Telomerizations and Oligomerizations

Telomerization and oligomerization reactions of unsaturated substrates are certainly one of the most useful application of transition metal catalysis (together with Ziegler—Natta polymerizations). This problem is considered in other chapters of the present book we shall therefore present only a few typical examples of applications. 

An important difference between Pd and Ni catalysis is that Pd affords linear dimerization products whereas Ni catalysts are more suitable when cyclic dimers or trimers are required. However, linear oligomers can also be obtained with Ni catalysts. 

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Direct fluorination with elemental fluorine is not practical for commercial synthesis of fluorinated surfactants. Elemental fluorine is extremely reactive and difficult to handle. The heat of formation of the C—bond (about 460 kJ/mol or 110 kcal/mol) and the H—F bond (566 kJ/mol or 135 kcal/mol) exceeds that of the C—C bond (about 348 kJ/mol or 83 kcal/mol) [1]. Hence, the fluorination with elemental fluorine leads to a violent fragmentation of the substrate unless the reaction is carefully controlled and the reaction heat effectively dissipated [2,3]. Commercially important pathways to fluorinated surfactants are electrochemical fluorination, telomerization, and oligomerization of tetrafluoroethylene [4-6]. 

Prepa.ra.tlon There are five methods for the preparation of long-chain perfluorinated carboxyUc acids and derivatives electrochemical fluorination, direct fluorination, telomerization of tetrafluoroethylene, oligomerization of hexafluoropropylene oxide, and photooxidation of tetrafluoroethylene and hexafluoropropylene. 

Linear oligomerization and telomerization of butadiene take place with nickel complexes in the presence of a proton source (7). In addition, cooligomerization of butadiene with functionalized olefins such as methacrylate is catalyzed by nickel complexes [Eq. (4)] (12, 13) ... 

Solutions of the nickel(O) and palladium(O) complexes of 1,3,5-triaza-7-phosphaadamantane, PTA (82) and tris(hydroxymethyl)phosphine (98) in water catalyze the oligomerization and telomerization of 1,3-butadiene at 80 °C. Although high yields and good selectivities to octadienyl products (87 %) were obtained, the complexes (or the intermediate species formed in the reaction) dissolve sufficiently in the organic phase ofthe monomer and the products to cause substantial metal leaching [17],... 

Schuchardt U, Dos Santos EN, Santos Dias F (1989) Butadiene oligomerization and telomerization catalyzed by transition metal complexes supported on organic polymers. J Mol Catal 55 340-352... 

Butadiene as raw material is available in high amounts from the C4 fraction of raffmation processes. The telomerization of butadiene itself catalyzed by different metal catalysts is a well documented reaction. Depending on the catalyst and on the conditions different telomeres may be synthesized. Carrying out the reaction under carbon dioxide instead of argon atmosphere, 1,3,7-octatriene becomes the main product Pioneering work of Inoue and co-workers in 1976 showed that the same reaction under carbon dioxide atmosphere lead to co-oligomeres 2, 5 and 6 when palladium complexes are used as catalysts (Scheme 1). 

Promising results have been reported by various laboratories since 1990 on catalysis in molten salts, notably for catalytic hydrogenation, hydroformylation, oxidation, alkoxycarbonylation, hydrodimerization/telomerization, oligomerization, and Trost-Tsuji coupling [113]. A continuous-flow application to the linear dimerization of 1-butene on an ionic-liquid nickel catalyst system reached activities with TON > 18000 [116]. 

Some of the examples presented in Section 4.2.2 are, however, not only restricted to the two liquid phases discussed, but contain in addition a further gas phase [89]. For instance, in hydroformylation a water-gas phase exists, in oligomerizations an ethylene phase and in telomerizations a butadiene phase. For these gas-liquid-liquid systems there is so far only a limited amount of published information on the reaction engineering aspects [90]. One exception is the study of 1-oc-tene hydrogenation using a rhodium/TPPTS catalyst [91], in which both thermodynamics and kinetics have been investigated in some detail. The same group also studied the hydroformylation of 1-octene [92]. 

