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Inorganics
Special Issues
N-Heterocyclic Carbene Metal Complexes: Synthesis, Properties and Applications
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N-Heterocyclic Carbene Metal Complexes: Synthesis, Properties and Applications

A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Organometallic Chemistry".

Deadline for manuscript submissions: closed (15 June 2023) | Viewed by 8113

Special Issue Editors

Dr. Kostiantyn Marichev

E-Mail Website
Guest Editor
Department of Chemistry, Georgia State University, Atlanta, GA 30303, USA
Interests: organic synthesis; organometallic chemistry; asymmetric reactions; catalysis; heterocyclic chemistry
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Alejandro Bugarin

E-Mail Website
Guest Editor
Department of Chemistry & Physics, Florida Gulf Coast University, Fort Myers, FL 33965, USA
Interests: organic chemistry; photochemistry; natural products
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

N-Heterocyclic carbenes (NHCs) are nitrogen-containing cyclic carbenes stabilized by one or two heteroatoms. Since the isolation and characterization of the first stable crystalline free NHC by Arduengo in 1991, interest to this class of compounds has dramatically increased. As the study of NHCs, their properties, and ability to coordinate with transition metals has continued, reports on applications of NHC–metal complexes have attracted more researchers to the field. NHC–metal complexes can be formed with both soft and hard metal ions, leading to additional applications. NHC ligands have numerous advantages over conventional phosphine or nitrogen ligands, such as outstanding σ donor and poor π acceptor abilities; that way, they form stronger NHC–metal bonds. Many reports indicate that NHC–metal complexes have proven to be more effective in most catalytic reactions than, for example, metal–phosphine complexes. Transition metal–NHC complexes, due to the presence of d-orbitals and ability to change oxidation state, are among the most used in modern catalysis. A number of complexes have exhibited unusual physicochemical properties and found applications in material science and electronics. Furthermore, NHC–metal complexes, particularly of silver(I), gold(I), and palladium(II), have been identified as active antimicrobial and anticancer agents with bioactivities similar to or exceeding those of drugs that are currently on the market. Although a number of stable NHCs and their metallic complexes are now commercially available, there are still open and constantly growing opportunities for this field of study due to their intrinsic structural diversity.

This Special Issue aims to cover recent advances in the field of N-heterocyclic carbene metal complexes. It includes the design and preparation of new NHC ligands and their coordination with transition metals, characterization, physicochemical properties, application in catalytic reactions, material science, medicinal chemistry, polymers, and access to commercially valuable molecules, drugs, and natural products.

Dr. Kostiantyn Marichev
Prof. Dr. Alejandro Bugarin
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Inorganics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • NHC–metal complexes
  • σ-donors
  • ligand design
  • catalysis
  • polymers
  • antimicrobial and anticancer activity
  • magneto- and photochemistry

Related Special Issue

Published Papers (5 papers)

