Research

Jump to: Review

Open AccessArticle

Electrochemical Epoxidation Catalyzed by Manganese Salen Complex and Carbonate with Boron-Doped Diamond Electrode

by

,

,

,

,

,

and

Molecules 2023, 28(4), 1797; https://doi.org/10.3390/molecules28041797 - 14 Feb 2023

Viewed by 429

Abstract

Epoxides are essential precursors for epoxy resins and other chemical products. In this study, we investigated whether electrochemically oxidizing carbonate ions could produce percarbonate to promote an epoxidation reaction in the presence of appropriate metal catalysts, although Tanaka and co-workers had already completed [...] Read more.

Epoxides are essential precursors for epoxy resins and other chemical products. In this study, we investigated whether electrochemically oxidizing carbonate ions could produce percarbonate to promote an epoxidation reaction in the presence of appropriate metal catalysts, although Tanaka and co-workers had already completed a separate study in which the electrochemical oxidation of chloride ions was used to produce hypochlorite ions for electrochemical epoxidation. We found that epoxides could be obtained from styrene derivatives in the presence of metal complexes, including manganese(III) and oxidovanadium(IV) porphyrin complexes and manganese salen complexes, using a boron-doped diamond as the anode. After considering various complexes as potential catalysts, we found that manganese salen complexes showed better performance in terms of epoxide yield. Furthermore, the substituent effect of the manganese salen complex was also investigated, and it was found that the highest epoxide yields were obtained when Jacobsen’s catalyst was used. Although there is still room for improving the yields, this study has shown that the in situ electrochemical generation of percarbonate ions is a promising method for the electrochemical epoxidation of alkenes. Full article

(This article belongs to the Special Issue Design Strategies for Metal Complexes that Activate Bio-Related Small Molecules)

► Show Figures

Graphical abstract

Open AccessArticle

Catalytic Ammonia Synthesis Mediated by Molybdenum Complexes with PN³P Pincer Ligands: Influence of P/N Substituents and Molecular Mechanism

by

,

,

,

and

Molecules 2022, 27(22), 7843; https://doi.org/10.3390/molecules27227843 - 14 Nov 2022

Viewed by 640

Abstract

Three molybdenum trihalogenido complexes supported by different PN³P pincer ligands were synthesized and investigated regarding their activity towards catalytic N₂-to-NH₃ conversion. The highest yields were obtained with the H-PN³P^tBu ligand. The corresponding Mo(V)-nitrido complex also [...] Read more.

Three molybdenum trihalogenido complexes supported by different PN³P pincer ligands were synthesized and investigated regarding their activity towards catalytic N₂-to-NH₃ conversion. The highest yields were obtained with the H-PN³P^tBu ligand. The corresponding Mo(V)-nitrido complex also shows good catalytic activity. Experiments regarding the formation of the analogous Mo(IV)-nitrido complex lead to the conclusion that the mechanism of catalytic ammonia formation mediated by the title systems does not involve N-N cleavage of a dinuclear Mo-dinitrogen complex, but follows the classic Chatt cycle. Full article

(This article belongs to the Special Issue Design Strategies for Metal Complexes that Activate Bio-Related Small Molecules)

► Show Figures

Figure 1

Open AccessArticle

Direct Hydroxylation of Benzene with Hydrogen Peroxide Using Fe Complexes Encapsulated into Mesoporous Y-Type Zeolite

by

,

,

and

Molecules 2022, 27(20), 6852; https://doi.org/10.3390/molecules27206852 - 13 Oct 2022

Viewed by 496

Abstract

Mesoporous Y-type zeolite (MYZ) was prepared by an acid and base treatment of commercial Y-type zeolite (YZ). The mesopore volume of MYZ was six times higher than that of YZ. [Fe(terpy)₂]²⁺ complexes encapsulated into MYZ and YZ with different Fe [...] Read more.

Mesoporous Y-type zeolite (MYZ) was prepared by an acid and base treatment of commercial Y-type zeolite (YZ). The mesopore volume of MYZ was six times higher than that of YZ. [Fe(terpy)₂]²⁺ complexes encapsulated into MYZ and YZ with different Fe contents (Fe(X)L-MYZ and Fe(X)L-YZ; X is the amount of Fe) were prepared and characterized. The oxidation of benzene with H₂O₂ using Fe(X)L-MYZ and Fe(X)L-YZ catalysts was carried out; phenol was selectively produced with all Fe-containing zeolite catalysts. As a result, the oxidation activity of benzene increased with increasing iron complex content in the Fe(X)L-MYZ and Fe(X)L-YZ catalysts. The oxidation activity of benzene using Fe(X)L-MYZ catalyst was higher than that using Fe(X)L-YZ. Furthermore, adding mesopores increased the catalytic activity of the iron complex as the iron complex content increased. Full article

(This article belongs to the Special Issue Design Strategies for Metal Complexes that Activate Bio-Related Small Molecules)

► Show Figures

Figure 1

Open AccessArticle

The Conversion of Superoxide to Hydroperoxide on Cobalt(III) Depends on the Structural and Electronic Properties of Azole-Based Chelating Ligands

by

,

,

,

,

and

Molecules 2022, 27(19), 6416; https://doi.org/10.3390/molecules27196416 - 28 Sep 2022

Viewed by 573

Abstract

Conversion from superoxide (O₂⁻) to hydroperoxide (OOH⁻) on the metal center of oxygenases and oxidases is recognized to be a key step to generating an active species for substrate oxidation. In this study, reactivity of cobalt(III)-superoxido complexes supported [...] Read more.

