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Sustainable Metals: Ligand Design, Complexes, and Catalytic Applications
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Sustainable Metals: Ligand Design, Complexes, and Catalytic Applications

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (31 January 2021) | Viewed by 15801

Special Issue Editors

Prof. Dr. Andreas A. Danopoulos

E-Mail Website
Guest Editor
Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 15771 Athens, Greece
Interests: inorganic chemistry; organometallic chemistry; homogeneous catalysis; ligand design
Prof. Dr. Georgios C. Vougioukalakis

E-Mail Website
Guest Editor
Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, 15771 Athens, Greece
Interests: organic chemistry; catalysis; organometallic chemistry; materials chemistry; nanostructures; physical organic chemistry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The sustainable development of societies is one of the world’s current “grand challenges”. During the last two decades, chemistry has been heavily pushing in this direction, aimed at reducing the utilization of the Earth’s less-abundant resources and the generation of hazardous substances and by-products. Metal-catalysed transformations are at the crossroad of the efforts to develop innovative, transformative, and economically-viable ways to reduce the environmental impact of chemical industries. One of the most demanding objectives in this regard is the elimination of less-abundant and/or non-biologically-relevant metals in catalytic toolboxes relevant to the preparation of commodity and fine chemicals, pharmaceuticals, organic synthons, polymers, etc. The utilization of sustainable energy forms (light and electricity) for catalytic chemical reactions should also be based on the wise use of cheap and abundant base metals.

Some emerging strategies for catalytic innovations with base metals either involve “mimicking” precious metal reactivity, by combining ligand and metal redox changes within catalytic cycles, or guiding base metals to unravel their own specific catalytic potential, for example by addressing adverse stability issues (thermal and air) under catalytic conditions, managing electron- and ligand-deficient metal structures, driving pathways through densely populated spin states, and successfully manipulating single electron redox changes and paramagnetic intermediates. A major potential to tune these peculiarities and promote sustainable base metal catalysis lies in the successful and precise design of novel ligands and the creative use of already established lignands.

The goal of the present Special Issue of Molecules is to provide a forum for the discussion of the recent developments in all fields of sustainable metals chemistry and catalysis. We invite original research articles, reviews, and commentaries in the fields of innovative ligand design, metal complex development, catalytic applications, and related mechanistic studies and theoretical calculations.

Prof. Dr. Andreas A. Danopoulos
Prof. Dr. Georgios C. Vougioukalakis
Guest Editors

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Keywords

  • Sustainable catalysis
  • Green chemistry
  • Sustainable metals
  • Ligand design
  • Coordination chemistry
  • Organometallic chemistry
  • N-heterocyclic carbenes
  • Non-innocent ligands
  • Bifunctional catalysis
  • Electrocatalysis
  • Photocatalysis

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Published Papers (4 papers)

