Cu(<scp>i</scp>) complexes obtained<i>via</i>spontaneous reduction of Cu(<scp>ii</scp>) complexes supported by designed bidentate ligands: bioinspired Cu(<scp>i</scp>) based catalysts for aromatic hydroxylation

Kumari, Sheela; Muthuramalingam, Sethuraman; Dhara, Ashish Kumar; Mayilmurugan, Ramasamy; Ghosh, Kaushik

doi:10.1039/d0dt02413a

Cited by 22 publications

(24 citation statements)

References 65 publications

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“…We suspect in situ reduction of Cu(II) to Cu(I) upon coordination to L with simultaneous oxidation of the ligand (additional diamagnetic signals in the 1 H and 31 P{ 1 H} spectra), as was already reported in the literature. 44 − 47 We thus aimed for the Cu(I) complex Cu Cl , which could be successfully synthesized starting directly from CuCl. The identical NMR spectra and crystal structures (data not shown) of the products synthesized from CuCl 2 and CuCl supported this approach.…”

Section: Resultsmentioning

confidence: 99%

Systematic Variation of 3d Metal Centers in a Redox-Innocent Ligand Environment: Structures, Electrochemical Properties, and Carbon Dioxide Activation

et al. 2021

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Coordination compounds of earth-abundant 3d transition metals are among the most effective catalysts for the electrochemical reduction of carbon dioxide (CO 2 ). While the properties of the metal center are crucial for the ability of the complexes to electrochemically activate CO 2 , systematic variations of the metal within an identical, redox-innocent ligand backbone remain insufficiently investigated. Here, we report on the synthesis, structural and spectroscopic characterization, and electrochemical investigation of a series of 3d transition-metal complexes [M = Mn(I), Fe(II), Co(II), Ni(II), Cu(I), and Zn(II)] coordinated by a new redox-innocent PNP pincer ligand system. Only the Fe, Co, and Ni complexes reveal distinct metal-centered electrochemical reductions from M(II) down to M(0) and show indications for interaction with CO 2 in their reduced states. The Ni(0) d 10 species associates with CO 2 to form a putative Aresta-type Ni-η 2 -CO 2 complex, where electron transfer to CO 2 through back-bonding is insufficient to enable electrocatalytic activity. By contrast, the Co(0) d 9 intermediate binding CO 2 can undergo additional electron uptake into a formal cobalt(I) metallacarboxylate complex able to promote turnover. Our data, together with the few literature precedents, single out that an unsaturated coordination sphere (coordination number = 4 or 5) and a d 7 -to-d 9 configuration in the reduced low oxidation state (+I or 0) are characteristics that foster electrochemical CO 2 activation for complexes based on redox-innocent ligands.

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Section: Resultsmentioning

confidence: 99%

Systematic Variation of 3d Metal Centers in a Redox-Innocent Ligand Environment: Structures, Electrochemical Properties, and Carbon Dioxide Activation

et al. 2021

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“…Very recently, a series of Cu(I) complexes ( 65a – 65g ) (Figure ) obtained from the spontaneous reduction of corresponding Cu(II) complexes have been reported for benzene hydroxylation using H 2 O 2 as the oxidant . A correlation between electrochemical behavior and catalytic activity was obvious as the complexes having more negative reduction potential exhibited superior catalytic performances.…”

Section: Copper Complexesmentioning

confidence: 99%

“…A correlation between electrochemical behavior and catalytic activity was obvious as the complexes having more negative reduction potential exhibited superior catalytic performances. Complex 65g bearing electron-releasing groups such as −OH and −OCH 3 was found to be the most promising catalyst among the series with a phenol yield of 29.3%, a TON of 586, and a selectivity of 98.3% …”