Conversion from superoxide (O₂⁻) to hydroperoxide (OOH⁻) on the metal center of oxygenases and oxidases is recognized to be a key step to generating an active species for substrate oxidation. In this study, reactivity of cobalt(III)-superoxido complexes supported by facially-capping tridentate tris(3,5-dimethyl-4-X-pyrazolyl)hydroborate ([HB(pz^Me2,X)₃]⁻; Tp^Me2,X) and bidentate bis(1-methyl-imidazolyl)methylborate ([B(Im^N^-Me)₂Me(Y)]⁻; L^Y) ligands toward H-atom donating reagent (2-hydroxy-2-azaadamantane; AZADOL) has been explored. The oxygenation of the cobalt(II) precursors give the corresponding cobalt(III)-superoxido complexes, and the following reaction with AZADOL yield the hydroperoxido species as has been characterized by spectroscopy (UV-vis, resonance Raman, EPR). The reaction of the cobalt(III)-superoxido species and a reducing reagent ([Co^II(C₅H₅)₂]; cobaltocene) with proton (trifluoroacetic acid; TFA) also yields the corresponding cobalt(III)-hydroperoxido species. Kinetic analyses of the formation rates of the cobalt(III)-hydroperoxido complexes reveal that second-order rate constants depend on the structural and electronic properties of the cobalt-supporting chelating ligands. An electron-withdrawing ligand opposite to the superoxide accelerates the hydrogen atom transfer (HAT) reaction from AZADOL due to an increase in the electrophilicity of the superoxide ligand. Shielding the cobalt center by the alkyl group on the boron center of bis(imidazolyl)borate ligands hinders the approaching of AZADOL to the superoxide, although the steric effect is insignificant. Full article

(This article belongs to the Special Issue Design Strategies for Metal Complexes that Activate Bio-Related Small Molecules)

► Show Figures

Figure 1

Open AccessArticle

The Steric Effect in Preparations of Vanadium(II)/(III) Dinitrogen Complexes of Triamidoamine Ligands Bearing Bulky Substituents

by

,

,

,

,

,

,

and

Molecules 2022, 27(18), 5864; https://doi.org/10.3390/molecules27185864 - 09 Sep 2022

Viewed by 666

Abstract

The reactions of newly designed lithiated triamidoamines Li₃L^R (R = iPr, Pen, and Cy₂) with VCl₃(THF)₃ under N₂ yielded dinitrogen–divanadium complexes with a μ-N₂ between vanadium atoms [{V(L^R)}₂ [...] Read more.

The reactions of newly designed lithiated triamidoamines Li₃L^R (R = iPr, Pen, and Cy₂) with VCl₃(THF)₃ under N₂ yielded dinitrogen–divanadium complexes with a μ-N₂ between vanadium atoms [{V(L^R)}₂(μ-N₂)] (R = iPr (1) and Pen (2)) for the former two, while not dinitrogen–divanadium complexes but a mononuclear vanadium complex with a vacant site, [V(L^Cy2)] (R = Cy₂ (3)), were obtained for the third ligand. The V–N_N2 and N–N distances were 1.7655(18) and 1.219(4) Å for 1 and 1.7935(14) and 1.226(3) Å for 2, respectively. The ν(¹⁴N–¹⁴N) stretching vibrations of 1 and 2, as measured using resonance Raman spectroscopy, were detected at 1436 and 1412 cm^–1, respectively. Complex 3 reacted with potassium metal in the presence of 18-crown-6-ether under N₂ to give a hetero-dinuclear vanadium complex with μ-N₂ between vanadium and potassium, [VK(L^Cy2)(μ-N₂)(18-crown-6)] (4). The N–N distance and ν(¹⁴N–¹⁴N) stretching for 4 were 1.152(3) Å and 1818 cm⁻¹, respectively, suggesting that 4 is more activated than complexes 1 and 2. The complexes 1, 2, 3, and 4 reacted with HOTf and K[C₁₀H₈] to give NH₃ and N₂H₄. The yields of NH₃ and N₂H₄ (per V atom) were 47 and 11% for 1, 38 and 16% for 2, 77 and 7% for 3, and 80 and 5% for 4, respectively, and 3 and 4, which have a ligand L^Cy2, showed higher reactivity than 1 and 2. Full article

