This chapter outlines the acetyl chemicals family which includes acetic acid, acetaldehyde, methyl acetate, acetic anhydride, and vinyl acetate. It traces the manufacture of acetic acid and its use in a wide range of end-products, such as vinyl acetate, acetate esters, as a solvent specifically for the oxidation of p-xylene to terephthalic acid, and in food and pharmaceutical applications. It also talks about processes used for the production of acetic acid and the acetyl chemicals which involve homogeneous catalysis by transition metal ions or complexes. The chapter describes the reaction of acetaldehyde with acetic anhydride. This affords ethylidene diacetate, which can be thermally de-acetylated to form vinyl acetate with the elimination of acetic acid. The chapter finally refers to alkane oxidation, which is a radical chain process and main propagation that does not need to involve the metal ion.
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Chapter
Acetic acid and acetyl chemicals
Chapter
Alkene complexes
This chapter discusses alkene complexes. Alkene (olefin) complexes now exist of every transition metal and constitute one of the most important classes of coordination compounds. The development of the organometallic chemistry of olefins is closely connected with the rise of the petrochemical industry during the course of this century; olefins, in particular ethylene, are abundantly available from petrochemical feedstocks. The chapter then details the synthesis of alkene complexes and bonding of alkenes to transition metals. Olefins bind to transition metals via their π orbitals, by donating electron density into an empty metal d-orbital. However, since olefins are weak bases, the bond has to be stabilized by another bonding contribution: the donation of electron density from the metal to the olefin. Finally, the chapter explains the reactivity of alkene complexes.
Chapter
Alkylidene and alkylidyne complexes
This chapter studies alkylidene and alkylidyne complexes. Whereas metal alkyl complexes have a long history, the first examples of compounds with metal–carbon double bonds were not discovered until 1964 by E. O. Fischer. These compounds have become known as carbene complexes. The metal is in a low oxidation state, and the bonding of the carbene ligand is reminiscent to that of carbon monoxide (CO). A second group of M=C compounds, with a highly oxidized metal centre, was subsequently discovered by R. R. Schrock and these are called alkylidene complexes. The chapter then considers complexes with metal–carbon triple bonds, as well as the reactivity of alkylidene and alkylidyne complexes and it also looks at dinuclear alkylidene and alkylidyne complexes.
Chapter
Alkyne complexes
This chapter examines alkyne complexes. Alkynes (acetylenes) form complexes with transition metals in a similar way to alkenes, and similar bonding schemes can be applied. However, there are characteristic differences in the bonding of alkynes to metals compared to alkenes. Alkynes are stronger π-acceptors than alkenes; they have two orthogonal π-systems and can act as 2- as well as 4-electron donor ligands. Moreover, alkynes frequently undergo insertion reactions and are readily cyclotrimerized to give arenes. The chapter then studies the synthesis and bonding of alkyne complexes. Alkyne ligands can adopt a variety of coordination modes in mono and polynuclear complexes. The chapter also assesses the reactivity of alkynes. Alkynes, like alkenes, insert readily into metal–hydride bonds to give vinyl complexes.
Chapter
Allyl and dienyl complexes
This chapter focuses on allyl and dienyl complexes. The allyl ligand is the simplest in a series of non-cyclic conjugated anionic (enyl) ligands. Coordinated allyl is susceptible to nucleophilic attack—a property which has made allyl complexes invaluable in synthesis and is the basis of numerous catalytic reactions. The site of nucleophilic attack depends on the nature of the metal: allyl groups with cationic character are attacked in the 1,3-position, while anionic allyls react in the 2-position. The chapter then looks at the synthesis and reactivity of allyl complexes, before studying enyl complexes. Dienyl complexes, particularly iron tricarbonyl compounds, have important applications in stereoselective synthesis.
Book
Applied Organometallic Chemistry and Catalysis has two main objectives: to provide an overview of the influence of organometallic chemistry on homogeneous and heterogenous catalysis, and to provide an account of the principle commercial applications of homogeneous catalysis in industry. The first chapter provides some background to the subject, looking at the vital role that catalysis plays in the production of fuels and pharmaceuticals, amongst other things. The next chapter covers mechanistic organometallic chemistry. Chapter Three is related to hydroformylation and related reactions. The chapter that follows examines acetic acid and acetyl chemicals. The next two chapters look at nylon intermediates: buta- 1,3-diene hydrocyanation and olefin oligomerization and polymerization. The final chapter is about fine chemicals manufacture.
Chapter
Arene complexes
This chapter assesses arene complexes. Following the recognition in the early 1950s of the sandwich bonding principle for metallocenes, the existence of related sandwich complexes of neutral arenes such as benzene was demonstrated through the synthesis of bis-(benzene)chromium. The complex is isoelectronic to ferrocene and follows the 18-electron rule. Bonding in bis-(arene)metal complexes resembles that in metallocenes, and the MO diagram is qualitatively very similar. Since the aromatic ligands in bis-(arene) complexes are not negatively charged, there is no electrostatic contribution to bonding, and bis-(arene) complexes are in general less stable than metallocenes and more easily oxidized. The chapter then considers arene half-sandwich complexes; seven and eight membered ring ligands; heteroarene complexes; and multidecker complexes.
