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

Preface. Hydrogenation Catalysts. Reactors and Reaction Conditions. Hydrogenation of Alkenes. Hydrogenation of Alkynes. Hydrogenation of Aldehydes and Ketones. Preparation of Amines by Reductive Alkylation. Hydrogenation of Nitriles. Hydrogenation of Imines, Oximes, and Related Compounds. Hydrogenation of Nitro, Nitroso, and Related Compounds. Hydrogenation of Carboxylic Acids, Esters, and Related Compounds. Hydrogenation of Aromatic Compounds. Hydrogenation of Heterocyclic Aromatic Compounds. Hydrogenolysis. General Bibliography. Author Index. Subject Index.

Handbook of heterogeneous catalytic hydrogenation for organic synthesis

Virtually all organosulfur compounds react with Fe(0) carbonyls to give the title complexes. These reactions are reviewed in light of major advances over the past few decades, spurred by interest in Fe2(μ-SR)2(CO)x centers at the active sites of the [FeFe]-hydrogenase enzymes. The most useful synthetic route to Fe2(μ-SR)2(CO)6 involves the reaction of thiols with Fe2(CO)9 and Fe3(CO)12. Such reactions can proceed via mono-, di-, and triiron intermediates. The reactivity of Fe(0) carbonyls toward thiols is highly chemoselective, and the resulting dithiolato complexes are fairly rugged. Thus, many complexes tolerate further synthetic elaboration directed at the organic substituents. A second major route involves alkylation of Fe2(μ-S2)(CO)6, Fe2(μ-SH)2(CO)6, and Li2Fe2(μ-S)2(CO)6. This approach is especially useful for azadithiolates Fe2[(μ-SCH2)2NR](CO)6. Elaborate complexes arise via addition of the FeSH group to electrophilic alkenes, alkynes, and carbonyls. Although the first example of Fe2(μ-SR)2(CO)6 ...

Synthesis of Diiron(I) Dithiolato Carbonyl Complexes

A series of new iridium(III) complexes containing bidentate N-heterocyclic carbenes (NHC) functionalized with an alcohol or ether group (NHC?OR, R=H, Me) were prepared. The complexes catalyzed the ...

https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10.1002/chem.201201845

A highly active bifunctional iridium complex with an alcohol/alkoxide-tethered N-heterocyclic carbene for alkylation of amines with alcohols.

While hydrogen plays an ever-increasing role in modern society, nature has utilized hydrogen since a very long time as an energy carrier and storage molecule. Among the enzymatic systems that metabolise hydrogen, [FeFe]-hydrogenases are one of the most powerful systems to perform this conversion. In this light, we will herein present an overview on developments in [FeFe]-hydrogenase research with a strong focus on synthetic mimics and their application within the native enzymatic environment. This review spans from the biological assembly of the natural enzyme and the highly controversial discussed mechanism for the hydrogen generation to the synthesis of multiple mimic platforms as well as their electrochemical behaviour.

[FeFe]-Hydrogenases: maturation and reactivity of enzymatic systems and overview of biomimetic models.

Synthesis and Characterization of Silver(I), Gold(I), and Gold(III) Complexes Bearing Amino-Functionalized N-Heterocyclic Carbenes

Design, synthesis and characterization of a modular bridging ligand platform for bio-inspired hydrogen production

Synthesis and characterization of silver(I), gold(I), and gold(III) complexes bearing a bis-dialkylamino functionalized N -heterocyclic carbene

3-Methyl-1-(2-picolyl)-imidazolium chloride (1) has been synthesized and used as a precursor for the preparation of the (NHC)AgCl complex [NHC = 3-methyl-1-(2-picolyl)imidazol-2-ylidene] (2). Transmetalation of 2 with (tht)AuBr (tht = tetrahydrothiophene) yields the corresponding (NHC)AuBr complex 3, which is further oxidized by Br2 to give the (NHC)AuBr3 compound 4. Treatment of 4 with one equivalent of solid AgBF4 affords the [(NHC)AuBr2][BF4] congener 5 as a pale green, crystalline powder. The structure of 4 and 5 were determined by single-crystal X-ray diffraction, revealing for 5 a κ-N-coordination of the AuIII atom by the picolyl nitrogen atom. Further attempts to exchange all bromides by carboxylates results in the reduction to the dimeric AuI compound [(NHC)2Au2][BF4]2, 6.

Christoph Topf

Papers

Synthesis and Characterization of Silver(I), Gold(I), and Gold(III) Complexes Bearing Amino-Functionalized N-Heterocyclic Carbenes

Design, synthesis and characterization of a modular bridging ligand platform for bio-inspired hydrogen production

Synthesis and characterization of silver(I), gold(I), and gold(III) complexes bearing a bis-dialkylamino functionalized N -heterocyclic carbene

Synthesis and Characterization of Gold(III) Complexes Bearing a Picoline-functionalized N-Heterocyclic Carbene

Group 6 Metal Carbonyl Complexes Supported by a Bidentate PN Ligand: Syntheses, Characterization, and Catalytic Hydrogenation Activity