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Research

12 pages, 2631 KiB  
Article
PEPPSI-Type Pd(II)—NHC Complexes on the Base of p-tert-Butylthiacalix[4]arene: Synthesis and Catalytic Activities
by Bulat Gafiatullin, Aigul Akchurina, Angelina Fedoseeva, Elza Sultanova, Daut Islamov, Konstantin Usachev, Vladimir Burilov, Svetlana Solovieva and Igor Antipin
Inorganics 2023, 11(8), 326; https://doi.org/10.3390/inorganics11080326 - 01 Aug 2023
Cited by 2 | Viewed by 1104
Abstract
The creation of effective catalytic systems for cross-coupling reactions, reduction, etc., capable of working in water-organic or pure aqueous media is in great demand. The article presents the synthesis of NHC-palladium complexes of the PEPPSI type based on monoimidazolium derivatives of thiacalix[4]arene. The [...] Read more.
The creation of effective catalytic systems for cross-coupling reactions, reduction, etc., capable of working in water-organic or pure aqueous media is in great demand. The article presents the synthesis of NHC-palladium complexes of the PEPPSI type based on monoimidazolium derivatives of thiacalix[4]arene. The structure of the imidazolium precursors, obtained in 81–88% yields and the complexes themselves, obtained in 40–50% yields, is established using modern methods, including X-ray structural analysis and high-resolution mass spectrometry. It is shown that the obtained complex with bulk substituents near the palladium atom is not inferior to the well-known PEPPSI-type Organ’s catalyst in the catalysis of Suzuki-Miyaura coupling and is four times superior to the latter in the p-nitrophenol reduction reaction. Given the presence of free phenolic hydroxyl groups in the macrocycle, the obtained complexes are of interest for further post-modification or for immobilization on a carrier. Full article
(This article belongs to the Special Issue N-Heterocyclic Carbene Metal Complexes: Synthesis, Properties and Applications)
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11 pages, 2017 KiB  
Article
New Insights into the Catalytic Activity of Second Generation Hoveyda–Grubbs Complexes Having Phenyl Substituents on the Backbone
by Assunta D’Amato, Annaluisa Mariconda and Pasquale Longo
Inorganics 2023, 11(6), 244; https://doi.org/10.3390/inorganics11060244 - 06 Jun 2023
Cited by 1 | Viewed by 1268
Abstract
One of the most effective synthetic pathways to produce unsaturated compounds and polymers, meant for both industrial and pharmaceutical applications, is olefin metathesis. These useful reactions are commonly promoted by ruthenium-based precatalysts, namely the second-generation Grubbs’ catalyst (GII) and complexes bearing a styrenyl [...] Read more.
One of the most effective synthetic pathways to produce unsaturated compounds and polymers, meant for both industrial and pharmaceutical applications, is olefin metathesis. These useful reactions are commonly promoted by ruthenium-based precatalysts, namely the second-generation Grubbs’ catalyst (GII) and complexes bearing a styrenyl ether ligand, referred to as the second-generation Hoveyda–Grubbs’ catalyst (HGII). By altering the steric and electronic characteristics of substituents on the backbone and/or on the nitrogen atoms of the NHC ligand, it is possible to increase the reactivity and stability of second-generation ruthenium catalysts. The synthesis of an HG type II complex bearing two anti-phenyl backbone substituents (anti-HGIIPh-Mes) with mesityl N-substituents is reported. The catalytic performances of the new complex were investigated in standard ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) and compared to those of the analogue complex syn-HGIIPh-Mes and to the classic HGII complex. A thorough analysis of the temperature dependence of the performances, along with a detailed comparison with the commercially available HGII, is conducted. The HGIIPh-Mes complexes are more thermally stable than their parent HGII, as shown by the fact that their activity in the ROMP of 5-ethylidene-2-norbornene does not alter when the polymerization is carried out at room temperature after the complexes have been held at 180 °C for two hours, making them particularly interesting for materials applications. Full article
(This article belongs to the Special Issue N-Heterocyclic Carbene Metal Complexes: Synthesis, Properties and Applications)
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11 pages, 2212 KiB  
Article
Catalysis of a Bis-Caffeine Palladium(II) NHC-Pincer Complex
by Oliver Bysewski, Andreas Winter and Ulrich S. Schubert
Inorganics 2023, 11(4), 164; https://doi.org/10.3390/inorganics11040164 - 13 Apr 2023
Cited by 3 | Viewed by 1573
Abstract
