Titelei 213v2 1. - Thieme€¦ · Keywords: oxidation • N-heterocyclic carbenes • ligands • catalysis • oxygen • metal • tran-sition-metal complexes • alcohols • alkenes

Abstracts

p 12.1.1 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 car-benes as co-ligands in alkene metathesis catalysts.

NN

Ru

ButCOO

Mes

OPriN N

NNPri Pri

PriPri

RuPhCl

Cl

(1998) (2011)

Keywords: alkene metathesis • N-heterocyclic carbenes • alkenes • ruthenium • molybde-num

p 112.1.2 Ring-Closing Metathesis

J. Broggi and H. Clavier

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

N N

LnRu

Ar1

R1 R2

H2C CH2−

5- to 33-membered rings

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

p 472.1.3 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–car-bon bond formation. The reason for this is undoubtedly the development of well-definedfunctional-group-tolerant N-heterocyclic carbene (NHC) based ruthenium alkylidene cat-alysts. Among the types of olefin metathesis, cross metathesis is probably the most useful

XI

Science of Synthesis Reference Library N-Heterocyclic Carbenes in Catalytic Organic Synthesis Volume 2 © Georg Thieme Verlag KG

due to its numerous advantages and has found a wide range of application in almost everyfield of organic synthesis. Introduction of NHCs has made the ruthenium catalysts morestable and more functional group tolerant. The efficiency and selectivity of the reactionand the activity of the catalyst are three key issues that need to be considered in cross me-tathesis and introduction of NHC-based ruthenium catalysts addresses all three. Thischapter focuses on different types of cross metathesis, performed under different condi-tions and using different NHC-based catalysts.

R2R1 R1

R2+NHC-based ruthenium catalyst

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

asymmetric • oleochemistry • selectivity

p 792.1.4 Enyne Metathesis

C. E. Diesendruck

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

O

O

O

O

O

O

O

O

OO

Ru

PCy3

Cl

Cl Ph

NN MesMes

CH2Cl2, 40 °C, 4 h

51%(5 mol%)

Keywords: metathesis • carbon-carbon bond formation • enynes • dienes • cyclization •

polycyclic compounds • cascade reactions • metallacycles • N-heterocyclic carbenes

XII Abstracts


p 992.1.5 Alkene Metathesis Based Polymerization

J. Liu and J. A. Johnson

Alkene metathesis based polymerizations that rely on metal complexes with N-heterocy-clic carbene (NHC) ligands are discussed in this chapter. Particular emphasis is placed onnovel polymer microstructures, architectures, and applications that have been enabledby NHC–metal complexes. Applications of ruthenium–NHC initiated ring opening me-tathesis polymerization (ROMP) for the synthesis of block copolymers, branched poly-mers, stereocontrolled polymers, and cyclic polymers are described. Ruthenium–NHCcatalyzed acyclic diene metathesis polymerization (ADMET) and cyclopolymerization arealso discussed, along with alkene metathesis polymerizations using tungsten– and mo-lybdenum–NHC complexes.

n

Xn

Xn

M

NN R1

R2

X X X X X X

functional polymers

R1

n−5

X

Keywords: N-heterocyclic carbenes • alkene metathesis • polymer chemistry • ring open-ing metathesis polymerization • acyclic diene metathesis polymerization • cyclopolymer-ization • living polymerization • metal initiators • bottlebrush polymers • tacticity • starpolymers • surface grafting • aqueous polymerization • stereocontrolled polymers • se-quence-controlled polymers • alternating copolymers

p 1272.2 Polymerization, Oligomerization, and Telomerization Involving N-Heterocyclic

Carbenes as Ligands or InitiatorsC. Costabile

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

N-heterocyclic carbene

NHC organocatalyst NHC−metalcomplex

telomerizationcyclic esterpolymerization

alkenepolymerization

Keywords: polymerization • oligomerization • telomerization • organocatalysis • ethene •

styrene • norbornene • conjugated dienes • cyclic esters • N-heterocyclic carbenes

Abstracts XIII


p 1512.3 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 andeconomical access to pharmacologically relevant moieties, such as carbo- and heterocy-cles, is crucial in synthetic chemistry. Though cyclizations are atom-economical, histori-cally harsh reaction conditions, poor substrate tolerance, and low product selectivity se-verely limited the practicality of such reactions. However, transition-metal catalystsbased on copper, gold, palladium, nickel, rhodium, cobalt, and iron have allowed for therapid synthesis of cyclization products in good to high yield and with high selectivity. Inaddition, these cyclizations tolerate starting materials bearing a variety of functionalgroups. Symmetric and asymmetric NHC ligands have proven to be critical for success ingenerating efficient transition-metal based catalytic systems. The electronic and steric di-versity of NHC ligands allows for the fine-tuning of the transition-metal catalyst, whichhas resulted in effective [n + m]-cycloaddition reactions, inter- and intramolecular cyclo-isomerization reactions, and rearrangement reactions.

