (2.01−2.148 Å). Also, their Cu−O (Cu− O water , 1.988 Å; Cu−O triflate , 2.33 Å) bond distances are slightly varied. All of the complexes exhibited Cu 2+ → Cu + redox couples in acetonitrile, where the redox potentials of TBP-based complexes (−0.251 to −0.383 V) are higher than those of SP-based complexes (−0.450 to −0.527 V). The d−d bands around 582−757 nm and axial patterns of electron paramagnetic resonance spectra [g ∥ , 2.200−2.251; A ∥ , (146−166) × 10 −4 cm −1 ] of the complexes suggest the existence of five-coordination geometry. The bonding parameters showed K ∥ > K ⊥ for all complexes, corresponding to out-ofplane π bonding. The complexes catalyzed direct hydroxylation of benzene using 30% H 2 O 2 and afforded phenol exclusively. The complexes with TBP geometry exhibited the highest amount of phenol formation (37%) with selectivity (98%) superior to that of diazepane-based complexes (29%), which preferred to adopt SP-based geometry. Hydroxylation of benzene likely proceeded via a Cu II -OOH key intermediate, and its formation has been established by electrospray ionization mass spectrometry, vibrational, and electronic spectra. Their formation constants have been calculated as (2.54−11.85) × 10 −2 s −1 from the appearance of an O (π* σ ) → Cu ligand-to-metal charge-transfer transition around 370−390 nm. The kinetic isotope effect (KIE) experiments showed values of 0.97−1.12 for all complexes, which further supports the crucial role of Cu-OOH in catalysis. The 18 O-labeling studies using H 2 18 O 2 showed a 92% incorporation of 18 O into phenol, which confirms H 2 O 2 as the key oxygen supplier. Overall, the coordination geometry of the complexes strongly influenced the catalytic efficiencies. The geometry of one of the Cu II -OOH intermediates has been optimized by the density functional theory method, and its calculated electronic and vibrational spectra are almost similar to the experimentally observed values.

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“…As the same ligand behaves as a straightforward mononucleating quadridentate in the copper and nickel complexes (O'Connor et al, 2012;Muthuramalingam et al, 2017Muthuramalingam et al, , 2019a, this led to the question as to whether the coordination is governed by the ligand bite vs the larger ionic radius of Co 2+ vs Cu 2+ /Ni 2+ . This proposal was approached by synthesising the homopiperazine analogue, Phpz, whose ligand has a larger (N2-N2A) bite.…”

Section: Structural Commentarymentioning

confidence: 99%

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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One step phenol synthesis from benzene catalysed by nickel(ii) complexes

Abstract: Nickel(ii)complexes of N4-ligands are reported as efficient catalysts for direct benzene hydroxylation via bis(μ-oxo)dinickel(iii) intermediate species. The exclusive phenol formation is achieved with a yield of 41%.

Cited by 26 publications

References 54 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

Benzene Hydroxylation by Bioinspired Copper(II) Complexes: Coordination Geometry versus Reactivity

Chlorocobalt complexes with pyridylethyl-derived diazacycloalkanes

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