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Special Issue "Carbon Ligands: From Fundamental Aspects to Applications"

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

Deadline for manuscript submissions: 31 July 2020.

Special Issue Editor

Dr. Yves Canac
Website
Guest Editor
Laboratoire de Chimie de Coordination du CNRS (LCC), UPR–8241, 205, route de Narbonne, 31077 Toulouse Cedex 04, France
Interests: My research activities focus on main group chemistry, coordination chemistry, and homogeneous catalysis. Special attention is given on the design, the coordination, and the catalytic properties of electron-rich neutral carbon ligands (carbenes, phosphonium ylides) and electron-poor cationic phosphorus ligands (cyclopropenio- and imidazoliophosphines)

Special Issue Information

Dear Colleagues,

Homogeneous catalysis owes its tremendous development to the advent of a wide range of ligands with well-defined electronic and steric properties, which can finely control the reactivity of organometallic complexes. The ligands involved in catalysis have been centered for a long time on elements of group 15, and it is only more recently that carbon representatives have proved to be valuable alternatives with the emergence of the famous cyclic diaminocarbenes (NHCs). Beyond their activity, the predominance of N- and P-based ligands can be explained by their high stability as opposed to the carbon ligands that have long been thought to be unstable. The isolation of the first stable carbenes proved to be a trigger in the minds of chemists, leading in a short time to remarkable advances in the field of homogeneous catalysis. From there, considerable efforts have been undertaken and carbene ligands have become unavoidable surpassing even their illustrious predecessors in some transformations. Like carbenic species (NHCs, aNHCs (MICS), CAACs, BACs, non-NHCs, etc.), onium (P+, N+, S+) ylides and related (bis-ylides, carbones, carbodiphosphoranes, carbodicarbenes, NHOs, etc.) which are charge-neutral in their free state and act as strong σ-donor ligands, have experienced a revival of interest, thus, confirming their potential as Lewis bases in main group chemistry, coordination chemistry, and in homogeneous catalysis.

The aim of this Special Issue is to provide a contemporary overview of the advances in carbon ligand chemistry. From fundamental aspects to applications, all contributions involving carbon ligands, where the coordinating carbon atom is either of C-sp2 type as in carbenic derivatives, or of C-sp3 type as in ylidic species, are thus welcome.

Dr. Yves Canac
Guest Editor

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 papers will be 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. Molecules is an international peer-reviewed open access semimonthly 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 2000 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

  • Carbon ligand
  • Carbene
  • Ylide
  • Carbon–metal bond
  • Coordination mode
  • Organometallic complex
  • Main group chemistry
  • Coordination chemistry
  • Homogeneous catalysis

Published Papers (5 papers)