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Research

20 pages, 4407 KiB  
Article
Towards Iron(II) Complexes with Octahedral Geometry: Synthesis, Structure and Photophysical Properties
by Mohamed Darari, Antonio Francés-Monerris, Bogdan Marekha, Abdelatif Doudouh, Emmanuel Wenger, Antonio Monari, Stefan Haacke and Philippe C. Gros
Molecules 2020, 25(24), 5991; https://doi.org/10.3390/molecules25245991 - 17 Dec 2020
Cited by 23 | Viewed by 5542
Abstract
The control of ligand-field splitting in iron (II) complexes is critical to slow down the metal-to-ligand charge transfer (MLCT)-excited states deactivation pathways. The gap between the metal-centered states is maximal when the coordination sphere of the complex approaches an ideal octahedral geometry. Two [...] Read more.
The control of ligand-field splitting in iron (II) complexes is critical to slow down the metal-to-ligand charge transfer (MLCT)-excited states deactivation pathways. The gap between the metal-centered states is maximal when the coordination sphere of the complex approaches an ideal octahedral geometry. Two new iron(II) complexes (C1 and C2), prepared from pyridylNHC and pyridylquinoline type ligands, respectively, have a near-perfect octahedral coordination of the metal. The photophysics of the complexes have been further investigated by means of ultrafast spectroscopy and TD-DFT modeling. For C1, it is shown that—despite the geometrical improvement—the excited state deactivation is faster than for the parent pseudo-octahedral C0 complex. This unexpected result is due to the increased ligand flexibility in C1 that lowers the energetic barrier for the relaxation of 3MLCT into the 3MC state. For C2, the effect of the increased ligand field is not strong enough to close the prominent deactivation channel into the metal-centered quintet state, as for other Fe-polypyridine complexes. Full article
(This article belongs to the Special Issue Sustainable Metals: Ligand Design, Complexes, and Catalytic Applications)
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13 pages, 5173 KiB  
Article
DFT Study on the Mechanism of Iron-Catalyzed Diazocarbonylation
by Tímea R. Kégl, László Kollár and Tamás Kégl
Molecules 2020, 25(24), 5860; https://doi.org/10.3390/molecules25245860 - 11 Dec 2020
Cited by 1 | Viewed by 2497
Abstract
The mechanism of the carbonylation of diazomethane in the presence of iron–carbonyl–phosphine catalysts has been investigated by means of DFT calculations at the M06/def-TZVP//B97D3/def2-TZVP level of theory, in combination with the SMD solvation method. The reaction rate is determined by the formation of [...] Read more.
The mechanism of the carbonylation of diazomethane in the presence of iron–carbonyl–phosphine catalysts has been investigated by means of DFT calculations at the M06/def-TZVP//B97D3/def2-TZVP level of theory, in combination with the SMD solvation method. The reaction rate is determined by the formation of the coordinatively unsaturated doublet-state Fe(CO)3(P) precursor followed by the diazoalkane coordination and the N2 extrusion. The free energy of activation is predicted to be 18.5 and 28.2 kcal/mol for the PF3 and PPh3 containing systems, respectively. Thus, in the presence of less basic P-donor ligands with stronger π-acceptor properties, a significant increase in the reaction rate can be expected. According to energy decomposition analysis combined with natural orbitals of chemical valence (EDA–NOCV) calculations, diazomethane in the Fe(CO)3(phosphine)(η1-CH2N2) adduct reveals a π-donor–π-acceptor type of coordination. Full article
(This article belongs to the Special Issue Sustainable Metals: Ligand Design, Complexes, and Catalytic Applications)
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11 pages, 1792 KiB  
Article
Bis-Phenoxo-CuII2 Complexes: Formal Aromatic Hydroxylation via Aryl-CuIII Intermediate Species
by Xavi Ribas, Raül Xifra and Xavier Fontrodona
Molecules 2020, 25(20), 4595; https://doi.org/10.3390/molecules25204595 - 9 Oct 2020
Cited by 1 | Viewed by 2311
Abstract
Ullmann-type copper-mediated arylC-O bond formation has attracted the attention of the catalysis and organometallic communities, although the mechanism of these copper-catalyzed coupling reactions remains a subject of debate. We have designed well-defined triazamacrocyclic-based aryl-CuIII complexes as an ideal platform to study the [...] Read more.
Ullmann-type copper-mediated arylC-O bond formation has attracted the attention of the catalysis and organometallic communities, although the mechanism of these copper-catalyzed coupling reactions remains a subject of debate. We have designed well-defined triazamacrocyclic-based aryl-CuIII complexes as an ideal platform to study the C-heteroatom reductive elimination step with all kinds of nucleophiles, and in this work we focus our efforts on the straightforward synthesis of phenols by using H2O as nucleophile. Seven well-defined aryl-CuIII complexes featuring different ring size and different electronic properties have been reacted with water in basic conditions to produce final bis-phenoxo-CuII2 complexes, all of which are characterized by XRD. Mechanistic investigations indicate that the reaction takes place by an initial deprotonation of the NH group coordinated to CuIII center, subsequent reductive elimination with H2O as nucleophile to form phenoxo products, and finally air oxidation of the CuI produced to form the final bis-phenoxo-CuII2 complexes, whose enhanced stability acts as a thermodynamic sink and pushes the reaction forward. Furthermore, the corresponding triazamacrocyclic-CuI complexes react with O2 to undergo 1e− oxidation to CuII and subsequent C-H activation to form aryl-CuIII species, which follow the same fate towards bis-phenoxo-CuII2 complexes. This work further highlights the ability of the triazamacrocyclic-CuIII platform to undergo aryl-OH formation by reductive elimination with basic water, and also shows the facile formation of rare bis-phenoxo-CuII2 complexes. Full article
(This article belongs to the Special Issue Sustainable Metals: Ligand Design, Complexes, and Catalytic Applications)
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18 pages, 2519 KiB  
Article
Synthesis, Characterization, Catalytic Activity, and DFT Calculations of Zn(II) Hydrazone Complexes
by Temiloluwa T. Adejumo, Nikolaos V. Tzouras, Leandros P. Zorba, Dušanka Radanović, Andrej Pevec, Sonja Grubišić, Dragana Mitić, Katarina K. Anđelković, Georgios C. Vougioukalakis, Božidar Čobeljić and Iztok Turel
Molecules 2020, 25(18), 4043; https://doi.org/10.3390/molecules25184043 - 4 Sep 2020
Cited by 57 | Viewed by 4848
Abstract
Two new Zn(II) complexes with tridentate hydrazone-based ligands (condensation products of 2-acetylthiazole) were synthesized and characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction methods. The complexes 1, 2 and recently synthesized [ZnL3(NCS) [...] Read more.
Two new Zn(II) complexes with tridentate hydrazone-based ligands (condensation products of 2-acetylthiazole) were synthesized and characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction methods. The complexes 1, 2 and recently synthesized [ZnL3(NCS)2] (L3 = (E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)ethan-1-aminium) complex 3 were tested as potential catalysts for the ketone-amine-alkyne (KA2) coupling reaction. The gas-phase geometry optimization of newly synthesized and characterized Zn(II) complexes has been computed at the density functional theory (DFT)/B3LYP/6–31G level of theory, while the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO and LUMO) energies were calculated within the time-dependent density functional theory (TD-DFT) at B3LYP/6-31G and B3LYP/6-311G(d,p) levels of theory. From the energies of frontier molecular orbitals (HOMO–LUMO), the reactivity descriptors, such as chemical potential (μ), hardness (η), softness (S), electronegativity (χ) and electrophilicity index (ω) have been calculated. The energetic behavior of the investigated compounds (1 and 2) has been examined in gas phase and solvent media using the polarizable continuum model. For comparison reasons, the same calculations have been performed for recently synthesized [ZnL3(NCS)2] complex 3. DFT results show that compound 1 has the smaller frontier orbital gap so, it is more polarizable and is associated with a higher chemical reactivity, low kinetic stability and is termed as soft molecule. Full article
(This article belongs to the Special Issue Sustainable Metals: Ligand Design, Complexes, and Catalytic Applications)
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