It is well-recognized that N-heterocyclic carbene (NHC) ligands have provided a new dimension to the design of homogeneous catalysts. Part of the success of this type of ligands resides in the limitless access to a variety of topologies with tuned electronic properties, but also in the ability of a family of NHCs that are able to adapt their properties to the specific requirements of individual catalytic transformations. The term “smart” is used here to refer to switchable, multifunctional, adaptable, or tunable ligands and, in general, to all those ligands that are able to modify their steric or electronic properties to fulfill the requirements of a defined catalytic reaction. The purpose of this review is to comprehensively describe all types of smart NHC ligands by focusing attention on the catalytically relevant ligand-based reactivity.

Smart N-Heterocyclic Carbene Ligands in Catalysis

The ruthenium-catalyzed azide alkyne cycloaddition (RuAAC) affords 1,5-disubstituted 1,2,3-triazoles in one step and complements the more established copper-catalyzed reaction providing the 1,4-isomer. The RuAAC reaction has quickly found its way into the organic chemistry toolbox and found applications in many different areas, such as medicinal chemistry, polymer synthesis, organocatalysis, supramolecular chemistry, and the construction of electronic devices. This Review discusses the mechanism, scope, and applications of the RuAAC reaction, covering the literature from the last 10 years.

https://research.chalmers.se/publication/246752/file/246752_Fulltext.pdf

Ruthenium-Catalyzed Azide Alkyne Cycloaddition Reaction: Scope, Mechanism, and Applications.

Recent developments in penta-, hexa- and heptadentate Schiff base ligands and their metal complexes

https://hal-univ-rennes1.archives-ouvertes.fr/hal-01282461/document

Metal-Catalyzed Azide-Alkyne “Click” Reactions: Mechanistic Overview and Recent Trends

Hydrolysis of ammonia borane (AB) is a very convenient source of H2, but this reaction needs catalytic activation to become practical under ambient conditions. Here this reaction is catalyzed by bimetallic late transition-metal nanoparticles (NPs) that are stabilized and activated by “click” dendrimers. Dendrimers 1 and 2 contain 27 or 81 triethylene glycol terminal groups and 9 or 27 1,2,3-triazole ligands, respectively, located on the dendritic tethers. A remarkable synergy between Pt and Co in the Pt–Co/“click” dendrimer nanocatalysts is revealed. These Pt–Co/“click” dendrimer catalysts are much more efficient for hydrolysis of AB than either “click” dendrimer-stabilized Co or Pt analogues alone. The best catalyst, Pt1Co1/1, stabilized by the nonatriazole “click” dendrimer 1 achieves a turnover frequency number (TOF) of 303 molH2 molcat–1 min–1 (606 molH2 molPt–1 min–1) at 20 ± 1 °C. The AB hydrolysis reaction catalyzed by Pt1Co1/1 is boosted by NaOH, the TOF value reaching 476.2 molH2 molcat–1 min–1 (952.4 molH2 molPt–1 min–1), one of the very best results ever obtained for this reaction. The presence of ≥25% Pt in the CoPt nanoalloy provides a reaction rate higher than that obtained with the pure PtNP catalyst alone. The kinetics involves in particular a kinetic isotope effect kD/kH of 2.46 obtained for the hydrolysis reaction with D2O, suggesting that an O–H bond of water is cleaved in the rate-determining step. Tandem reactions were carried out for the hydrogenation of styrene with hydrogen generated from the hydrolysis of AB. Performing this tandem reaction with D2O shows deuteration of the ethylbenzene products, confirming O–D bond cleavage and H/D scrambling on the bimetallic NP surface. Finally, a full reaction mechanism is proposed. This dramatic synergy type should also prove to be useful in a number of other catalytic systems.

/pdf/dramatic-synergy-in-copt-nanocatalysts-stabilized-by-click-4ldpnk8od5.pdf

Dramatic synergy in CoPt nanocatalysts stabilized by "click" dendrimers for evolution of hydrogen from hydrolysis of ammonia borane

https://hal-univ-rennes1.archives-ouvertes.fr/hal-01208404/document

Reaction mechanisms of transition-metal-catalyzed azide–alkyne cycloaddition “click” reactions: A DFT investigation

A series of clusters of the form [Et4N][Fe2(CO)6(μ3-As)}(μ3-EFe(CO)4)], where E is either P or As, were synthesized from [Et4N]2[HAs{Fe(CO)4}3] and ECl3. AsCl3 gives the As-only compound; PCl3 produces compounds having two As atoms with one P atom, or one As atom and two P atoms, and they can exist as two possible isomers, one of which is chiral. The As2P and AsP2 clusters cocrystallize, and their structure as determined by single-crystal X-ray diffraction is given along with the structure of the As-only cluster. Analytical data as well as density functional theory calculations support the formation and geometries of the new molecules.

/pdf/new-main-group-element-rich-nido-octahedral-cluster-system-ktx5a6tcg7.pdf

New Main-Group-Element-Rich nido-Octahedral Cluster System: Synthesis and Characterization of [Et4N][Fe2(CO)6(μ3-As){μ3-EFe(CO)4}2].

This review is focused on the mechanistic aspects and recent trends of the metal-catalyzed azide-alkyne cycloaddition (MAAC) so-called “click” reactions with catalysts based on various metals (Cu, Ru, Ag, Au, Ir, Ni, Zn, Ln), although Cu (I) catalysts are still the most used ones. These MAAC reactions are by far the most common click reactions relevant to the “green chemistry” concept. First developed by the Fokin-Sharpless and Meldal group with Cu(I) in 2002, they have then been extended to Ru(II) catalysts by the Fokin group in 2005 and finally to many other metal catalysts. Mechanistic investigations are essential to reaction improvements and subsequent applications, and indeed as shown in this review the proposed mechanisms have been multiple during the last decade based on theoretical computations and experimental search of intermediates. New trends (since 2012) are also presented here often representing both exciting approaches for various applications and new challenges for further mechanistic investigations

Djamila Ikhlef

Papers

Metal-Catalyzed Azide-Alkyne “Click” Reactions: Mechanistic Overview and Recent Trends

Reaction mechanisms of transition-metal-catalyzed azide–alkyne cycloaddition “click” reactions: A DFT investigation

New Main-Group-Element-Rich nido-Octahedral Cluster System: Synthesis and Characterization of [Et4N][Fe2(CO)6(μ3-As){μ3-EFe(CO)4}2].

Metal‐Catalyzed Azide‐Alkyne “Click” Reactions: Mechanistic Overview and Recent Trends