Catalytic processes hydroformylation

Much of the recent interest in insertion reactions undeniably stems from the emphasis placed on development of homogeneous catalysis as a rational discipline. One or more insertion is involved in such catalytic processes as the hydroformylation (31) or the polymerization of olefins 26, 75) and isocyanides 244). In addition, many insertion reactions have been successfully employed in organic and organometallic synthesis. The research in this general area has helped systematize a large body of previously unrelated facts and opened new areas of chemistry for investigation. Heck 114) and Lappert and Prokai 161) provide a comprehensive compilation and a systematic discussion of a wide variety of insertion reactions in two relatively recent (1965 and 1967) reviews. 

Rhodium complexes of phosphorus based ligands are of considerable importance as (pre-)catalysts in hydroformylation which has developed into one of the most important homogeneous catalytic processes [57]. A recent advantage in this field involved the use of phosphinines as ligands whose low-lying r -orbitals provide for similar r-acceptor qualities as for phosphites [13, 58]. 

Tulchinsky and Miller (32) patented dendritic macromolecules, their metal complexes, and their use in catalytic processes such as hydroformylation. Dendrimers containing organophosphites, organophosphonites, and/or organophosphinites were... 

A number of publications have appeared revealing that catalytic processes which are unsuccessful with vinylic fluondes can be applied effectively to fluoro-alkyl- and fluoioarylethylenes Hydroformylation [56] and related reactions such as amidocarbonylation [571 will proceed in high yield and regioselectivity The choice of the catalyst system, especially of rhodium and cobalt catalysts, allows either regioselective reaction to proceed A few of the large number of syntheuc variants are given in equation 45... 

Another important reaction typically proceeding in transition metal complexes is the insertion reaction. Carbon monoxide readily undergoes this process. Therefore, the insertion reaction is extremely important in organoiron chemistry for carbonylation of alkyl groups to aldehydes, ketones (compare Scheme 1.2) or carboxylic acid derivatives. Industrially important catalytic processes based on insertion reactions are hydroformylation and alkene polymerization. 

It was shown15) by asymmetric hydroformylation of linear butenes that asymmetric induction in hydroformylation occurs substantially before or during metal alkyl intermediate formation, which, according to the accepted hydroformylation mechanism 2I-57,58), is the second step in the catalytic process (see also Sect. 5.1). 

Hydroformylation is a multistep catalytic process from the data on the cobalt-catalyzed reaction it has generally been proposed that the reaction occurs according to the scheme in Fig. 12 21). 

One of the most interesting catalytic reactions to be discovered is the so-called oxo reaction. The oxo reaction consists of the catalytic addition of carbon monoxide and hydrogen to olefins to form, primarily, aldehydes possessing one carbon atom more than the original olefin. This hy-droformylation reaction was developed during World War II by Roelen and co-workers (22) in Germany. While they utilized solid Fischer-Tropsch cobalt-thoria catalyst, it became apparent to them that the hydroformylation reaction was probably a homogeneous catalytic process with either dicobalt octaearbonyl or cobalt hydrocarbonyl as the catalyst. 

An example is the rhodium catalyzed hydroformylation reaction, which is an industrially important homogenous catalytic process [3]. In contrast, it is amazing that such an important transition-metal catalyzed C/C bond-forming process has been employed only rarely in organic synthesis [4]. Part of the reason stems from the difficulty in controlling stereoselectivity. Even though some recently developed chiral rhodium catalysts allow for enantio- and diastereoselective hydroformylation of certain specific classes of alkenes [5, 6], only little is known about the diastereoselective hydroformylation of acyclic olefins [7, 8]. 

The hydroformylation of olefins is one of the largest and most prominent industrial catalytic processes, producing millions of tons of aldehydes annually [102]. Initially, cobalt-carbonyl species were used as catalyst, though rhodium complexes modified by special ligands, usually phosphines, are predominantly used nowadays. Over the last two decades, continued development of new phosphine and phosphite ligands has allowed significant advances in hydroformylation chemistry, especially with respect to catalyst selectivity and stability [103]. 

Other approaches that have been suggested include catalytic asymmetric hydroformylation of 2-methoxy-6-vinylnaphthalene (6) using a rhodium catalyst on BINAPHOS ligand followed by oxidation of the resultant aldehyde 7 to yield 5-naproxen (Scheme 6.3).22 However, the tendency of the aldehyde to racemize and the co-generation of the linear aldehyde isomer make the process less attractive. Other modifications related to this process include catalytic asymmetric hydroesterification,23 hydrocarboxylation,24 and hydrocyanation.25... 