Chapter
Cyclopentadienyl complexes
This chapter evaluates cyclopentadienyl complexes. In 1948, Miller, Tebboth, and Tremaine, attempting to synthesize amines from olefins and nitrogen in the presence of iron catalysts, found that with cyclopentadiene, an iron-containing compound was formed. The new compound, bis-(cyclopentadienyl)iron, was named ‘ferrocene’ in the realization that it behaves much like a three dimensional arene. Soon afterwards, a whole series of bis-(cyclopentadienyl)metal complexes were prepared; by analogy these have become known as metallocenes. The chapter then looks at the synthesis of metallocenes and bonding in metallocene complexes, as well as the properties of metallocenes and bent sandwich complexes. It also considers cyclopentadienyl as a non-spectator ligand, studying ring slippage and fluxionality. Finally, the chapter explores mono-cyclopentadienyl (half-sandwich) complexes.
Chapter
A few basics
This chapter provides an overview of organometallic compounds, which are defined as substances containing direct metal–carbon bonds. The variety of the organic moiety in such compounds is practically infinite, ranging from alkyl substituents to alkenes, alkynes, carbonyls, and aromatic and heterocyclic compounds. Although some organometallic compounds have been known for a long time, it is only in the last four or five decades that organometallic chemistry has come into its own and experienced tremendous growth, both at a fundamental level where our insight into the nature of chemical bonds has been broadened by a variety of bonding situations without precedence elsewhere, and in its economic impact, such as catalysis. It is with the transition metals that the full diversity of organometallic chemistry becomes apparent. The chapter then explains the 18-electron rule, which provides a simple 'rule-of-thumb' basis for the discussion of structure and bonding.
Chapter
Fine chemicals manufacture
This chapter refers to the advantages to be derived from the use of homogeneous catalysts which concerns high selectivities. These advantages may be achieved in a wide range of chemical transformations. It reviews a mechanistic understanding of homogeneous catalysis which has developed to an increasingly sophisticated level. It also discusses the extent of the progress of successful applications of homogeneous catalysis in the manufacture of commodity chemicals and polymer intermediates for the production of fine chemicals. The chapter analyzes the application of organometallic chemistry and homogeneous catalysis, both of which can lead to economically viable alternative process routes that eliminate steps in the traditional and costly multi-stage procedures. The chapter reviews the ultimate application of high selectivities which concerns the development of catalysts for the synthesis of chiral compounds with high degrees of enantioselectivity.
Chapter
Homogeneous Catalysis with Organometallic Transition Metal Complexes
This chapter stresses that alkaline earth elements are more electronegative than the alkali metals and that their M–C bonds are more covalent. It emphasizes that alkaline earth compounds are Lewis acids and can coordinate two or more neutral ligands. This Lewis acidity is responsible for their high reactivity. The chapter then presents the bonding characteristics of Beryllium, as the alkaline earth element with the smallest radius. It shows the synthesis of magnesium and the formation of Grignard reagents. It also reviews how the metal–halogen exchange and C–H metallation. Next, it examines the structures of magnesium reagents and the reactions of magnesium reagents. The chapter then analyses the organometallic derivatives of the heavier alkaline earth metals — calcium, strontium, and barium.
Chapter
Hydroformylation and related reactions
This chapter focuses on hydroformylation, or the OXO (oxonation) reaction, which is used to describe the addition of CO and H2O to the C=C bond of an olefin or other unsaturated compounds. It talks about the synthesis of fatty alcohols from terminal olefins such as hept-l-ene. It also analyzes linear alcohols prepared by hydroformylation of mixtures of C12 olefins obtained by the controlled oligomerization of propylene, used in the synthesis of biodegradable detergents. The chapter deals with the bulk of productions via hydroformylation which involves relatively simple olefins. This is applied to a great variety of substituted olefins, both simple and complex. It illustrates several variations of olefin hydroformylation processes that have been commercialized.
Chapter
Introduction
This introductory chapter provides an overview of π-complexes, which are the complexes formed between metals and alkenes, alkynes, alkenyls, and arenes. This form of metal–carbon interaction is unique to transition metals. The moiety containing the π-bond may be neutral, such as ethene or ethyne, or formally anionic, as is the case with cyclopentadienyl or cyclo-octatetraenyl ligands. For transition metals, the 18-electron rule has a predictive function similar to the octet rule for main group elements. It provides a simple ‘rule-of-thumb’ basis for the discussion of structure and bonding, and although there are numerous exceptions, organometallic compounds which fulfil this rule tend to represent relative energy minima. In order to determine whether a compound obeys the 18-electron rule or not, it is useful to follow certain electron counting conventions. Ligands are classified according to the number of electrons they formally donate to the metal centre, following the covalent (electroneutral) counting convention.