X

X

R3

R4

R5

X

OR3

R4

R3

R4

O

R7

R4

R5

R6

NX

R3

R4

R5

NH

N

O

R3

R4

R5

R6

O

R3

R4

R6 R5

X = O, NTs

R7

MeO2C

MeO2C

R3

R4

R5

R6

R5

M

Ln

NNR1 R2

R3

Keywords: cobalt catalysis • copper catalysis • cyclization • cycloaddition • cycloisomeri-zation • gold catalysis • iron catalysis • N-heterocyclic carbenes • nickel catalysis • palladiumcatalysis • rearrangements • rhodium catalysis • transition-metal catalysis

XIV Abstracts


p 2292.4 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) com-plexes have become an important synthetic tool for the synthesis of key chiral buildingblocks. This chapter describes the different NHC ligand types that have been developed,including both monodentate/bidentate and C1- and C2-symmetric ligands. In addition, theuse of such ligands in a variety of asymmetric transformations is presented, as well as ap-plications in the construction of complex molecules.

N NX∗ X∗

[M]N N

[M]

or

R3 R4

R1 R2

X∗ = chirality-inducing group

∗ ∗

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

p 2652.5 Transition-Metal-Catalyzed Oxidations

D. Munz

The use of transition-metal complexes with N-heterocyclic carbene (NHC) ligands for oxi-dative catalysis is summarized in this chapter. Special attention is given to the applicabil-ity in organic synthesis and the comparison of results for different reaction conditionsand 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 complexeswith chelating ligands are discussed. The oxidation of alcohols to aldehydes and ketones,Wacker-type oxidation, aziridination and epoxidation of olefins, oxidative scission of al-kenes to aldehydes, and oxidation of saturated and aromatic hydrocarbons are addressed.

R3 R4

R5 H

R5 OH

OR7

R6R7

R6

R8NR7

R6

O

R3 R4

OH

R6 H

OR7

R6

O

N N R2R1

MLn

alkanes

alkenes

alcohols

M = Pd, Ir; [O]M = Pd; [O]

M = Fe, Ru, Ir, Pd; [O], NR8

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

Abstracts XV


p 2812.6 Carboxylation, Carbonylation, and Dehalogenation

D. J. Nelson

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

B

1. CuCl(IPr) (1 mol%), CO2 (1 atm)

KOt-Bu (1.05 equiv), THF, reflux, 24 h

2. aq HCl

O

OH

O

O

Bz

Bz99%

{PdCl(μ-Cl)(IPr)}2 (400 pm)

KOt-Bu or NaOH (4.4 equiv)

iPrOH, 80 oC, 24 hCl

ClCl

Cl

100% conversion

I

CuI(IPr) (1 mol%)

IPr•HCl (2 mol%)

CO (30 atm), Cs2CO3 (2 equiv)

1,4-dioxane, 100 oC, 10 h

O

N

O

+92%

O

O

HN

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

XVI Abstracts


p 2972.7.1 Biphasic Systems

C. Claver, C. Godard, and A. Mart�nez Lombard�a

To overcome the inherent issue of catalyst recycling in homogeneous catalysis, much ef-fort has been devoted to the heterogenization of catalysts onto solid supports and to theseparation of the reactants (and/or products) and the catalyst using immiscible liquidphases (liquid multiphase catalysis). For these latter systems, solvents such as water, alco-hols, ionic liquids, fluorous media, supercritical fluids, and gas-expanded liquids havebeen employed successfully as the catalyst phase. In this chapter, the most relevant bi-phasic catalytic systems involving NHC complexes are discussed. Particular attention isdevoted to alkene metathesis, which is considered to be one of the most important pro-cesses that uses complexes with carbene ligands. Sulfonated or related water-soluble car-bene ligands are also described for biphasic reactions, such as cyclization, C-C bond for-mation, and hydroformylation.

