Iron Catalysis in Organic Chemistry

Reactions and Applications

Edited byBernd Plietker

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Iron Catalysis in Organic Chemistry

Edited by

Bernd Plietker

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Iron Catalysis in Organic Chemistry

Reactions and Applications

Edited byBernd Plietker

The Editor

Prof. Dr. Bernd PlietkerInstitut für Organische ChemieUniversität StuttgartPfaffenwaldring 5570569 StuttgartGermany

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Contents

Preface XIList of Contributors XIII

1 Iron Complexes in Organic Chemistry 1Ingmar Bauer and Hans-Joachim Knölker

1.1 Introduction 11.2 General Aspects of Iron Complex Chemistry 21.2.1 Electronic Configuration, Oxidation States, Structures 21.2.2 Fundamental Reactions 21.3 Organoiron Complexes and Their Applications 41.3.1 Binary Carbonyl–Iron Complexes 51.3.2 Alkene–Iron Complexes 71.3.3 Allyl– and Trimethylenemethane–Iron Complexes 81.3.4 Acyl– and Carbene–Iron Complexes 91.3.5 Diene–Iron Complexes 111.3.6 Ferrocenes 181.3.7 Arene–Iron Complexes 181.4 Catalysis Using Iron Complexes 201.4.1 Iron Complexes as Substrates and/or Products in Catalytic

Reactions 201.4.2 Iron Complexes as Ligands for Other Transition Metal Catalysts 211.4.3 Iron Complexes as Catalytically Active Species 21

References 24

2 Iron Catalysis in Biological and Biomimetic Reactions 292.1 Non-heme Iron Catalysts in Biological and Biomimetic

Transformations 29Jens Müller

2.1.1 Introduction: Iron in Biological Processes 292.1.2 Non-heme Iron Proteins 302.1.2.1 Mononuclear Iron Sites 30

V

2.1.2.2 Dinuclear Iron Sites 392.1.3 Summary 45

References 46

2.2 Organic Reactions Catalyzed by Heme Proteins 48Martin Bröring

2.2.1 Classification and General Reactivity Schemes of Heme ProteinsUsed in Organic Synthesis 48

2.2.2 Organic Reactions Catalyzed by Cytochromes P450 512.2.3 Organic Reactions Catalyzed by Heme Peroxidases 562.2.3.1 Dehydrogenations (‘‘Peroxidase Reactivity’’) 562.2.3.2 Sulfoxidations (‘‘Peroxygenase Reactivity’’) 572.2.3.3 Peroxide Disproportionation (‘‘Catalase Reactivity’’) 582.2.3.4 Halogenation (‘‘Haloperoxidase Reactivity’’) 612.2.3.5 Epoxidations (‘‘Monoxygenase Activity’’) 62

References 66

3 Iron-catalyzed Oxidation Reactions 733.1 Oxidations of C–H and C¼C Bonds 73

Agathe Christine Mayer and Carsten Bolm3.1.1 Gif Chemistry 733.1.2 Alkene Epoxidation 803.1.3 Alkene Dihydroxylation 823.1.4 The Kharasch Reaction and Related Reactions 843.1.5 Aziridination and Diamination 87

References 89

3.2 Oxidative Allylic Oxygenation and Amination 92Sabine Laschat, Volker Rabe, and Angelika Baro

3.2.1 Introduction 923.2.2 Iron-catalyzed Allylic Oxidations 933.2.2.1 Simple Iron Salts 933.2.2.2 Fe(III) Complexes with Bidentate Ligands 943.2.2.3 Fe3þ/Fe2þ Porphyrin and Phthalocyanine Complexes 953.2.2.4 Iron(III) Salen Complexes 1003.2.2.5 Non-heme Iron Complexes with Tetra- and Pentadentate

Ligands 1003.2.3 Oxidative Allylic Aminations 1033.2.4 Conclusion 107

References 107

3.3 Oxidation of Heteroatoms (N and S) 109Olga García Mancheño and Carsten Bolm

3.3.1 Oxidation of Nitrogen Compounds 109

VI Contents

3.3.1.1 Oxidation of Hydroxylamines to Nitroso Compounds 1093.3.1.2 Oxidation of Arylamines 1103.3.1.3 Other N-Oxidations 1103.3.2 Oxidation of Sulfur Compounds 1113.3.2.1 Oxidation of Thiols to Disulfides 1113.3.2.2 Oxidation of Sulfides 1133.3.2.3 Oxidative Imination of Sulfur Compounds 119

References 122

4 Reduction of Unsaturated Compounds with HomogeneousIron Catalysts 125Stephan Enthaler, Kathrin Junge, and Matthias Beller

4.1 Introduction 1254.2 Hydrogenation of Carbonyl Compounds 1254.3 Hydrogenation of Carbon–Carbon Double Bonds 1294.4 Hydrogenation of Imines and Similar Compounds 1364.5 Catalytic Hydrosilylations 1364.6 Conclusion 141

