Iron Catalysis II

Table of Contents

1. Frontmatter

2. Iron Catalysis: Historic Overview and Current Trends

   Eike B. Bauer

   Abstract

   Iron catalysis is a growing area of research, as seen by an exponential increase in the publication activities on the topic. This introductory chapter provides a historic overview of the development of iron catalysis including some notable milestones. The advantages of iron, i.e., its abundance, low price, and relative nontoxicity, are discussed, and an overview of the main type of reactions catalyzed by iron is outlined. The advances of heterogeneous iron catalysis (which is not covered in this volume) are exemplified with a few notable cases. Finally, the potential impact of metal impurities in iron sources on the catalytic activity is discussed.

3. The Development of Iron Catalysts for Cross-Coupling Reactions

   Robin B. Bedford, Peter B. Brenner

   Abstract

   Cross-coupling between organometallic nucleophiles and organic electrophiles is currently one of the most widely investigated areas of organic homogeneous catalysis with iron. This overview charts the development and application of iron catalysts for cross-coupling reactions, focusing predominantly on findings over the last 5 years.

4. Iron-Catalyzed Cross-Dehydrogenative-Coupling Reactions

   Masumi Itazaki, Hiroshi Nakazawa

   Abstract

   Cross-dehydrogenative-coupling (CDC) reactions involving C–H bond activation are powerful tools for C–C bond formation and are highly significant from the perspective of atom economy. A variety of carbon–carbon bond-forming reactions utilizing various coupling partners are known today. Iron-catalyzed organic syntheses have attracted considerable attention because iron is an abundant, inexpensive, and environmentally benign metal. This chapter summarizes the development of iron-catalyzed CDC reactions, the reaction mechanism, and the role of the Fe species in the catalytic cycle in the period from 2007 to 2014.

5. Iron-Catalyzed Carbon–Nitrogen, Carbon–Phosphorus, and Carbon–Sulfur Bond Formation and Cyclization Reactions

   Jean-Luc Renaud, Sylvain Gaillard

   Abstract

   The formation of carbon–heteroatom bonds (C–X bonds with X=N, S, P) upon addition of X-nucleophiles or X-electrophiles to unsaturated alkynes and alkenes, cross-coupling reactions, cycloadditions, tandem or consecutive reactions, or C–H functionalization is an attractive strategy in organic synthesis and is an intensive research area. Many organometallic species, more specifically palladium, nickel, and rhodium complexes, have paved the way to useful synthetic applications in this field. This chapter will cover iron-catalyzed bond-forming reactions between carbon and a heteroatom.

6. High-Valent Iron in Biomimetic Alkane Oxidation Catalysis

   Michaela Grau, George J. P. Britovsek

   Abstract

   The combination of iron salts or complexes with strong oxidants such as hydrogen peroxide results in the formation of high-valent iron oxo species, the nature of which has been under discussion in the chemical literature for more than a century. Recent advances in the design and development of molecular iron-based oxidation catalysts and their mechanistic understanding are summarised in this chapter, in particular iron complexes featuring tetradentate and pentadentate ligands. Inspired by enzymatic systems based on heme and nonheme ligand environments, the development of biomimetic iron-based catalysts for the selective oxidation of alkanes and alkenes can potentially be applied in a range of areas, from late stage functionalisation of natural product synthesis to large-scale oxidation of hydrocarbons.

7. Iron-Catalyzed Reduction and Hydroelementation Reactions

   Christophe Darcel, Jean-Baptiste Sortais

   Abstract

   During the last two decades, iron has proved to be an interesting transition metal which is a highly valuable alternative to classical precious ones for catalyzing organic transformations including the reduction of unsaturated C–C or C–heteroatom bonds. This chapter summarizes the rapid development of iron catalyzed selective reductions of alkene, alkyne, carbonyl and carboxylic derivatives. The emerging topic of hydroboration of alkenes and alkynes is also described.

8. Iron-Catalyzed Oligomerization and Polymerization Reactions

   Benjamin Burcher, Pierre-Alain R. Breuil, Lionel Magna, Hélène Olivier-Bourbigou

   Abstract

   Having the tremendous industrial importance of thermoplastics and elastomers in mind, it is not surprising to see a proliferation of studies on a variety of catalytic systems for polymerization and oligomerization of unsaturated hydrocarbons. Over the last 15 years, the development of mid- to late transition metal catalysts has provided significant advances in this area. The availability of iron combined with its low environmental impact and its tolerance to heteroatom functions attracts significant interest from both academia and industry. In the late 1990s, key milestones have been the development of well-characterized bulky bis(imino)pyridine-Fe(II) precatalysts, mainly for the polymerization or oligomerization of ethylene. This chapter provides a brief overview of the key developments reported in the last 5 years in the literature in the field of iron-catalyzed olefin and diolefin polymerization and oligomerization. Emphasis has been placed on ethylene oligomerization and polymerization, with a particular interest in ligand architecture modifications. The advances in characterization and understanding of catalytically active iron species and the corresponding mechanisms are reported. Heterogenization of bis(imino)pyridine iron catalytic systems has been considered for ethylene transformation and will also be covered in this chapter. The interest of iron catalysts for multiple single-site approaches such as reactor blending and tandem catalysis is also described. Finally, iron catalyst systems also present interesting features for diene polymerization even though both activities and selectivities remain far from those observed for conventional catalysts.

9. Enantioselective Iron Catalysts

   Thierry Ollevier, Hoda Keipour

   Abstract

   Synthetic organic transformations catalyzed by iron complexes have attracted considerable attention because of an enviable list of assets: iron is an ubiquitous, inexpensive, and environmentally benign metal. It has been documented that various chiral iron complexes can be used in many reactions such as oxidation, cyclopropanation, hydrogenation, hydrosilylation, and alkane hydroxylation. This chapter summarizes recent developments, mainly from 2004 to 2014, of enantioselective iron catalysts.

10. Molecular Iron-Based Oxidants and Their Stoichiometric Reactions

    David P. de Sousa, Christine J. McKenzie

    Abstract

    Molecular iron-based oxidants can oxidize organic substrates under relatively mild conditions, sometimes even in water. If these reactions can be converted to catalytic protocols, they hold great promise for the development of greener methods for this particularly messy class of reaction. For application in organic synthesis, the biggest question is: How selective can the reactions be? The supporting ligands in these compounds are crucial for tuning the electronic structure of a catalytically competent iron-based oxidant and its selectivity in terms of the production of a single, even enantiopure, product. A thorough understanding of the stoichiometric generation of molecular iron-based oxidants and their subsequent reactivity is an important step for the development of new iron-based catalysts. Ideally, and in analogy to many of nature’s iron-based enzymes, their regeneration under catalytic conditions could involve the activation of dioxygen from air. This chapter will focus on the stoichiometric reactions of iron compounds with potential oxidizing agents including O₂, peroxides, oxygen-atom donor reagents, and even water, to form iron-based oxidizing species and the reactions of these usually very transient species with oxidizable substrates. This chapter might be especially inspiring for researchers in the field of iron catalyst design.

11. Backmatter