Palladacycles

Catalysis and Beyond

Anant Kapdi, Debabrata Maiti

• Publisher: Elsevier
• Year: 2019
• Print ISBN: 9780128155059
• eBook ISBN: 9780128165164
• Topic: Physical Sciences
• Subtopic: Inorganic Chemistry

Palladacycles: Catalysis and Beyond provides an overview of recent research in palladacycles in catalysis for cross-coupling and similar reactions. In the quest for developing highly efficient and robust palladium-based catalysts for C-C bond formation via cross-coupling reactions, palladacycles have played a significant role. In recent years, they have found a wide variety of applications, ranging from catalysts for cross-coupling and related reactions, to their more recent application as anticancer agents. This book explores early examples of the use of palladacyclic complexes in catalysis employing azobenzene and hydrazobenzene as coordinating ligands. Its applications in processes such as selective reduction of alkenes, alkynes, or nitroalkanes are also covered. Palladacycles: Catalysis and Beyond reveals the tremendous advances that have taken place in the potential applications of palladacycles as versatile catalysts in academia and industry. It is a valuable resource for synthetic chemists, organometallic chemists, and chemical biologists. - Reviews the importance and various applications of palladacycles in academic research and industry, including industrial scale applications - Includes the impact of palladacycles on coupling reactions and potential applications as anticancer agents - Features coverage of nano and colloidal catalysis via palladacyclic degradation

Chapter 1

Palladacycles as Efficient Precatalysts for Suzuki-Miyaura Cross-Coupling Reactions

José M. Vila; M. Teresa Pereira; Fátima Lucio-Martínez; Francisco Reigosa Departamento de Química Inorgánica, Universidad de Santiago de Compostela, Santiago de Compostela, Spain

Abstract

Palladacycles are a paramount class of organometallic compounds which, over recent years, have arisen as valuable devices in the preparation of organometallic substances, especially in cross-coupling processes leading to the formation of carbon-carbon bonds, namely the Suzuki-Miyaura reaction. Palladacycles constitute the precatalysts that provide the necessary palladium itself in an oxidation state dependant on the proposed catalytic cycle, i.e., Pd(0)/Pd(II)//Pd(II)/Pd(IV), or alternatively, where palladium intercedes in the course of the reaction, more often than not palladacycles emerge as intermediates. Well known reasons for their ample use in such performances are, among others, that they are fairly stable and that with few exceptions may be readily prepared in reasonably good yields. After the pioneering work by Herman et al. involving phosphine palladacycles, countless amounts of new palladacycles have been tested for this purpose

Keywords

Palladacycles; Ferrocene; Organometallic; Catalyst; Oxime; Pincer; Imines

Contents

• 1. Introduction
• 2. Imine and Amine Palladacycles
• 3. Oxime Palladacycles
• 4. Ferrocene Palladacycles
• 5. Pincer Palladacycles
• 6. Phosphorus Donor Atom Palladacycles
• 7. Carbene Palladacycles
• 8. Alternative Palladacycles
• 9. Conclusions
• References

1 Introduction

Palladacycles (1–5) are a paramount class of organometallic compounds which, over recent years, have arisen as valuable devices in the preparation of organometallic substances, especially in cross-coupling processes leading to the formation of carbon-carbon bonds, namely the Suzuki-Miyaura reaction (6–10). Palladacycles constitute the precatalysts that provide the necessary palladium itself in an oxidation state dependant on the proposed catalytic cycle, i.e., Pd(0)/Pd(II)//Pd(II)/Pd(IV), or alternatively, where palladium intercedes in the course of the reaction, more often than not palladacycles emerge as intermediates. Well known reasons for their ample use in such performances are, among others, that they are fairly stable and that with few exceptions may be readily prepared in reasonably good yields. After the pioneering work by Herman et al. (11–13) involving phosphine palladacycles, countless amounts of new palladacycles have been tested for this purpose.

The Suzuki-Miyaura process consists in the cross-coupling reaction of organoborated compounds (Ar₁-B(OR)₂) with electrophiles (Ar₂-X) catalyzed by palladium (14, 15). This is one of the most efficient methods for making carbon–carbon bonds between aryl rings (Scheme 1.1).

Scheme 1.1 The Suzuki-Miyaura cross-coupling reaction.

Precisely, one of the main advantages of the Suzuki-Miyaura reaction is that it uses organoborated species as precursors; in particular, various reactions have been carried out with organoborated derivatives, such as esters of boronic acids and alkylboranes. Another important aspect is the possibility of using water as solvent (16, 17). Because water is an excellent solvent for microwave heating, the combined use of water as solvent plus heating by microwave radiation has also been considered (18). It is generally accepted that the catalytic cycle for the Suzuki–Miyaura reaction is initiated with an oxidative addition of the electrophile (Ar₂-X) to the catalyst generating the intermediate {Ar₂-[Pd]-X}. The resulting complex undergoes transmetallation between {Ar₂-[Pd]-X} and (Ar₁-B(OH)₂) to give the disubstituted palladium species {Ar₁-[Pd]-Ar₂}, after which reductive elimination of the palladium-disubstituted moiety occurs, releasing the coupling product (Ar₁-Ar₂) and regenerating the catalyst, which is incorporated again into the cycle; the latter step verifies the catalytic efficiency of the palladacycle (Scheme 1.2).

Scheme 1.2 The Suzuki-Miyaura catalytic cycle.

The amount of references, inclusive of reviews, related to palladacycles that have been used in the aforementioned process is overwhelming. So, far from being comprehensive on this issue, the reader may find an account of the most outstanding aspects of this chemistry as from the work of Dupont (3) and Bedford (Chapter 8...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Chapter 1: Palladacycles as Efficient Precatalysts for Suzuki-Miyaura Cross-Coupling Reactions
• Chapter 2: Palladacycles as Precatalysts for Heck and Sonogashira Cross-Coupling Reactions
• Chapter 3: Palladacycles as Efficient Precatalysts for Negishi and Buchwald-Hartwig Amination Reactions
• Chapter 4: Introduction of Water-Solubility in Palladacycles and Their Catalytic Applications
• Chapter 5: Palladacyclic Complexes as Efficient Catalysts for CH Bond Functionalization Reactions
• Chapter 6: Multicomponent Reaction Sequences Using Palladacyclic Complexes
• Chapter 7: Enantioselective Synthesis Using Chiral Palladacycles
• Chapter 8: Nanoparticular or Colloidal Pathways for Palladacycles-Mediated Catalytic Processes
• Chapter 9: Palladacycles as Potential Anticancer Agents
• Chapter 10: Miscellaneous Applications of Palladacycles
• Index