References 142

5 Iron-catalyzed Cross-coupling Reactions 147Andreas Leitner

5.1 Introduction 1475.2 Cross-coupling Reactions of Alkenyl Electrophiles 1475.3 Cross-coupling Reactions of Aryl Electrophiles 1545.4 Cross-coupling Reactions of Alkyl Electrophiles 1615.5 Cross-coupling Reactions of Acyl Electrophiles 1685.6 Iron-catalyzed Carbometallation Reactions 1705.7 Conclusion 172

References 173

6 Iron-catalyzed Aromatic Substitutions 177Jette Kischel, Kristin Mertins, Irina Jovel, Alexander Zapf, and Matthias Beller

6.1 General Aspects 1776.2 Electrophilic Aromatic Substitutions 1786.2.1 Halogenation Reactions 1786.2.2 Nitration Reactions 1796.2.3 Sulfonylation Reactions 1806.2.4 Friedel–Crafts Acylations 1816.2.5 Friedel–Crafts Alkylations 1836.2.5.1 Alkylation with Alcohols, Ethers and Esters 1846.2.5.2 Alkylation with Alkenes 1866.3 Nucleophilic Aromatic Substitutions 188

References 191

Contents VII

7 Iron-catalyzed Substitution Reactions 197Bernd Plietker

7.1 Introduction 1977.2 Iron-catalyzed Nucleophilic Substitutions 1977.2.1 Nucleophilic Substitutions of Non-activated C–X Bonds 1977.2.1.1 Introduction 1977.2.1.2 Nucleophilic Substitutions Using Lewis Acidic Fe Catalysts 1987.2.1.3 Substitutions Catalyzed by Ferrate Complexes 1997.2.2 Nucleophilic Substitution of Allylic and Propargylic C–X Bonds 2027.2.2.1 Reactions Catalyzed by Lewis Acidic Fe Salts 2027.2.2.2 Nucleophilic Substitutions Involving Ferrates 2057.3 Conclusion 213

References 214

8 Addition and Conjugate Addition Reactions to CarbonylCompounds 217Jens Christoffers, Herbert Frey, and Anna Rosiak

8.1 Introduction 2178.2 Additions to Aldehydes and Ketones 2188.2.1 Oxygen Nucleophiles 2188.2.2 Carbon Nucleophiles 2198.3 Additions to Imines and Iminium Ions 2238.4 Additions to Carboxylic Acids and Their Derivatives 2248.4.1 Oxygen Nucleophiles 2248.4.2 Carbon Nucleophiles 2258.5 Conjugate Addition to a,b-Unsaturated Carbonyl

Compounds 2268.5.1 Carbon Nucleophiles 2268.5.1.1 Michael Reactions 2268.5.1.2 Vinylogous Michael Reactions 2308.5.1.3 Asymmetric Michael Reactions 2328.5.1.4 Michael Reactions in Ionic Liquids and Heterogeneous

Catalysis 2338.5.2 Nitrogen Nucleophiles 2358.6 Synthesis of Heterocycles 2368.6.1 Pyridine and Quinoline Derivatives 2368.6.2 Pyrimidine and Pyrazine Derivatives 2388.6.3 Benzo- and Dibenzopyrans 238

References 239

9 Iron-catalyzed Cycloadditions and Ring Expansion Reactions 245Gerhard Hilt and Judith Janikowski

9.1 Introduction 2459.2 Cycloisomerization and Alder–Ene Reaction 2459.3 [2þ1]-Cycloadditions 249

VIII Contents

9.3.1 Iron-catalyzed Aziridine Formation 2499.3.2 Iron-catalyzed Epoxide Formation 2519.3.3 Iron-catalyzed Cyclopropane Formation 2529.4 [2þ2]-Cycloaddition 2549.5 [4þ1]-Cycloadditions 2569.6 [4þ2]-Cycloadditions 2579.6.1 Diels–Alder Reactions with Normal Electron Demand 2579.6.2 Diels–Alder Reactions with Neutral Electron Demand 2599.6.3 Diels–Alder Reactions with Inverse Electron Demand 2609.7 Cyclotrimerization 2609.8 [3þ2]-Cycloadditions 2629.9 [3þ3]-Cycloadditions 2639.10 Ring Expansion Reactions 2639.11 Conclusion 266