A tridentate bis-NHC Pd complex, based on caffeine, was studied for its catalytic activity. This complex displayed a high catalytic activity in the Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions of aryl halides. The Sonogashira cross-coupling was also investigated but reveals a fast plateauing [...] Read more.
A tridentate bis-NHC Pd complex, based on caffeine, was studied for its catalytic activity. This complex displayed a high catalytic activity in the Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions of aryl halides. The Sonogashira cross-coupling was also investigated but reveals a fast plateauing of the reaction. Aryl iodides as well as aryl bromides react when equipped with either electron-donating or electron-withdrawing substituents. Aryl chlorides, which contained electron-withdrawing groups, were also reactive under the applied conditions. Full article
(This article belongs to the Special Issue N-Heterocyclic Carbene Metal Complexes: Synthesis, Properties and Applications)
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10 pages, 1293 KiB  
Article
Nickel(II) N-Heterocyclic Carbene Complex for the Hydrogenation of 2-Acetylpyridine under Mild Conditions
by Mitu Sharma, Amanda M. Perkins, Alison K. Duckworth, Emily J. Rouse, Bruno Donnadieu, Bhupendra Adhikari, Sean L. Stokes and Joseph P. Emerson
Inorganics 2023, 11(3), 120; https://doi.org/10.3390/inorganics11030120 - 14 Mar 2023
Cited by 3 | Viewed by 1461
Abstract
Catalyst-mediated hydrogenation of ketones via hydride transfer can be directly used in the synthesis of alcohols which can exhibit great potential in the practical synthesis of pharmaceuticals. The application of Ni-NHC complexes in the hydrogenation of ketones is still limited. In a pursuit [...] Read more.
Catalyst-mediated hydrogenation of ketones via hydride transfer can be directly used in the synthesis of alcohols which can exhibit great potential in the practical synthesis of pharmaceuticals. The application of Ni-NHC complexes in the hydrogenation of ketones is still limited. In a pursuit to study the effect of Ni-NHC-based complexes in the reactivity towards hydrogenation, we have studied the catalytic efficiency of a pendent-type nickel complex [Ni(NHC)2](PF6)2 constructed from a benzimidazole moiety. The hydrogenation of 2-acetylpyridine was studied with respect to catalyst loading, reaction temperature, reaction time, and solvent medium. The complex was broadly characterized by X-ray crystallography, ESI-MS, NMR, UV-Vis, and IR spectral studies. Full article
(This article belongs to the Special Issue N-Heterocyclic Carbene Metal Complexes: Synthesis, Properties and Applications)
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17 pages, 2500 KiB  
Article
Combining a Low Valent Molybdenum(0) Center with a Strongly σ-Donating Mesoionic Carbene Chelate Ligand—Synthesis and Structural Characterization
by Benedict Josua Elvers, Paul Schulan, Sebastian Pätsch, Christian Fischer and Carola Schulzke
Inorganics 2022, 10(11), 216; https://doi.org/10.3390/inorganics10110216 - 20 Nov 2022
Viewed by 1658
Abstract
Triazolylidene ligands belong to a class of N-heterocyclic carbenes of growing chemical interest. Their precursors are readily available using Click chemistry and, therefore, highly modular for tuning their electronic characteristics. Due to their notable donor properties, these ligands are particularly suitable for modulating [...] Read more.
Triazolylidene ligands belong to a class of N-heterocyclic carbenes of growing chemical interest. Their precursors are readily available using Click chemistry and, therefore, highly modular for tuning their electronic characteristics. Due to their notable donor properties, these ligands are particularly suitable for modulating the electronic properties of the central ions of their complexes. Here, a bidentate bistriazolylidene which is a particularly strong donor ligand is combined with a low valent molybdenum(0) center and four carbon monoxide molecules as co-ligands. The novel complex exhibits characteristic electrochemical and IR-spectroscopic behavior. An X-ray structural analysis provides metrical details which are not entirely in agreement with spectroscopic data, likely going back to crystal packing effects. In comparison with precursor and ligand SCXRD data, notable geometrical changes induced by the coordination of the ligand to the metal can be observed. The analyses strongly support the bistriazolylidene ligand as being a particularly good donor of electron density towards the central metal. Potentially, these findings may support, in the future, the design of potent catalysts for the reductive activation of small molecules. Full article
(This article belongs to the Special Issue N-Heterocyclic Carbene Metal Complexes: Synthesis, Properties and Applications)
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