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Catalysts
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Tailor-Made NHC Ligands
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Tailor-Made NHC Ligands

A special issue of Catalysts (ISSN 2073-4344).

Deadline for manuscript submissions: closed (15 October 2016) | Viewed by 25513

Special Issue Editor

Dr. Federico Cisnetti

E-Mail Website
Guest Editor
Université Clermont Auvergne, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand (UMR CNRS 6296), BP 10448, F-63000 Clermont-Ferrand, France
Interests: functionalised NHC ligands; preparation of metal-NHC complexes; catalytic biomolecule modification; aqueous-phase catalysis; click chemistry; mechanistic studies

Special Issue Information

Dear Colleagues,

Nowadays, N-heterocyclic carbenes have moved from their initial status of laboratory curiosities to tools widely used in mainstream catalysis, thanks to their remarkable electronic and steric properties. Thanks to the relative ease of synthetic modification, many recent reports deal with the use of tailor-made NHC ligands, i.e., ligands specifically designed to fine-tune a desired property for a given catalytic application. These modifications may consist (non-exhaustive list) in the design of ligands with additional donor groups—multitopic and/or chelating ligands (in some cases displaying hemilability)—adjustment of the steric bulk, of the solubility in media of interest (including novel solvents and water), of the electron donicity. etc. NHC ligands may also be modified to graft catalytically competent complexes onto solid supports.

The aim of this Special Issue is to cover promising recent research and novel trends in catalysis using original NHC ligands (also including other types of stabilized carbenes) specifically designed to solve a problem in catalysis. Contributions from all areas of homogeneous and supported catalysis, based on experimental results and/or molecular modeling, would be of great interest.

Dr. Federico Cisnetti
Guest Editor

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Keywords

  • N-heterocyclic carbenes
  • Ligand design
  • Metal complexes
  • Fine chemicals
  • Homogenous catalysis
  • Supported catalysis

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Published Papers (4 papers)

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Research

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2044 KiB  
Article
Expanding the Scope of Cu(I) Catalyzed “Click Chemistry” with Abnormal NHCs: Three-Fold Click to Tris-Triazoles
by Nga Kim T. Ho, Sven O. Reichmann, Dennis Rottschäfer, Regine Herbst-Irmer and Rajendra S. Ghadwal
Catalysts 2017, 7(9), 262; https://doi.org/10.3390/catal7090262 - 1 Sep 2017
Cited by 17 | Viewed by 6029
Abstract
Cationic copper(I) complexes [Cu(aIPrPh)(IPr)]I (3) and [Cu(aIPrPh)2]I (4) featuring an abnormal N-heterocyclic carbene (aNHC) (aIPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl- imidazol-4-ylidene) and/or an NHC (IPr = 1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene) ligand(s) are reported. Treatment of Cu(aIPrPh [...] Read more.
Cationic copper(I) complexes [Cu(aIPrPh)(IPr)]I (3) and [Cu(aIPrPh)2]I (4) featuring an abnormal N-heterocyclic carbene (aNHC) (aIPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl- imidazol-4-ylidene) and/or an NHC (IPr = 1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene) ligand(s) are reported. Treatment of Cu(aIPrPh)I (2) with IPr affords complex 3. Reaction of (IPrPh)I (1) (IPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazolium) with CuI in the presence of K{N(SiMe3)2} leads to the formation of 4. Complexes 3 and 4 represent rare examples of mixed aNHC-NHC and bis-aNHC metal complexes, respectively. They are characterized by elemental analysis, NMR spectroscopic, and mass spectrometric studies. The solid-state molecular structures of 3 and 4 have been determined by single crystal X-ray diffraction analyses. The catalytic activity of 2, 3, and 4 has been investigated in the [3+2] cycloaddition of alkynes and organic azides, affording triazole derivatives in an almost quantitative yield. Notably, complexes 2, 3, and 4 are excellent catalysts for the three-fold cycloaddition of a tris-azide with various alkynes. This catalytic protocol offers a high yield access to tris-triazoles in a shorter reaction time and considerably reduces the experimental work-up compared to the classical synthetic method. Full article
(This article belongs to the Special Issue Tailor-Made NHC Ligands)
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4486 KiB  
Article
Enantiopure C1-symmetric N-Heterocyclic Carbene Ligands from Desymmetrized meso-1,2-Diphenylethylenediamine: Application in Ruthenium-Catalyzed Olefin Metathesis
by Veronica Paradiso, Sergio Menta, Marco Pierini, Giorgio Della Sala, Alessia Ciogli and Fabia Grisi
Catalysts 2016, 6(11), 177; https://doi.org/10.3390/catal6110177 - 14 Nov 2016
Cited by 15 | Viewed by 4722
Abstract
In order to design improved chiral ruthenium catalysts for asymmetric olefin metathesis, enantiomeric catalysts incorporating C1-symmetric N-Heterocyclic carbenes (NHC) ligands with syn-related substituents on the backbone were synthesized starting from meso-1,2-diphenylethylenediamine. The absolute configuration of the enantiomers of [...] Read more.
In order to design improved chiral ruthenium catalysts for asymmetric olefin metathesis, enantiomeric catalysts incorporating C1-symmetric N-Heterocyclic carbenes (NHC) ligands with syn-related substituents on the backbone were synthesized starting from meso-1,2-diphenylethylenediamine. The absolute configuration of the enantiomers of the desymmetrized meso diamine was assigned by optical rotation analysis and in silico calculations, and was found to be maintained in their respective ruthenium catalysts by comparison of the relative electronic circular dichroism (ECD) spectra. The catalytic behaviour of the enantiomeric ruthenium complexes was investigated in model asymmetric metathesis transformations and compared to that of analogous complexes bearing C1-symmetric NHC ligands with an anti backbone. Modest enantioselectivities were registered and different catalyst properties depending on the nature of stereochemical relationship of substituents on the backbone were observed. Full article
(This article belongs to the Special Issue Tailor-Made NHC Ligands)
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2110 KiB  
Communication
Olefin Hydroborations with Diamidocarbene–BH3 Adducts at Room Temperature
by Dominika N. Lastovickova and Christopher W. Bielawski
Catalysts 2016, 6(9), 141; https://doi.org/10.3390/catal6090141 - 12 Sep 2016
Cited by 2 | Viewed by 4463
Abstract
An isolable N,N’-diamidocarbene (DAC) was previously shown to promote the B–H bond activation of various BH3 complexes. The resultant DAC–BH3 adducts facilitated olefin hydroborations under mild conditions and in the absence of exogenous initiators. The substrate scope for such transformations [...] Read more.
An isolable N,N’-diamidocarbene (DAC) was previously shown to promote the B–H bond activation of various BH3 complexes. The resultant DAC–BH3 adducts facilitated olefin hydroborations under mild conditions and in the absence of exogenous initiators. The substrate scope for such transformations was further explored and is described herein. While organoboranes were obtained in quantitative yields from various terminal and internal olefins, use of the latter substrates resulted in intramolecular ring-expansion of the newly formed DAC–borane adducts. Full article
(This article belongs to the Special Issue Tailor-Made NHC Ligands)
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Review