(This article belongs to the Special Issue Design Strategies for Metal Complexes that Activate Bio-Related Small Molecules)

► Show Figures

Figure 1

Open AccessArticle

Lewis Acid-Induced Dinitrogen Cleavage in an Anionic Side-on End-on Bound Dinitrogen Diniobium Hydride Complex

by

Naofumi Suzuki

,

Yutaka Ishida

and

Hiroyuki Kawaguchi

Molecules 2022, 27(17), 5553; https://doi.org/10.3390/molecules27175553 - 29 Aug 2022

Viewed by 638

Abstract

The side-on end-on dinitrogen hydride complex [{Na(dme)}₂{(O₃)Nb}₂(μ-η¹:η²-N₂)(μ-H)₂] (3-Na, [O₃]³⁻ = [(3,5-^tBu₂-2-O-C₆H₂)₃CH]³⁻) was [...] Read more.

The side-on end-on dinitrogen hydride complex [{Na(dme)}₂{(O₃)Nb}₂(μ-η¹:η²-N₂)(μ-H)₂] (3-Na, [O₃]³⁻ = [(3,5-^tBu₂-2-O-C₆H₂)₃CH]³⁻) was observed to undergo facile elimination of H₂ and cleavage of the N–N bond in the presence of 9-borabicyclo[3.3.1]nonane (9-BBN), AlMe₃, and ZnMe₂. Treatment of 3-Na with 9-BBN and ZnMe₂ afforded the nitride complex [{K(dme)₂}₂{(O₃)Nb}₂(μ-N)₂] (2-Na). The reaction of 3-Na with AlMe₃ afforded [{Na(dme)}₂{(O₃)AlMe}₂(NbMe₂)₂(μ-N)₂] (5). The nitride complex 2-Na was treated with 9-BBN and AlMe₃ to form [{Na(dme)}₂{(O₃)Nb}(μ-NH)(μ-NBC₈H₁₄){Nb(O₃C)}] (4) and 5, respectively. Complex 2-Na, 4, and 5 were structurally characterized. Full article

(This article belongs to the Special Issue Design Strategies for Metal Complexes that Activate Bio-Related Small Molecules)

► Show Figures

Graphical abstract

Open AccessArticle

Synthesis and Reactivity of Manganese Complexes Bearing Anionic PNP- and PCP-Type Pincer Ligands toward Nitrogen Fixation

by

Shogo Kuriyama

,

Shenglan Wei

,

Takeru Kato

and

Yoshiaki Nishibayashi

Molecules 2022, 27(7), 2373; https://doi.org/10.3390/molecules27072373 - 06 Apr 2022

Cited by 2 | Viewed by 1540

Abstract

A series of manganese complexes bearing an anionic pyrrole-based PNP-type pincer ligand and an anionic benzene-based PCP-type pincer ligand is synthesized and characterized. The reactivity of these complexes toward ammonia formation and silylamine formation from dinitrogen under mild conditions is evaluated to produce [...] Read more.

A series of manganese complexes bearing an anionic pyrrole-based PNP-type pincer ligand and an anionic benzene-based PCP-type pincer ligand is synthesized and characterized. The reactivity of these complexes toward ammonia formation and silylamine formation from dinitrogen under mild conditions is evaluated to produce only stoichiometric amounts of ammonia and silylamine, probably because the manganese pincer complexes are unstable under reducing conditions. Full article

(This article belongs to the Special Issue Design Strategies for Metal Complexes that Activate Bio-Related Small Molecules)

► Show Figures

Figure 1

Review

Jump to: Research

Open AccessReview

π–π Stacking Interaction of Metal Phenoxyl Radical Complexes

by

Hiromi Oshita

and

Yuichi Shimazaki

Molecules 2022, 27(3), 1135; https://doi.org/10.3390/molecules27031135 - 08 Feb 2022

Viewed by 1197

Abstract

π–π stacking interaction is well-known to be one of the weak interactions. Its importance in the stabilization of protein structures and functionalization has been reported for various systems. We have focused on a single copper oxidase, galactose oxidase, which has the π–π stacking [...] Read more.

π–π stacking interaction is well-known to be one of the weak interactions. Its importance in the stabilization of protein structures and functionalization has been reported for various systems. We have focused on a single copper oxidase, galactose oxidase, which has the π–π stacking interaction of the alkylthio-substituted phenoxyl radical with the indole ring of the proximal tryptophan residue and catalyzes primary alcohol oxidation to give the corresponding aldehyde. This stacking interaction has been considered to stabilize the alkylthio-phenoxyl radical, but further details of the interaction are still unclear. In this review, we discuss the effect of the π–π stacking interaction of the alkylthio-substituted phenoxyl radical with an indole ring. Full article

(This article belongs to the Special Issue Design Strategies for Metal Complexes that Activate Bio-Related Small Molecules)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Special Issue "Design Strategies for Metal Complexes that Activate Bio-Related Small Molecules"

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (8 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI