Rhodium Catalysis

Table of Contents

1. Frontmatter

2. Rhodium-Catalyzed C–B Bond Formation

   Ana B. Cuenca, Elena Fernández

   Abstract

   This chapter focuses on Rh-activation of boron-based reagents and its assistance in efficient catalytic borylation reactions. The introduction is a critical reflection of the importance that hydroborane reagents have had in reactions such as Rh-catalyzed hydroboration for the last 30 years. The next section shows a brief history of the Rh–B bond formation from Rh complexes and diboron reagents. The most relevant advances in Rh-catalyzed diboration are summarized in the following section. In the fourth section, examples of Rh-catalyzed β-boration of α,β-unsaturated substrates are collected, completing the fifth section with a description and comments about the new trends on Rh-catalyzed C–H and C–X borylation. At the end of this chapter, the authors compile a summary and their perspective for the related field from a mechanistic point of view.

3. Rhodium Catalysts for C–S Bond Formation

   Andrea Di Giuseppe, Ricardo Castarlenas, Luis A. Oro

   Abstract

   Sulfur-containing molecules are commonly found in chemical biology, organic synthesis, and materials chemistry. The preparation of these compounds through traditional methods usually required harsh reaction conditions. The use of transition-metal-based catalysts has allowed the development of more efficient and sustainable synthetic processes. Rhodium-catalyzed C–S bond formation through the reaction between sulfur sources such as S₈, thiols, or disulfides with organic substrates such as alkynes, allenes, and aryl/alkyl halides is one of the most important methods in the synthesis of thioethers. Here, we summarize recent efforts in the reactions of cross coupling, C–H activation, metathesis, thiolation, carbothiolation, and hydrothiolation for the C–S bond formation catalyzed by rhodium complexes, particularly highlighting the synthetic and mechanistic aspects.

4. Tandem Rhodium Carbonylation Reactions

   Philippe Kalck, Martine Urrutigoïty

   Abstract

   This review presents the recent advances in the rhodium-catalyzed tandem carbonylation reactions involving in the main step the hydroformylation. Such reactions open huge opportunities in synthetic chemistry, since they offer a general efficient strategy to synthesize building blocks for fine chemistry, starting from abundant and low price substrates and avoiding the formation of substantial amounts of by-products. This atom-efficient tandem reaction approach shows that rhodium has a privileged place in the CO chemistry, not only to perform the hydroformylation reaction but also to functionalize the aldehyde function in a one-pot process.

5. Asymmetric Hydroformylation Using Rhodium

   Anton Cunillera, Cyril Godard, Aurora Ruiz

   Abstract

   Asymmetric hydroformylation is a powerful catalytic reaction that produces chiral aldehydes from inexpensive feedstock (alkenes, syngas) in a single step. The elucidation of the different steps of the catalytic cycle and the characterization of the resting state, together with the discovery of several types of ligands, have made possible that nowadays a variety of chiral products incorporating a formyl unit can be enantioselectively prepared by Rh-catalyzed asymmetric hydroformylation, and that this process is now considered as a useful tool in organic synthesis.

6. Rhodium Catalyzed Decarbonylation

   Eduardo J. García-Suárez, Klara Kahr, Anders Riisager

   Abstract

   Rhodium catalyzed decarbonylation has developed significantly over the last 50 years and resulted in a wide range of reported catalyst systems and reaction protocols. Besides experimental data, literature also includes mechanistic studies incorporating Hammett methods, analysis of kinetic isotope effects as well as computational studies of model systems, which give an indication of the scope of the process. In this chapter, fundamental applications of Rh-catalyzed decarbonylation reactions are surveyed and discussed, including cross-coupling reactions, tandem reactions, and alternative methodologies for process intensification.

7. Recent Developments in Rhodium-Catalyzed Cyclocarbonylation Reactions

   Andrew J. Burnie, P. Andrew Evans

   Abstract

   Rhodium-catalyzed cyclocarbonylation reactions, which include the Pauson–Khand-type or [2+2+1] reactions, represent a powerful strategy for the synthesis of cyclic ketones through the combination of relatively simple unsaturated groups; namely, alkenes, alkynes, allenes, dienes, heterocumulenes, nitriles, and strained rings with carbon monoxide derived from either CO gas or through the decarbonylation of aldehydes. This chapter examines a variety of methods for the synthesis of carbo- and heterocyclic rings of different sizes, including diastereoselective and enantioselective approaches, and will also present the application of these reactions in the total synthesis of important natural products, as exemplified by (+)-asteriscanolide and (−)-ingenol.

8. Rhodium-Catalysed Hydrogenations Using Monodentate Ligands

   Mattia Cettolin, Pim Puylaert, Johannes G. de Vries

   Abstract

   The use of monodentate phosphorus ligands, such as phosphonites, phosphites and phosphoramidites, in the rhodium-catalysed asymmetric hydrogenation of a range of mostly alkene type substrates was reported for the first time in 2000. Not only are these ligands cheap and easy to prepare in one or two steps, their use has also created new opportunities, such as their robotic parallel synthesis and the use of complexes containing two different monodentate ligands, which tremendously increases the available diversity. This review covers the period between 2006 and 2016. Many new ligands have been made during this time; not only new variants on the three ligand types that were earlier reported, but also monodentate phosphines and secondary phosphine oxides. These were mostly tested on the usual N-acetyl-dehydroamino acids, itaconic esters and enamide type substrates. Other more novel substrates were N-formyl-dehydroamino acids, all the variants of the beta-dehydroamino acid family, enol esters, 2-methylidene-1,2,3,4-tetrahydro-β-carbolines, alkenes containing phosphonate or thioether substituents, several substituted acrylic acids as well as substituted cinnamic acids. The mechanism of the rhodium-catalysed hydrogenation with phosphites, phosphonites, phosphoramidites as well as phosphepines has been reported. A common theme in these mechanisms is the formation of a dimeric bimetallic complex after subjecting the [RhL₂(cod)]X or [RhL₂(nbd)]X (X = BF₄,PF₆, SbF₆) complexes to hydrogen. Since these hydrogenations are usually carried out in non-polar solvents, the formation of the expected RhL₂(Solvent)₂ complexes does not occur after the removal of the diene and instead each rhodium atom in these dimeric complexes coordinates not only to two monodentate ligands, but also in η⁶ fashion to an aromatic ring of one of the ligands that is bound to the other rhodium atom. These complexes can react with the substrate to form the substrate complex that is hydrogenated. Other studies also found that it is possible to form rhodium hydride complexes first, which react with the substrate to form product. There is one well-described industrial application on large scale in which a substituted 2-isopropyl-cinnamic acid is hydrogenated using a rhodium complex with a mixture of 2 eq. of 3,3’-dimethyl-PipPhos and 1 eq. of triphenylphosphine. The addition of the non-chiral triarylphosphine not only accelerated the reaction 50-fold, also the enantioselectivity was much improved. The product was used as a building block for Aliskiren^TM, a blood-pressure lowering agent.

9. CO2 Reduction Reactions by Rhodium-Based Catalysts

   Danilo Bonincontro, Elsje Alessandra Quadrelli

   Abstract

   Reduction reactions of CO₂ using chemicals obtained from renewable energy sources (as for example, dihydrogen obtained using renewable-issued electricity) or using directly renewable energy sources can contribute to store and use renewable energies in our current infrastructures. Rh-based catalysts have been playing a key role in the field of CO₂ reduction. From its very first application as homogeneous catalyst to now, several Rh-based catalytic systems have been successfully tested. This chapter gives the reader an overview as well as a mechanistic insight where possible into the Rh-catalysed CO₂ reduction reductions: production of formic acid and higher carboxylic acids with homogeneous catalysts, methane, CO and various oxygenated compounds via heterogeneous catalysis, and various products by means of electro- and photocatalysis.

10. Backmatter