References 266

Index 271

Contents IX

Preface

Sustainability has emerged as one of the keywords in discussions in the fields ofpolitics, society and science within the past 20 years. The need for the production ofhigh-quality products with minimum waste and energy demands is a key challengein todays environment. This is even more salient when the increase in the worldpopulation and the decrease in fossil fuel resources are considered. In the field ofchemistry, the concept of sustainability is clearly defined by the use of low-wastechemical transformations plus the use of catalysts in order to decrease the amount ofenergy needed for a process. Althoughmost catalytic reactions fulfill the criteria for asustainable transformation on the macroscopic scale, often the high price of cata-lysts, which are mostly transition metal based and their ligands paired with aninherent toxicity contradict these criteria on a microscopic scale.This contradiction has spurred interest in developing transformations that make

use of sustainable catalysis. Organocatalysis and biocatalysis both fulfill the criteria ofsustainable catalysis: The catalysts are cheap, readily accessible and non-toxic. In thefield of sustainable metal catalysis, iron-catalyzed transformations have evolved aspowerful tools for performing organic synthesis. This development is somewhatsurprising if one considers that the earliest iron catalysis dates back to the 1960s, apoint in time where late transition metal catalysis using palladium, ruthenium orrhodiumwas still in its infancy. For some reason, which tome is one of themysteriesin metal catalysis, iron complexes never attracted the same interest in catalysis astheir higher homologues in Group VIII metals, e.g. Ru, Os, Rh, Ir, Pd and Pt. Thisdevelopment is even more astonishing if one considers the rich organometallicchemistry of iron. It would appear that the current discussion about sustainability(energy resources, non-toxic reagents, catalysts and green solvents, etc.) has led toresurrection of iron catalysis in organic synthesis as a way to generate sustainablemetalcatalysis.Due this recent revival, there is the need for an authoritative review of this

important chemistry. It is the purpose of this book not only to introduce thechemistry community to the most recent achievements in the field of catalysis,but also to create a deeper understanding of the underlying fundamentals in theorganometallic chemistry of iron complexes.

XI

Consequently, the first chapter of this multi-authored book introduces the readerto the most general aspects of organoiron chemistry. The stability of complexes,together with prominent examples of stoichiometric iron-mediated organic trans-formations, are presented in a concise way, providing a first insight into andreferences to the leading review articles.Iron complexes also play a dominant role in biological systems. The second

chapter focuses on aspects connected with heme and non-heme iron catalysts inbiological and biomimetic transformations. Most biological and biomimetic cata-lysts are employed in oxidation chemistry. Hence the reader can compare thesesystems with artificial catalytic oxidations, e.g. Gif chemistry and allylic and het-eroatom oxidations, which are summarized in Chapter 3. Catalytic reductions in thepresence of iron complexes are the synthetic counterpart to the oxidations and arereviewed in Chapter 4. Chapters 5–7 deal with different aspects of substitutionscatalyzed by iron complexes. The cross-coupling of aryl or alkenyl halides withGrignard reagents in the presence of catalytic amounts of iron salts, which arereviewed in Chapter 5, has experienced almost explosive progress within the past10 years. The current state of research is discussed with special emphasis on factorsinfluencing the reactivity, e.g. solvent and temperature. Chapter 6 completes thearomatic substitution section by reviewing iron-catalyzed electrophilic substitutions.Chapter 7 focuses on nucleophilic substitutions either by using iron salts as Lewisacidic catalysts that facilitate the substitution of a leaving group by coordination or byemploying low-valent ferrates as nucleophiles. Iron salts play a dominant role incatalytic addition and conjugate additions to carbonyl groups and these aspects areconcisely presented in Chapter 8. The canon of iron-catalyzed transformation isrounded up by Chapter 9, which summarizes the current state of research incycloaddition and ring expansion reactions.I hope this book, Iron Catalysis in Organic Chemistry. Reactions and Applications,

will stimulate further developments in this field and be of value to chemists both inacademia and in industry.

Stuttgart, April 2008 Bernd Plietker

XII Preface

List of Contributors

XIII

Angelika BaroUniversität StuttgartInstitut für Organische ChemiePfaffenwaldring 5570569 StuttgartGermany

Ingmar BauerTechnische Universität DresdenFachbereich ChemieBergstrasse 6601069 DresdenGermany

Matthias BellerLeibniz-Institut für Katalyse e.V. an derUniversität RostockAlbert-Einstein-Strasse 29a18059 RostockGermany

Carsten BolmRWTH AachenInstitut für Organische ChemieLandoltweg 152056 AachenGermany

Martin BröringPhilipps-Universität MarburgFachbereich ChemieHans-Meerwein-Strasse35032 MarburgGermany

Jens ChristoffersCarl von Ossietzky UniversitätOldenburgInstitut für Reine und AngewandteChemieCarl-von-Ossietzky-Strasse 9–1126111 OldenburgGermany

Stephan EnthalerLeibniz-Institut für Katalyse eV undUniversität RostockAlbert-Einstein-Strasse 29a18059 RostockGermany

Herbert FreyCarl von Ossietzky UniversitätOldenburgInstitut für Reine und AngewandteChemieCarl-von-Ossietzky-Strasse 9–1126111 OldenburgGermany