N-Heterocyclic carbenes have become universal ligands in organometallic and inorganic coordination chemistry. They not only bind to any transition metal, be it in low or high oxidation states, but also to main group elements such as beryllium, sulfur, and iodine. Because of their specific coordination chemistry, N-heterocyclic carbenes both stabilize and activate metal centers in quite different key catalytic steps of organic syntheses, for example, C-H activation, C-C, C-H, C-O, and C-N bond formation. There is now ample evidence that in the new generation of organometallic catalysts the established ligand class of organophosphanes will be supplemented and, in part, replaced by N-heterocyclic carbenes. Over the past few years, this chemistry has been the field of vivid scientific competition, and yielded previously unexpected successes in key areas of homogeneous catalysis. From the work in numerous academic laboratories and in industry, a revolutionary turning point in oraganometallic catalysis is emerging.

http://aether.cmi.ua.ac.be/artikels/Artikels%20Gitte/Artikels/Reviews/NHC-%20liganden%20Herrmann.pdf

N-heterocyclic carbenes: a new concept in organometallic catalysis.

We have recently described a remarkable new way of exploring packing modes and intermolecular interactions in molecular crystals using a novel partitioning of crystal space. These molecular Hirshfeld surfaces reflect intermolecular interactions in a novel visual manner, offering a hitherto unseen picture of molecular shape in a crystalline environment. The surfaces encode information about all intermolecular interactions simultaneously, but sophisticated interactive graphics are required in order to extract the information most efficiently. To overcome this we have devised a two-dimensional mapping which summarizes quantitatively the nature and type of intermolecular interaction experienced by a molecule in the bulk, and presents it in a convenient graphical format. The mapping takes advantage of the triangulation of the Hirshfeld surfaces, and plots the fraction of points on the surface as a function of the closest distances from the point to nuclei inside and outside the surface.
In this manner all interaction types (for example, hydrogen bonding, close and distant van der Waals contacts, C–H⋯π interactions, π–π stacking) are readily identifiable, and it becomes a straightforward matter to classify molecular crystals by the nature of interactions, and to rapidly identify similarities and differences which can become obscured when examining crystal packing diagrams. These plots are a novel visual representation of all the intermolecular interactions simultaneously, and are unique for a given crystal structure and polymorph. Applications to a wide variety of molecular crystals and intermolecular interactions are presented, including polymorphic systems, as well as crystals where Z′ > 1.

Fingerprinting intermolecular interactions in molecular crystals

and Fuels Changzhi Li,† Xiaochen Zhao,† Aiqin Wang,† George W. Huber,†,‡ and Tao Zhang*,† †State Key Laborotary of Catalysis, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China ‡Department of Chemical and Biological Engineering, University of WisconsinMadison, Madison, Wisconsin 53706, United States

Catalytic Transformation of Lignin for the Production of Chemicals and Fuels

A decade ago we initiated research, the goal of which was isolation of a stable carbene. Our success has helped to catalyze a resurgence of interest in readily available and easily handled carbenes. Research on stable (nucleophilic) carbenes is again a popular theme worldwide. Efforts in the general area of stable carbenes now focus not only on chemistry of the carbenes themselves but also on their applications to other chemical systems, where their chemical properties create technical opportunities that are unavailable with other functional groups. The quest for isolable carbenes is a long saga whose origin can be traced back to the first half of the 1800s. A recently published history of this quest provides an important backdrop for the research described in this Account.1 It is the intent of this Account to delineate the events and environment that led to the report from DuPont laboratories of the first isolation of a stable crystalline carbene. Getting Started

Looking for Stable Carbenes: The Difficulty in Starting Anew

3. Soluble Metal Oxides 2459 3.1. Polyoxometalates 2459 3.2. Peroxotungstates 2459 3.3. Peroxomolybdates 2460 3.4. Methyltrioxorhenium 2461 3.5. Other Metal Oxides 2461 4. Metal Oxides Generated in Situ 2461 4.1. Selenium and Arsenic Compounds 2461 4.2. Simple Metal Salts 2462 5. Coordination Complexes 2463 5.1. Manganese Porphyrins 2463 5.2. Iron Porphyrins 2464 5.3. Manganese Salen Complexes 2466 5.4. 1,4,7-Triazacyclononane (TACN) Complexes 2466 5.5. Iron and Manganese Pyridyl-Amine Complexes 2468

/pdf/metal-catalyzed-epoxidations-of-alkenes-with-hydrogen-3kxbglgruw.pdf

Metal-Catalyzed Epoxidations of Alkenes with Hydrogen Peroxide

Stable Cyclic Germanediyls (“Cyclogermylenes”): Synthesis, Structure, Metal Complexes, and Thermolyses

Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen: CXXVI. Heterocyclen-Carbene als phosphananaloge Liganden in Metallkomplexen

Methyltrioxorhenium(VII) as Catalyst for Epoxidations: Structure of the Active Species and Mechanism of Catalysis

Stabile, cyclische Germandiyle („Cyclogermylene”︁): Herstellung, Molekülstruktur, Metallkomplexe und Thermolysen

Pyrazole and pyridine adducts of methyltrioxorhenium(VII) form bisperoxo complexes with excess H2O2 (see picture). Density functional calculations reveal that the increased efficiency of these complexes as catalysts for olefin epoxidation originates from their stability and from the moderate energies of the corresponding transition states. Nonaromatic nitrogen-base ligands reduce the catalytic performance of the adducts, in agreement with the computational results.

Trigonal-Bipyramidal Lewis Base Adducts of Methyltrioxorhenium(VII) and Their Bisperoxo Congeners: Characterization, Application in Catalytic Epoxidation, and Density Functional Mechanistic Study

Wolfgang Scherer

Papers

Stable Cyclic Germanediyls (“Cyclogermylenes”): Synthesis, Structure, Metal Complexes, and Thermolyses

Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen: CXXVI. Heterocyclen-Carbene als phosphananaloge Liganden in Metallkomplexen

Methyltrioxorhenium(VII) as Catalyst for Epoxidations: Structure of the Active Species and Mechanism of Catalysis

Stabile, cyclische Germandiyle („Cyclogermylene”︁): Herstellung, Molekülstruktur, Metallkomplexe und Thermolysen

Trigonal-Bipyramidal Lewis Base Adducts of Methyltrioxorhenium(VII) and Their Bisperoxo Congeners: Characterization, Application in Catalytic Epoxidation, and Density Functional Mechanistic Study