metathesis products

ionic liquid

alkenes

Ru

NN MesMes

O

O

O

Pri

OMe2N

Me2N

NMe2 2BF4−

2+

NR3+ X−

NR3+ X−

NR3+ X−

−X +R3N

Keywords: biphasic • N-heterocyclic carbene complexes • catalyst recycling • catalysts •

hydroformylation • metathesis • solvents • supported catalysis

Abstracts XVII


p 3092.7.2 Covalently Immobilized N-Heterocyclic Carbene Complexes

C. Thieuleux and D. Crozet

This chapter focuses on the preparation and the catalytic performance of metal–NHCcomplexes immobilized on oxide supports, which are designed so that the metal–NHCcomplex is maintained on the support during catalysis. The major scientific contributionsfor the covalent immobilization of metal–NHC complexes onto various oxides are cov-ered, with an emphasis on the most distinguished examples. Particular attention is direct-ed toward the anchoring of metal complexes via the substituents or the backbone of theNHC ligand, or via another X/L-type ligand that is not expected to suffer from decoordina-tion during the catalytic process.

support

N NR1 R2

M

R3

ligand Ln

Xm

organiclinker

organiclinker

N N R2

M

R3

ligand Ln

Xm

organiclinker

NN

R1

R2

R3

Mligand Ln

Xm

organic

linker

N

N

R1

R2

M

ligand

Ln

Xm

Keywords: N-heterocyclic carbene complexes • supported catalysts • grafting • immobili-zation • oxides • sol-gel process • catalysis

XVIII Abstracts


p 3512.7.3 Catalytic Systems Featuring Ionically Tagged N-Heterocyclic Carbene Ligands

T. E. Schmid, C. Cr�visy, O. Basl�, and M. Mauduit

Since the discovery of N-heterocyclic carbenes (NHCs), their unique properties as ligandsin organometallic chemistry have enabled the synthesis of a myriad of novel metal com-plexes. Thanks to the facile modulation of this class of ligands, they can be easily func-tionalized with ionic tags, which has proven to be useful for various applications. Nota-bly, such groups have enabled the immobilization of metal complexes on a variety of sup-ports, and recyclable catalysis could be realized. This chapter describes organometallicspecies featuring ionically-tagged NHCs for such applications, focusing on catalytic sys-tems that show the best performance in terms of versatility and reusability.

ionic liquid,

water,

silica,

or resinsN NAr1 Ar2

R2R1

ionic tag

MLn

• immobilization

• aqueous catalysis

• catalyst recycling

• catalyst recovery

• cross coupling

• alkene metathesis

• click chemistry

• hydrosilylation

• hydrogenation

• isomerization

Keywords: N-heterocyclic carbenes • metal–carbene complexes • catalysts • supportedcatalysis • alkene metathesis • cross-coupling reactions • hydrogenation • hydrosilylation

p 3692.7.4 Flow Systems for N-Heterocyclic Carbene Catalysis

I. PeÇafiel and A. Lapkin

Continuous-flow technology represents a paradigm shift in the manufacture of specialtychemicals and pharmaceuticals. In many such syntheses, catalysis by N-heterocyclic car-benes plays an important role due to the stability, activity, and broad synthetic utility ofthese species. This chapter explores the “sweet-spot” in the combination of catalysis byN-heterocyclic carbenes and flow-chemistry technology. The chapter opens with a de-scription of the fundamentals of flow technology and then relates the functions of flowreactors to the specifics of N-heterocyclic carbene based catalysis. The chapter providesan overview of up-to-date literature on catalysis by carbenes in flow reactors.

Keywords: continuous flow • flow chemistry • process intensification • N-heterocycliccarbenes • heterogenized catalysts

Abstracts XIX


p 3952.8 Recent Advances in N-Heterocyclic Carbene Organocatalysis

A. T. Davies and A. D. Smith

In recent years, organocatalysis has seen a rapid rise in popularity and this has led to asubsequent increase in the research output of the area, with organocatalysis by N-hetero-cyclic carbenes (NHCs) playing a significant role. Beginning with the benzoin condensa-tion, through the work of Breslow and others to modern, asymmetric protocols, NHC or-ganocatalysis has a rich history, which has been covered in many reviews. The focus ofthis chapter is on recent advances within the area of NHC organocatalysis, offering a briefhistorical perspective and highlighting what the authors believe to be some of the key ad-vances made within recent times, both in terms of novel processes and significant ad-vancements on previously documented reactions.

THF, 66 oC, 14 h

N

N N But

O

Bn

O O

Ph

EtO2C

O

OPh

EtO2C

71%; dr >20:1; er 98:2

(20 mol%)

Keywords: organocatalysis • N-heterocyclic carbenes • azolium enolates • acyl azoliums •

acyl anions • Breslow intermediate

XX Abstracts


Documents

Titelei 213v2 1. - Thieme€¦ · Keywords: oxidation • N-heterocyclic carbenes • ligands • catalysis • oxygen • metal • tran-sition-metal complexes • alcohols • alkenes