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8614 KiB  
Review
Advances in the Knowledge of N-Heterocyclic Carbenes Properties. The Backing of the Electrochemical Investigation
by Marta Feroci, Isabella Chiarotto and Achille Inesi
Catalysts 2016, 6(11), 178; https://doi.org/10.3390/catal6110178 - 16 Nov 2016
Cited by 23 | Viewed by 9288
Abstract
In the last twenty years, N-heterocyclic carbenes (NHCs) have acquired considerable popularity as ligands for transition metals, organocatalysts and in metal-free polymer synthesis. NHCs are generally derived from azolium based salts NHCH+X− by deprotonation or reduction (chemical or electrochemical) [...] Read more.
In the last twenty years, N-heterocyclic carbenes (NHCs) have acquired considerable popularity as ligands for transition metals, organocatalysts and in metal-free polymer synthesis. NHCs are generally derived from azolium based salts NHCH+X− by deprotonation or reduction (chemical or electrochemical) of NHCH+. The extensive knowledge of the physicochemical properties of NHCH+/NHC system could help to select the conditions (scaffold of NHC, nature of the counter-ion X−, solvent, etc.) to enhance the catalytic power of NHC in a synthesis. The electrochemical behavior of NHCH+/NHC system, in the absence and in the presence of solvent, was extensively discussed. The cathodic reduction of NHCH+ to NHC and the anodic oxidation of NHC, and the related effect of the scaffold, solvent, and electrodic material were emphasized. The electrochemical investigations allow acquiring further knowledge as regards the stability of NHC, the acidic and nucleophilic properties of NHCH+/NHC system, the reactivity of NHC versus carbon dioxide and the effect of the hydrogen bond on the catalytic efficiency of NHC. The question of the spontaneous or induced formation of NHC from particular ionic liquids was reconsidered via voltammetric analysis. The results suggested by the classical and the electrochemical methodologies were compared and discussed. Full article
(This article belongs to the Special Issue Tailor-Made NHC Ligands)
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