The 7t ligands play important roles in a large number of homogeneous catalytic processes. Alkene polymerization and a variety of other reactions involve alkene coordination (see Chapters 6 and 7). As the name suggests, CO is the main ligand in carbonylation reactions (see Chapter 4). All four ligands CO, alkene, H , and PR3, play important parts in hydroformylation reactions (see Chapter 5). 

Three commercial homogeneous catalytic processes for the hydroformyla-tion reaction deserve a comparative study. Two of these involve the use of cobalt complexes as catalysts. In the old process a cobalt salt was used. In the modihed current version, a cobalt salt plus a tertiary phosphine are used as the catalyst precursors. The third process uses a rhodium salt with a tertiary phosphine as the catalyst precursor. Ruhrchemie/Rhone-Poulenc, Mitsubishi-Kasei, Union Carbide, and Celanese use the rhodium-based hydroformylation process. The phosphine-modihed cobalt-based system was developed by Shell specih-cally for linear alcohol synthesis (see Section 7.4.1). The old unmodihed cobalt process is of interest mainly for comparison. Some of the process parameters are compared in Table 5.1. 

Anchoring of active catalysts to insoluble materials such as oxides, silicates, and zeolites often reduces the loss of catalyst during the catalytic process (66). The fixation of the active centers can be achieved either by means of their interaction with hydroxyl groups on a solid surface or, alternatively, by means of interactions between the CO ligands of the metal complex and a Lewis acidic center of the surface. Zeolite-supported cobalt catalysts have been reported for hydroformylation reactions (67). 

A central metal ion usually has a pronounced effect on the reactivity of a coordinated ligand at the coordinated atom or atoms. An important reaction of this type which has synthetic value is the reaction of alkenes and alkynes with hydrogen and carbon monoxide in the presence of a metal carbonyl. This is actually the catalytic process of hydroformylation and, although catalysis is beyond the scope of this work, it is nevertheless of interest from the standpoint of ligand reactivity. The reaction of ethylene with hydrogen and carbon monoxide in the presence of HCo(CO)4 as a catalyst is proposed to proceed (at least formally) through the steps shown 1U13) ... 

The hydroformylation of olefins is the most widely used homogeneous catalytic process using CO gas. It involves the addition of one molecule of CO and H2 to an olefin in the presence of a transition metal catalyst, most frequently based on cobalt or rhodium, resulting in the formation of an aldehyde. Generally, it is believed that the activation of H2 in cobalt-catalysed hydroformylation occurs on the unsaturated species Co2(CO)7 or Co(acylXCO)3 formed by the following reactions ... 

Edward Frankland (1825-1899) discovered the first transition metal alkyl complexes - diethylzinc ( mobile fluid") and ethyl-zinc iodide ( white mass of crystals ) - while he worked in Robert Bunsen s Marburg laboratory (1849). Frankland was later a professor of chemistry in London. Alkyl-metal bonding occurs in practically all catalytic processes involving hydrocarbons, e. g., hydroformylation (Section 2.1.1), hydrogenation of olefins (Section 2.2), hydrocarbon activation (Section 3.3.6), and C-H-activation (Chapter 4). 

Whatever metal is used, homogeneous processes suffer from high cost resulting from the consumption of the catalyst, whether recycled or not. This is why two-phase catalytic processes have been developed such as hydroformylation catalyzed by rhodium complexes, which are dissolved in water thanks to hydrophilic phosphines (cf. Section 3.1.1.1) [17]. Due to the sensitivity of most dimerization catalysts to proton-active or coordinating solvents, the use of non-aqueous ionic liquids (NAILs) as catalyst solvents has been proposed. These media are typically mixtures of quaternary ammonium or phosphonium salts, such as 1,3-dialkylimi-dazolium chloride, with aluminum trichloride (cf. Section 3.1.1.2.2). They prove to be superb solvents for cationic active species such as the cationic nickel complexes which are the active species of olefin dimerization [18, 19]. The dimers. 

A remarkable example of the cooperation of different active sites in a polyfunctional catalyst is the one-step synthesis of 2-ethylhexanol, including a combined hydroformylation, aldol condensation, and hydrogenation process [17]. The catalyst in this case is a carbonyl-phosphine-rhodium complex immobilized on to polystyrene carrying amino groups close to the metal center. Another multistep catalytic process is the cyclooligomerization of butadiene combined with a subsequent hydroformylation or hydrogenation step [24, 25] using a styrene polymer on to which a rhodium-phosphine and a nickel-phosphine complex are anchored (cf Section 3.1.5). 

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