Abstracts

2.1.1 Historical Overview of N-Heterocyclic Carbenes in Alkene Metathesis

C. Slugovc

This chapter is a short outline of the historic development of the use of N-heterocyclic carbenes as co-ligands in alkene metathesis catalysts.

Keywords: alkene metathesis • N-heterocyclic carbenes • alkenes • ruthenium • molybdenum

2.1.2 Ring-Closing Metathesis

J. Broggi and H. Clavier

This chapter describes the use of ruthenium alkylidene complexes bearing N-heterocyclic carbene ligands as catalysts for the preparation of cyclic compounds (from 5- to 33-membered rings) by metathesis. Also included are examples of asymmetric metathesis using catalysts bearing chiral N-heterocyclic carbenes.

Keywords: alkenes • asymmetric catalysis • N-heterocyclic carbenes • carbon–carbon double bonds • cycloalkenes • metal–carbene complexes • metathesis • ring closure • ring formation • cyclization • ruthenium catalysts

2.1.3 Cross Metathesis

A. Jana, P. Małecki, and K. Grela

During the past two decades, among all the types of transition-metal-catalyzed reaction, olefin metathesis has become arguably the most powerful synthetic tool for carbon–carbon bond formation. The reason for this is undoubtedly the development of well-defined functional-group-tolerant N-heterocyclic carbene (NHC) based ruthenium alkylidene catalysts. Among the types of olefin metathesis, cross metathesis is probably the most useful due to its numerous advantages and has found a wide range of application in almost every field of organic synthesis. Introduction of NHCs has made the ruthenium catalysts more stable and more functional group tolerant. The efficiency and selectivity of the reaction and the activity of the catalyst are three key issues that need to be considered in cross metathesis and introduction of NHC-based ruthenium catalysts addresses all three. This chapter focuses on different types of cross metathesis, performed under different conditions and using different NHC-based catalysts.

Keywords: alkenes • metathesis • N-heterocyclic carbenes • ruthenium • ethenolysis • carbon–carbon double bonds • carbenes • ligands • metal–carbene complex • isomerization • asymmetric • oleochemistry • selectivity

2.1.4 Enyne Metathesis

C. E. Diesendruck

Enyne metathesis is a metal-catalyzed reaction between an alkene and an alkyne, resulting in C-C bond formation to give a 1,3-diene. This chapter explores the different forms of this powerful reaction, both as a single reaction and as part of a reaction cascade to form polycyclic compounds.

Keywords: metathesis • carbon-carbon bond formation • enynes • dienes • cyclization • polycyclic compounds • cascade reactions • metallacycles • N-heterocyclic carbenes

2.1.5 Alkene Metathesis Based Polymerization

J. Liu and J. A. Johnson

Alkene metathesis based polymerizations that rely on metal complexes with N-heterocyclic carbene (NHC) ligands are discussed in this chapter. Particular emphasis is placed on novel polymer microstructures, architectures, and applications that have been enabled by NHC–metal complexes. Applications of ruthenium–NHC initiated ring opening metathesis polymerization (ROMP) for the synthesis of block copolymers, branched polymers, stereocontrolled polymers, and cyclic polymers are described. Ruthenium–NHC catalyzed acyclic diene metathesis polymerization (ADMET) and cyclopolymerization are also discussed, along with alkene metathesis polymerizations using tungsten–and molybdenum–NHC complexes.

Keywords: N-heterocyclic carbenes • alkene metathesis • polymer chemistry • ring opening metathesis polymerization • acyclic diene metathesis polymerization • cyclopolymerization • living polymerization • metal initiators • bottlebrush polymers • tacticity • star polymers • surface grafting • aqueous polymerization • stereocontrolled polymers • sequence-controlled polymers • alternating copolymers

2.2 Polymerization, Oligomerization, and Telomerization Involving N-Heterocyclic Carbenes as Ligands or Initiators

C. Costabile

This chapter is an overview of recent developments in polymerization and oligomerization of alkenes and cyclic esters involving N-heterocyclic carbenes, both as ligands in organometallic catalysts and as organocatalysts. Telomerization reactions catalyzed by Nheterocyclic carbene–palladium complexes are also briefly discussed.