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Research

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Open AccessArticle
The Influence of Various N-Heterocyclic Carbene Ligands on Activity of Nitro-Activated Olefin Metathesis Catalysts
Molecules 2020, 25(10), 2282; https://doi.org/10.3390/molecules25102282 - 12 May 2020
Abstract
A set of nitro-activated ruthenium-based Hoveyda-Grubbs type olefin metathesis catalysts bearing sterically modified N-hetero-cyclic carbene (NHC) ligands have been obtained, characterised and studied in a set of model metathesis reactions. It was found that catalysts bearing standard SIMes and SIPr ligands ( [...] Read more.
A set of nitro-activated ruthenium-based Hoveyda-Grubbs type olefin metathesis catalysts bearing sterically modified N-hetero-cyclic carbene (NHC) ligands have been obtained, characterised and studied in a set of model metathesis reactions. It was found that catalysts bearing standard SIMes and SIPr ligands (4a and 4b) gave the best results in metathesis of substrates with more accessible C–C double bonds. At the same time, catalysts bearing engineered naphthyl-substituted NHC ligands (4de) exhibited high activity towards formation of tetrasubstituted C–C double bonds, the reaction which was traditionally Achilles’ heel of the nitro-activated Hoveyda–Grubbs catalyst. Full article
(This article belongs to the Special Issue Carbon Ligands: From Fundamental Aspects to Applications)
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Open AccessFeature PaperArticle
A Self-Assembling NHC-Pd-Loaded Calixarene as a Potent Catalyst for the Suzuki-Miyaura Cross-Coupling Reaction in Water
Molecules 2020, 25(6), 1459; https://doi.org/10.3390/molecules25061459 - 24 Mar 2020
Abstract
Nanoformulated calix[8]arenes functionalized with N-heterocyclic carbene (NHC)-palladium complexes were found to be efficient nano-reactors for Suzuki-Miyaura cross-coupling reactions of water soluble iodo- and bromoaryl compounds with cyclic triol arylborates at low temperature in water without any organic co-solvent. Combined with an improved [...] Read more.
Nanoformulated calix[8]arenes functionalized with N-heterocyclic carbene (NHC)-palladium complexes were found to be efficient nano-reactors for Suzuki-Miyaura cross-coupling reactions of water soluble iodo- and bromoaryl compounds with cyclic triol arylborates at low temperature in water without any organic co-solvent. Combined with an improved one-step synthesis of triol arylborates from boronic acid, this remarkably efficient new tool provided a variety of 4′-arylated phenylalanines and tyrosines in good yields at low catalyst loading with a wide functional group tolerance. Full article
(This article belongs to the Special Issue Carbon Ligands: From Fundamental Aspects to Applications)
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Open AccessArticle
Towards the Preparation of Stable Cyclic Amino(ylide)Carbenes
Molecules 2020, 25(4), 796; https://doi.org/10.3390/molecules25040796 - 12 Feb 2020
Abstract
Cyclic amino(ylide)carbenes (CAYCs) are the ylide-substituted analogues of N-heterocyclic Carbenes (NHCs). Due to the stronger π donation of the ylide compared to an amino moiety they are stronger donors and thus are desirable ligands for catalysis. However, no stable CAYC has been [...] Read more.
Cyclic amino(ylide)carbenes (CAYCs) are the ylide-substituted analogues of N-heterocyclic Carbenes (NHCs). Due to the stronger π donation of the ylide compared to an amino moiety they are stronger donors and thus are desirable ligands for catalysis. However, no stable CAYC has been reported until today. Here, we describe experimental and computational studies on the synthesis and stability of CAYCs based on pyrroles with trialkyl onium groups. Attempts to isolate two CAYCs with trialkyl phosphonium and sulfonium ylides resulted in the deprotonation of the alkyl groups instead of the formation of the desired CAYCs. In case of the PCy3-substituted system, the corresponding ylide was isolated, while deprotonation of the SMe2-functionalized compound led to the formation of ethene and the thioether. Detailed computational studies on various trialkyl onium groups showed that both the α- and β-deprotonated compounds were energetically favored over the free carbene. The most stable candidates were revealed to be α-hydrogen-free adamantyl-substituted onium groups, for which β-deprotonation is less favorable at the bridgehead position. Overall, the calculations showed that the isolation of CAYCs should be possible, but careful design is required to exclude decomposition pathways such as deprotonations at the onium group. Full article
(This article belongs to the Special Issue Carbon Ligands: From Fundamental Aspects to Applications)
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Review