In particular, the concepts of biphasic catalysis were used in telomerization (Section 6.9), oligomerization (Section 6.12), hydrogenation (Section 6.2), and hydro-formylation (Section 6.1) reactions. Therefore these reactions will be considered in the following sections in some more detail and thus complement the appropriate Chapters as far as technical concepts are concerned. 

Oligomerizations, polymerizations and telomerizations are covered in other parts of this section, since C-C/C-C bond forming additions (dicarborations) are involved. Metal-mediated hydroalkylations of olefins with CH acidic compounds and hydroarylations with formal addition of aromatic C—H bonds to olefins are also known2, however, only a few examples of stereoselective applications have been reported (Section 1.5.8.2.6.). 

Telomerization is defined as an oligomerization of dienes accompanied by addition of a heteroatom or carbon nucleophilic reagent10. It is catalyzed by various organometallic compounds of transition metals, especially palladium compounds. The nucleophiles, such as water, alcohols, amines or carboxylic acids, as well as enamines, nitroalkanes and stabilized carban-ions, are mainly introduced in the terminal position of the dimeric molecule in excellent yield10. It is also possible to direct the reaction towards an internal product functionalization. Telo-merizations with heteronucleophiles are regarded as heterocarborative addition reactions and are described in Section 1.5.8.4. 

Review W. Reim, A. Behr, M. Roper, Alkene and alkyne oligomerization, cyclooligomerization and telomerization reactions, in Comprehensive Organometallic Chemistry, (Eds. G. Wilkinson, F. G. A. Stone, E. W. Abel), I rgamon, Oxford, 1984. 

Two distinct but related strategies that rely on templates to control the number of monomers incorporated into an oligomeric product can be envisioned. One of these approaches, shown in Scheme 8-2, relies on templated radical macrocyclization reactions to control telomer size [14, 15]. This strategy requires attachment of all of the monomer units to the template backbone and uses macrocyclization, which faces competition from intermolecular chain transfer, to control the telomer length. The chain transfer agent T-I (i.e., telomerization terminator) is not attached to the template. 

These unusual properties were the basis of the fluorous biphasic catalysis process (FBC) first published in 1994 by Horvdth and Rdbai and demonstrated using hydroformylation chemistry as a pertinent example (7, 2) in a 1991 Ph.D. thesis, that was unfortunately not readily available to the homogeneous catalysis community nor published in the open literature, M. Vogt, under the guidance of his Ph.D. advisor, W. Keim, of the Rheinisch-WestflUischen Technischen Hochschule in Aachen, Germany, presented the first conceptual aspects of the FBC approach with an emphasis on oligomerization of alkenes, oxidation of alkenes, hydroformylation of olefins, and telomerization of dienes (5, 4). 

Sbodio JI, Lodish HF, Chi NW. Tankyrase-2 oligomerizes with tankyrase-1 and binds to both TRFl (telomere-repeat-binding factor 1) and IRAP (insulin-responsive aminopeptidase). Biochem J 2002 361(Pt 3) 451-9. 

The telomerization reactions are thought to occur by the mechanism in Scheme 22.20. In this mechanism, the two dienes couple to form the tethered alkyl allyl complex. The isolation of this class of complex was reported by Jolly and Wilke during mechanistic studies of diene oligomerization and later by others. Reaction of this complex with methanol would then protonate the olefinic C-3 carbon, and the resulting methoxide would attack the terminal position of the coordinated allyl to generate the resulting diene complex. Replacement of the dienyl ether ligand by two equivalents of butadiene restarts the catalytic process. 

Ethylene provides a good example of a petrochemical feedstock for the synthesis of lipids and polyketides. It can be oligomerized to provide a variety of alkenes into which functionalization can be introduced by hydration, oxidation, hydroformylation, and so on. Of course, telomerization can be used to provide functionalized materials directly. 

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