Keywords: polymerization • oligomerization • telomerization • organocatalysis • ethene • styrene • norbornene • conjugated dienes • cyclic esters • N-heterocyclic carbenes

2.3 Cyclization Reactions

Y. Zhong, S. Felten, and J. Louie

This chapter presents a detailed overview of current research into N-heterocyclic carbene (NHC) coordinated, transition-metal-catalyzed cyclization reactions. Highly efficient and economical access to pharmacologically relevant moieties, such as carbo- and heterocycles, is crucial in synthetic chemistry. Though cyclizations are atom-economical, historically harsh reaction conditions, poor substrate tolerance, and low product selectivity severely limited the practicality of such reactions. However, transition-metal catalysts based on copper, gold, palladium, nickel, rhodium, cobalt, and iron have allowed for the rapid synthesis of cyclization products in good to high yield and with high selectivity. In addition, these cyclizations tolerate starting materials bearing a variety of functional groups. Symmetric and asymmetric NHC ligands have proven to be critical for success in generating efficient transition-metal based catalytic systems. The electronic and steric diversity of NHC ligands allows for the fine-tuning of the transition-metal catalyst, which has resulted in effective [n + m]-cycloaddition reactions, inter- and intramolecular cycloisomerization reactions, and rearrangement reactions.

Keywords: cobalt catalysis • copper catalysis • cyclization • cycloaddition • cycloisomerization • gold catalysis • iron catalysis • N-heterocyclic carbenes • nickel catalysis • palladium catalysis • rearrangements • rhodium catalysis • transition-metal catalysis

2.4 N-Heterocyclic Carbenes in Asymmetric Transition-Metal Catalysis

S. K. Collins and M. Holtz-Mulholland

Catalytic asymmetric reactions catalyzed by chiral N-heterocyclic carbene (NHC) complexes have become an important synthetic tool for the synthesis of key chiral building blocks. This chapter describes the different NHC ligand types that have been developed, including both monodentate/bidentate and C1- and C2-symmetric ligands. In addition, the use of such ligands in a variety of asymmetric transformations is presented, as well as applications in the construction of complex molecules.

Keywords: asymmetric reactions • hydroboration • hydrosilylation • metathesis • N-heterocyclic carbenes • nickel catalysis • transition-metal catalysis

2.5 Transition-Metal-Catalyzed Oxidations

D. Munz

The use of transition-metal complexes with N-heterocyclic carbene (NHC) ligands for oxidative catalysis is summarized in this chapter. Special attention is given to the applicability in organic synthesis and the comparison of results for different reaction conditions and catalyst types. The stoichiometric reactivity of NHC–transition-metal complexes (Ru, Co, Ir, Ni, Pd) with molecular oxygen and the stabilization of high-valent metal complexes with chelating ligands are discussed. The oxidation of alcohols to aldehydes and ketones, Wacker-type oxidation, aziridination and epoxidation of olefins, oxidative scission of alkenes to aldehydes, and oxidation of saturated and aromatic hydrocarbons are addressed.

Keywords: oxidation • N-heterocyclic carbenes • ligands • catalysis • oxygen • metal • transition-metal complexes • alcohols • alkenes • hydrocarbons • aromatics • aziridination • epoxidation • alkene scission

2.6 Carboxylation, Carbonylation, and Dehalogenation

D. J. Nelson

This chapter describes the use of N-heterocyclic carbene–metal complexes in carboxylation, carbonylation, and dehalogenation reactions. Catalysts based on copper, gold, palladium, rhodium, and nickel are considered.

Keywords: carboxylation • carbonylation • dehalogenation • carboxylic acids • esters • amides • carbonyl compounds • carbon monoxide • carbon dioxide • cross coupling • N-heterocyclic carbene–metal complexes • copper • gold • palladium • rhodium • nickel

2.7.1 Biphasic Systems

C. Claver, C. Godard, and A. Martínez...