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Open AccessReview
Selenonium Ylides: Syntheses, Structural Aspects, and Synthetic Applications
Molecules 2020, 25(10), 2420; https://doi.org/10.3390/molecules25102420 (registering DOI) - 22 May 2020
Abstract
The goals of this mini review constitute (a) a presentation of the synthetic protocols applied to the preparation of achiral and non-racemic selenonium ylides; (b) discussion of their basic structural features, including their optical activity; and (c) a description of their synthetic applications [...] Read more.
The goals of this mini review constitute (a) a presentation of the synthetic protocols applied to the preparation of achiral and non-racemic selenonium ylides; (b) discussion of their basic structural features, including their optical activity; and (c) a description of their synthetic applications in general synthetic methodology and in asymmetric synthesis. Full article
(This article belongs to the Special Issue Carbon Ligands: From Fundamental Aspects to Applications)
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Open AccessFeature PaperReview
NHC Core Pincer Ligands Exhibiting Two Anionic Coordinating Extremities
Molecules 2020, 25(9), 2231; https://doi.org/10.3390/molecules25092231 - 09 May 2020
Abstract
The chemistry of NHC core pincer ligands of LX2 type bearing two pending arms, identical or not, whose coordinating center is anionic in nature, is here reviewed. In this family, the negative charge of the coordinating atoms can be brought either by [...] Read more.
The chemistry of NHC core pincer ligands of LX2 type bearing two pending arms, identical or not, whose coordinating center is anionic in nature, is here reviewed. In this family, the negative charge of the coordinating atoms can be brought either by a carbon atom via a phosphonium ylide (R3P+–CR2) or by a heteroatom through amide (R2N), oxide (RO), or thio(seleno)oxide (RS, RSe) donor functionalities. Through selected examples, the synthetic methods, coordination properties, and applications of such tridentate systems are described. Particular emphasis is placed on the role of the donor ends in the chemical behavior of these species. Full article
(This article belongs to the Special Issue Carbon Ligands: From Fundamental Aspects to Applications)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Hybrid Gold(I) NHC-Artemether Complexes to Target Falciparum Malaria Parasites

Manel Oujia,b,$, Guillaume Barnouina,$, Álvaro Fernández Álvareza, Jean-Michel Augereaua,b, Catherine Hemmerta,*, Françoise Benoit-Vicala,b,c,* and Heinz Gornitzkaa,*

a CNRS, LCC (Laboratoire de Chimie de Coordination), Université de Toulouse, UPS, INPT, 205 route de Narbonne, BP 44099, F-31077 Toulouse Cedex 4, France

b Institut de Pharmacologie et de Biologie Structurale, IPBS, Université de Toulouse, CNRS, UPS, France

c INSERM, Institut National de la Santé et de la Recherche Médicale, France

$ Participated equally to this work.

Title: Photoluminescent Cu(I) Complexes of Multidentate N,C,N- and P,C,P-Carbodiphosphorane Ligands
Authors: Marius Klein; Nemrud Demirela; Alexander Schinabeckb; Hartmut Yersin; Jörg Sundermeyer
Affiliation: 1. Fachbereich Chemie and Wissenschaftliches Zentrum für Materialwissenschaften, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043 Marburg, Germany 2. Institute for Physical Chemistry, University of Regensburg, 93040 Regensburg, Germany
Abstract: A series of dinuclear copper(I) complexes of multifunctional N,C,N- and P,C,P- carbodiphosphorane (CDP) ligands CDP(Py)2 (1) and (CDP(CH2PPh2)2 (13) have been isolated, spectroscopically and structurally characterized. Their common structural motive is the central double ylidic carbon atom acting as 4-electron donor bridging two copper(I) atoms in close proximity. Neutral complexes were obtained via reaction with CuCl, CuI, and CuSPh precursors, respectively, or via reaction of [(CuCl)2(CDP(Py)2] (2) with sodium carbazolate. Cationic Cu(I) complexes were prepared upon treating 1 with two equivalent of [Cu(NCMe)4]PF6, followed by the addition of either two equivalents of an aryl phosphine (PPh3, P(C6H4OMe)3) or one equivalent of a bridging bisphosphine ligand (DPEPhos, XantPhos, dppf). Carbodiphosphorane (CDP(CH2PPh2)2 (13) was isolated upon treating [CH(dppm)2]Cl (12) with NaNH2 in liquid NH3. However, NMR spectroscopy and DFT calculations reveal, that the double ylidic CDP form of 13 is not the most stable tautomer in gas phase and solution. Nevertheless, the CDP form is trapped from its tautomeric equilibrium, if CuCl, CuI, and CuSPh are reacted with 13 and dinuclear CDP complexes 14-16 are formed. In sharp contrast, 12, the protonated form of neutral zwitterionic ligand 13, acts as cationic pincer ligand towards CuX Lewis acids. Most of the complexes show photoluminescence (PL) upon UV excitation at ambient temperature. For example, for [(CuPPh3)2(CDP(Py)2)](PF6)2 (4) and [(CuSPh)2(CDP(CH2PPh2)2] (16), PL quantum yields (PL) were determined to 36%, and 60%, respectively.

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