The Catalytic Efficacy of Co(salen)(AL) in O2 Oxidation Reactions in CO2-Expanded Solvent Media: Axial Ligand Dependence and Substrate Selectivity

Rajagopalan, Bhuma; Cai, Hu; Busch, Daryle H.; Subramaniam, Bala

doi:10.1007/s10562-007-9379-z

Cited by 11 publications

(5 citation statements)

References 37 publications

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“…3 The axial ligand is required for effective catalyst reactivity, as Co(salen) itself binds O 2 poorly. 4 Subsequently, the superoxo adduct abstracts a phenolic hydrogen from the substrate (Fig. 1, reaction III) resulting in a phenoxy radical, which combines with a second equivalent of the superoxo adduct (Fig.…”

Section: Introductionmentioning

confidence: 99%

The effect of axial ligand on the oxidation of syringyl alcohol by Co(salen) adducts

Elder

Bozell

Cedeno

2013

Phys. Chem. Chem. Phys.

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Experimental work on the oxidation of the lignin model, syringyl alcohol, using oxygen and a Co(salen) catalyst has revealed variations in yield with different imidazole-based axial ligands. A reasonable linear relationship was found between product yield and pKa of the axial ligand. The current work, using density functional calculations, examined geometric, electronic, and energetic parameters to determine if additional quantitative relationships can be identified and used in subsequent catalyst design. Good relationships with yield were identified with the geometry of the salen ligand and the charge on the ligand nitrogen coordinated to the cobalt.

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Section: Introductionmentioning

confidence: 99%

The effect of axial ligand on the oxidation of syringyl alcohol by Co(salen) adducts

Elder

Bozell

Cedeno

2013

Phys. Chem. Chem. Phys.

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“… The Co III –superoxo adduct then removes a phenolic hydrogen from the substrate to form a phenoxy radical, which reacts with a second equivalent of the Co III –superoxo adduct to form a peroxo intermediate that undergoes subsequent rearrangement to form quinones, aldehydes, or both. The presence of an axial ligand, such as pyridine, has been shown to facilitate Co III –superoxide formation . Notably, both Co III –hydroxo and Co III –hydroperoxo intermediates are formed during these reactions.…”

Section: Introductionmentioning

confidence: 99%

“…The presence of an axial ligand, such as pyridine, has been shown to facilitate Co III − superoxide formation. 36 Notably, both Co III −hydroxo and Co III −hydroperoxo intermediates are formed during these reactions.…”

Section: ■ Introductionmentioning

confidence: 99%

Co(salen)-Catalyzed Oxidation of Lignin Models to Form Benzoquinones and Benzaldehydes: A Computational and Experimental Study

Cooper

Alam

Nziko

et al. 2020

ACS Sustainable Chem. Eng.

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Lignin is a highly abundant polyphenolic polymer that imparts mechanical strength to plant biomass. Transition-metal complexes can catalyze lignin oxidation to produce value-added products, but low catalytic efficiency has hampered their use in industry. Identifying the chemical and structural factors that govern catalytic activity is a prerequisite to rational design of catalysts with improved activity. Here, we combine computational and experimental approaches to investigate the mechanism of Co(salen)catalyzed oxidation of the monomeric lignin models syringyl (S), vanillyl (G), and 4-hydroxybenzyl alcohol (H) to produce benzoquinone and benzaldehyde products. Experimentally, S oxidation to form dimethoxybenzoquinone proceeded efficiently with a Co(salen) catalyst coordinated by a pyridine ligand, but G and H did not undergo oxidation. Density functional theory calculations reveal that catalyst regeneration is energetically unfavorable in the presence of H, which prevents oxidation. In contrast, S readily facilitates catalyst regeneration. Formation of methoxybenzoquinone from G was achieved experimentally by adding bulky, noncoordinating bases. These findings provide a fundamental baseline for enhancing the activity of Co-Schiff base catalysts toward lignin-like molecules by adding sterically hindered nitrogenous bases or potentially by including a cocatalyst that promotes catalyst regeneration.

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“…Co(salen)/ O 2 oxidation of phenolic and non-phenolic b-O-4 aryl ether lignin model compounds showed very high conversion values within 30 min. [13][14][15] A series of biomimetic oxidation of lignin and lignin model compound using Co(salen) have been successfully studied in our laboratory. [16][17][18][19] Ambrose et al reported the ionic liquid tagged Co(salen) with which veratryl alcohol, a lignin model compound, was selectively oxidized to veratraldehyde using air or pure oxygen as the source of oxygen.…”

Section: Introductionmentioning

confidence: 99%

Application of zeolite-encapsulated Cu(ii) [H4]salen derived from [H2]salen in oxidative delignification of pulp

Zhou

2014

RSC Adv.

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The Catalytic Efficacy of Co(salen)(AL) in O2 Oxidation Reactions in CO2-Expanded Solvent Media: Axial Ligand Dependence and Substrate Selectivity

Cited by 11 publications

References 37 publications

The effect of axial ligand on the oxidation of syringyl alcohol by Co(salen) adducts

The effect of axial ligand on the oxidation of syringyl alcohol by Co(salen) adducts

Co(salen)-Catalyzed Oxidation of Lignin Models to Form Benzoquinones and Benzaldehydes: A Computational and Experimental Study

Application of zeolite-encapsulated Cu(ii) [H4]salen derived from [H2]salen in oxidative delignification of pulp

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