Section: Copper Complexesmentioning

confidence: 99%

“…However, the formation of halobenzenes in the presence of CCl 4 and CBrCl 3 suggested the generation of a phenyl radical at some point of the catalysis, and this accounts for the rebound mechanism. A negative ρ value of −0.75 obtained for complex 64h from the Hammett plot of monosubstituted benzenes substantiated the possibility of an electrophilic aromatic substitution mechanism. , Mechanistic investigation of benzene oxidation catalyzed by complex 65g (Figure ) was done using electronic absorption spectroscopy, and the formation of a Cu(II) species during the H 2 O 2 activation was identified . The decay of the MLCT band at 398 nm and simultaneous formation of a 600 nm d–d band suggested the formation of Cu(II) species during the oxidation.…”

Section: Copper Complexesmentioning

confidence: 99%

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Rational Design of First-Row Transition Metal Complexes as the Catalysts for Oxidation of Arenes: A Homogeneous Approach

2022

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Researchers have always been intrigued by one-step selective hydroxylation of aromatic compounds since achieving adequate selectivity toward the target product and avoiding overoxidation are challenging. However, the naturally available oxygenase enzymes efficiently and selectively perform such transformations under normal atmospheric conditions. Inspired by naturally occurring oxygenase enzymes, researchers have undertaken numerous attempts to catalyze the oxidation of arenes using homogeneous and heterogeneous catalysts. In this regard, the first-row transition metal complexes are considered as candidates due to their abundance and redox characteristics. Therefore, this review focuses on catalyst design strategies to improve the efficiency and selectivity of arene oxidation and illustrates the distinctive homogeneous approaches reported in this area by employing first-row transition metal complexes.

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“…Numerous homogeneous catalysts have been tested [25][26][27], such as high active Co complexes [28], Ni complexes [29], Cu-based complexes [30][31][32][33][34], as well as nitrogen- [35,36] or oxygen-ligated [37,38] iron complexes. Additionally, Os complexes were discussed as non-trivial catalysts for benzene oxidation (oxidation with H 2 16 O 2 under 18 O 2 gave phenol that did not contain the 18 O isotope), pointing out "Os=O" as oxidizing species responsible for phenol formation [39].…”

Section: Homogeneous and Heterogeneous Catalysts For The One-step Cat...mentioning

confidence: 99%

One-Step Catalytic or Photocatalytic Oxidation of Benzene to Phenol: Possible Alternative Routes for Phenol Synthesis?

et al. 2020

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Phenol is an important chemical compound since it is a precursor of the industrial production of many materials and useful compounds. Nowadays, phenol is industrially produced from benzene by the multi-step “cumene process”, which is energy consuming due to high temperature and high pressure. Moreover, in the “cumene process”, the highly explosive cumene hydroperoxide is produced as an intermediate. To overcome these disadvantages, it would be useful to develop green alternatives for the synthesis of phenol that are more efficient and environmentally benign. In this regard, great interest is devoted to processes in which the one-step oxidation of benzene to phenol is achieved, thanks to the use of suitable catalysts and oxidant species. This review article discusses the direct oxidation of benzene to phenol in the liquid phase using different catalyst formulations, including homogeneous and heterogeneous catalysts and photocatalysts, and focuses on the reaction mechanisms involved in the selective conversion of benzene to phenol in the liquid phase.

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Cu(i) complexes obtainedviaspontaneous reduction of Cu(ii) complexes supported by designed bidentate ligands: bioinspired Cu(i) based catalysts for aromatic hydroxylation

Abstract: Copper(I) complexes [Cu(L1-7)2](ClO4) (1-7) of bidentate ligands (L1-L7) have been synthesized via spontaneous reduction and characterized as the catalysts for aromatic C-H activation using H2O2 as oxidant. The single crystal...

Cited by 22 publications

References 65 publications

Systematic Variation of 3d Metal Centers in a Redox-Innocent Ligand Environment: Structures, Electrochemical Properties, and Carbon Dioxide Activation

Systematic Variation of 3d Metal Centers in a Redox-Innocent Ligand Environment: Structures, Electrochemical Properties, and Carbon Dioxide Activation

Rational Design of First-Row Transition Metal Complexes as the Catalysts for Oxidation of Arenes: A Homogeneous Approach

One-Step Catalytic or Photocatalytic Oxidation of Benzene to Phenol: Possible Alternative Routes for Phenol Synthesis?

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