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.

Self-Assembly of Discrete Cyclic Nanostructures Mediated by Transition Metals

The Cationminus signpi Interaction.

One of the most exciting developments in the areas of catalysis, organometallic chemistry, and polymer science in recent years has been the intense exploration and commercialization of new polymerization technologies based on single-site and metallocene coordination olefin polymerization catalysts.1 The vast number of specifically designed/synthesized transition metal complexes (catalyst precursors) and main-group organometallic compounds (cocatalysts) allows unprecedented control over polymer microstructure, the generation of new polymer architectures, and the development of new polymerization reactions. Commercialization of new generations of single-site and metallocene catalyst-based technologies has provided the multibillion pound per year polyolefins industry with the ability to deliver a wide range of new and innovative olefin-based polymers having improved properties.2-4 The intense industrial activity in the field and the challenges to our basic understanding that have come to light have in turn 1391 Chem. Rev. 2000, 100, 1391−1434

/pdf/cocatalysts-for-metal-catalyzed-olefin-polymerization-37a9jvjiei.pdf

Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure−Activity Relationships

We provide a summary of our results in three-dimensional, coordination-driven self-assembly based on the directional-bonding methodology, in which the stoichiometric mixing of complementary building blocks, with appropriate, predefined geometries, leads to targeted, nanoscopic cages. Using this motif, we have synthesized high-symmetry ensembles resembling the Platonic solids, such as dodecahedra, and the Archimedean solids, such as truncated tetrahedra and cuboctahedra, as well as other cages, like trigonal bipyramids, adamantanoids, and trigonal prisms. The synthesis and characterization of these compounds is discussed, as is some host-guest chemistry.

High-symmetry coordination cages via self-assembly.

Multiple bonds and low coordination in phosphorus chemistry

Nucleophilic carbenes : an incredible renaissance

This book is dedicated to Bernd Eistert, who did so much pioneering work with diazomethane. It is a review in two parts: Properties of Aliphatic Diazo Compounds (four chapters), and Synthesis of Aliphatic Diazo Compounds (12 chapters). Under properties are considered spectroscopy, thermal behavior, reactivity toward acids, and photochemistry. Other types of reactivity, such as the Arndt-Eistert Synthesis, are taken up in a chapter on Substitution Reactions of Diazoalkanes. This book is a rich source of information up to 1982, the termination of the literature coverage. An addendum, subdivided according to chapter, provides a condensed presentation of major developments from 1982 to 1986, but it is not complete and misses a number of things, such as the use of I,I-diacetoxyiodobenzene for oxidizing hydrazones to diazoalkanes. The discussion is in general critical and explanatory. Mechanism is incorporated throughout the text, with a careful distinction between what is established and what is speculative. Abundant, carefully drawn structural formulas contribute to the clarity of the work, and the many tables add to its reference value.

Diazo Compounds: Properties and Synthesis

Organophosphorus compounds have been applied in two ways in chemical synthesis. They can either be used as a reagent in a step of the synthesis (for example, in the Wittig reaction) or they can be incorporated directly into the target molecule. This second application, in particular, has expanded greatly in the last few years with the preparation of low-coordination phosphorus compounds. These include the phosphaalkynes, which are of great interest to organic and inorganic chemists. Phosphaalkynes have been employed in the synthesis of heterocyclic compounds, phosphaarenes and their valence isomers, and polycyclic compounds. Further applications have been the use of phosphaalkynes as new ligand systems in complex chemistry and their cyclooligomerization with organometallic reagents. While the chemical properties of phosphaalkynes have little in common with those of nitriles, they are in many ways very similar to those of the isoelectronic acetylenes.

Phosphaalkynes—Syntheses, Reactions, Coordination Behavior [New Synthetic Methods (73)]†

Organophosphorverbindungen werden auf zweierlei Art in der Synthesechemie eingesetzt: Entweder dienen sie als Hilfsreagentien wie etwa bei der Wittig-Reaktion, oder sie werden selbst in die Zielmolekule eingebaut. Gerade das zweite Anwendungsfeld hat sich durch die Herstellung niederkoordinierter Phosphorverbindungen in den letzten Jahren enorm erweitert. Zu den niederkoordinierten Phosphorverbindungen zahlen auch Phosphaalkine, die im Mittelpunkt dieses Beitrags stehen und viel Interesse sowohl bei Organikern als auch bei Anorganikern gefunden haben. Der Einbau der PCR-Einheit in Heterocyclen, in Phosphaarene und deren Valenzisomere sowie in polycyclische Verbindungen, die Verwendung als neue Ligandensysteme in der Komplexchemie und schlieslich die Cyclooligomerisierung mit Organometallreagentien belegen dies auf eindrucksvolle Weise. Phosphaalkine haben bezuglich ihrer Reaktivitat wenig mit Nitrilen gemeinsam, zeigen aber um so mehr Verwandtschaft mit den isoelektronischen Alkinen.

Manfred Regitz

Papers

Multiple bonds and low coordination in phosphorus chemistry

Nucleophilic carbenes : an incredible renaissance

Diazo Compounds: Properties and Synthesis

Phosphaalkynes—Syntheses, Reactions, Coordination Behavior [New Synthetic Methods (73)]†

Phosphaalkine – Synthesen, Reaktionen, Koordinationsverhalten