Chapter
Introduction
This chapter provides a background on the reagents of the general structure RM, where R is an organic fragment and M is a metal that had a profound effect on organic synthesis. It explains the chemistry of the organometallic reagents of sodium, potassium, lithium, and magnesium by regarding the reagents as equivalent to a carbanion R- with a metal cation M+. It also discusses the use of carbanion R- for reacting with various organic electrophiles to make carbon-carbon bonds. The chapter covers various structural types and methods of preparation and uses in synthesis of the dual reactivity of the organometallic reagent. It cites examples on the most important uses of reagents, such as the alkoxide salt that is produced when the reaction mixture is poured into water during the work-up procedure.
Chapter
Mechanistic organometallic chemistry
This chapter recognizes the vital role played by organometallic chemistry in the understanding of industrial process applications and looks at developments in organometallic chemistry which occurred in parallel to industrial applications. It refers to the successful commercial application of homogeneous catalysis. This is based on a good understanding of the underlying organometallic chemistry. It also illustrates a framework of transformations upon which the construction of catalytic cycles can be based. The chapter discusses the rules of organometallic complexes and their reactions. This emphasizes that diamagnetic organometallic complexes of transition metals may exist in significant concentration at moderate temperatures. It describes organometallic reactions that proceed by a series of elementary steps involving intermediates with 16 or 18 valence electrons.
Chapter
Metal alkyl complexes
This chapter examines metal alkyl complexes. The making and breaking of metal–carbon σ-bonds plays an important role in organometallic chemistry and is central to its application to catalysis. Whenever alkanes, alkenes, or alkynes are generated, hydrogenated, polymerized, or functionalized, metal alkyl intermediates are involved. It is estimated that about three quarters of all products of the chemical industry pass through a catalytic process at some stage. Most metal alkyl complexes containing donor ligands also follow the 18-electron rule. However, there are numerous complexes which are thermally quite stable but cannot be explained on the basis of the 18-electron rule. These compounds are often electronically highly unsaturated and owe their existence to the kinetic stabilization afforded by sterically demanding ligands. The chapter then considers the reactivity of metal alkyls, and looks at transition metal alkyl complexes in vivo.
Chapter
Metal carbonyl complexes
This chapter discusses metal carbonyl complexes, one of the most important classes of organometallic compounds. Carbon monoxide (CO) binds firmly to blood haemoglobin and renders it unavailable for oxygen transport. Metal carbonyls, in particular the volatile compounds, are therefore highly toxic; nickel tetracarbonyl Ni(CO)4 is a very potent carcinogen. The structures of metal carbonyls can be explained using the 18-electron rule. This is fulfilled if Cr, Fe, and Ni bind six, five, and four CO ligands, respectively, to give monomeric compounds. The carbonyls of Mn and Co form metal–metal bonded dimers to attain an 18 VE configuration. The chapter then looks at metal carbonyl anions, metal carbonyl hydrides, metal carbonyl halides, and metal carbonyl clusters.
Chapter
Metallated alkenes
This chapter talks about direct and indirect methods that can be used for the preparation of metalated alkenes, including the alkenyl potassium reagent produced using the base potassium amide in liquid ammonia. It examines the equation that shows that allylic deprotonation is a competing reaction that becomes more important as the ring size increases. It also points out how sodium and potassium alkenes are not used in synthesis to anything like the same extent as the corresponding lithium compounds. The chapter describes reactions that are referred to as the lithium-halogen exchange, which is considered as a nucleophilic attack on the halogen atom that occurs with retention of the olefin configuration. The chapter explains that the alternative reaction is the conversion of tin compounds to lithium counterparts wherein the retention of the olefin configuration is observed.
Chapter
Metallated alkynes
This chapter talks about the high-s character of an sp hybridized carbon atom, which meant that an acetylene anion is stabilized, and the deprotonation of acetylenes, which is possible with a wide range of strong bases. It emphasizes the careful control of conditions of a strong base in the deprotonation of an acetylene to avoid side reactions, particularly on substituted acetylenes. It also describes the formation of danions as a major side reaction that occurs if the acetylene is momentarily exposed to an excess of base, the appropriate solvent is used, or the reaction temperature rises. The chapter explains the elimination of hydrogen halide with an amide base in liquid ammonia, which is a useful alternative to deprotonation as a synthesis of metalated alkynes. It clarifies how alkylation occurs with primary alkyl bromides and iodides under basic conditions involving liquid ammonia as solvent.
Chapter
Metallated aromatic compounds
This chapter discusses the generation of metalated aromatic compounds from aromatic halides, which is considered an efficient route for reagents. It mentions phenyl Grignard and phenyllithium prepared from bromobenzene and the metal in ether, including the regiospecific production of aryllithium compounds that occurs when aromatic halides react with butyllithium. It also examines bromide when it is converted into a lithium reagent. The chapter examines reactions of simple aryl Grignard and lithium compounds that are the same as their alkyl counterparts. The chapter covers topics that are essential to aromatic compounds. These are explained with illustrations of the reactions of the metalated species. It cites substituents that exert a profound effect on the reaction of a benzene ring with butyllithium in both deprotonation and lithium-halogen exchange reactions.
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