Oligomerization of olefins

The reiteration of the insertion step of unsaturated compounds into metal-alkyl bonds leads to polymerizations, dealt with in Chapter 7. However a series of important commodities, mainly used as monomers for polymerization, are manufactured by catalytic processes based on early termination steps of sequential olefin additions. 

Shell manufactures a-olefins from ethylene by oligomerization with a nickel catalyst in a polar solvent such as ethylene glycol, under the conditions specified in Equation 27. This corresponds to the first part of the SHOP process (Shell Higher Olefin Process) described in Section 6.2.2. The world production is estimated to be over 1 Mt/a. 

C12 Cig ot-olefins are distilled out and used directly for the manufacture of detergents, while C4-C10 olefins and those C20 undergo isomerization and metathesis as described in Chapters 3 and 6, respectively, to obtain suitable C10-C14 fractions. 

The oligomerization product thus formed is a mixture of olefins with a Schulz-Flory distribution of molecular weights (see also Section 4.7.2), whose composition can be modified, for example by adding an excess of tertiary phosphine or by changing the ancillary ligand. 

A similar catalytic process (Dimersol, Institut Frangais du Petrole), based on a nickel hydride formed in situ from a nickel complex and an aluminium alkyl, has been applied industrially to oligomerize ethylene, propylene, butenes or mixtures of the three. 

10 cSt at 100 °C) and high viscosity ranges. PAOs are carefully designed synthetic oils that are highly branched isoparaffins, oligomerized from alpha olefins. Typically, the alpha olefin of choice is 1-decene. 

CPChem s Synfluid PAO 25 cSt, which is produced with the ionic liquid catalyst has a viscosity at 100 °C, which is unique to the industry. Prior to this product, a 25 cSt PAO was only available commercially by blending higher and lower viscosity PAOs. The specific applications for this product are typically gear oils, greases and various industrial lubricants. 

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Base catalysis is most effective with alkali metals dispersed on solid supports or, in the homogeneous form, as aldoxides, amides, and so on. Small amounts of promoters form organoalkali comnpounds that really contribute the catalytic power. Basic ion exchange resins also are usebil. Base-catalyzed processes include isomerization and oligomerization of olefins, reactions of olefins with aromatics, and hydrogenation of polynuclear aromatics. 

Examples of the unique insights obtained by solid state NMR applications to materials science include the Si/Al distribution in zeolites, the hydrogen microstructure in amorphous films of hydrogenated silicon, and the mechanism for the zeolite-catalyzed oligomerization of olefins. ... 

The Ni-catalyzed oligomerization of olefins in ionic liquids requires a careful choice of the ionic liquid s acidity. In basic melts (Table 5.2-2, entry (a)), no dimerization activity is observed. FFere, the basic chloride ions prevent the formation of free coordination sites on the nickel catalyst. In acidic chloroaluminate melts, an oligomerization reaction takes place even in the absence of a nickel catalyst (entry (b)). FFowever, no dimers are produced, but a mixture of different oligomers is... 

Heterogeneous catalysts for the dimerization and oligomerization of olefins have been known for many years. A considerable number of papers have dealt with the problem of nickel-containing catalysts for ethylene dimerization [1-3]. 

The 7r-back donation stabilizes the alkene-metal 7c-bonding and therefore this is the reason why alkene complexes of the low-valent early transition metals so far isolated did not catalyze any polymerization. Some of them catalyze the oligomerization of olefins via metallocyclic mechanism [25,30,37-39]. For example, a zirconium-alkyl complex, CpZrn(CH2CH3)(7/4-butadiene)(dmpe) (dmpe = l,2-bis(dimethylphosphino)ethane) (24), catalyzed the selective dimerization of ethylene to 1-butene (Scheme I) [37, 38]. 

In the present chapter an attempt is made to summarize the available material concerning the control of selectivity in the nickel-catalyzed homogeneous oligomerization of olefins and related reactions [for a previous review of this topic, see Bogdanovic et al. (4)]. No attempt has, however, been made to give a complete literature survey. 

METHODS OF PREPARATION AND SOME FEATURES OF NICKEL CATALYSTS ACTIVE FOR THE OLIGOMERIZATION OF OLEFINS AND RELATED REACTIONS1... 

The behavior of 3 toward ether or amines on the one hand and toward phosphines, carbon monoxide, and COD on the other (Scheme 2), can be qualitatively explained on the basis of the HSAB concept4 (58). The decomposition of 3 by ethers or amines is then seen as the displacement of the halide anion as a weak hard base from its acid-base complex (3). On the other hand, CO, PR3, and olefins are soft bases and do not decompose (3) instead, complexation to the nickel atom occurs. The behavior of complexes 3 and 4 toward different kinds of electron donors explains in part why they are highly active as catalysts for the oligomerization of olefins in contrast to the dimeric ir-allylnickel halides (1) which show low catalytic activity. One of the functions of the Lewis acid is to remove charge from the nickel, thereby increasing the affinity of the nickel atom for soft donors such as CO, PR3, etc., and for substrate olefin molecules. A second possibility, an increase in reactivity of the nickel-carbon and nickel-hydrogen bonds toward complexed olefins, has as yet found no direct experimental support. 

In principle pentadienyls can bond to transition elements in at least three basic ways, tj3, and tjs (Fig. 1). These can be further subdivided when geometrical factors are considered. If r 5 coordination could be converted to rj3 orr/1, one or two coordination sites could become available at the metal center, and perhaps coordinate substrate molecules in catalytic processes. Little is known about the ability of pentadienyl complexes to act as catalysts. Bis(pentadienyl)iron derivatives apparently show naked iron activity in the oligomerization of olefins (144), resembling that exhibited by naked nickel (13). The pentadienyl groups are displaced from acyclic ferrocenes by PF3 to give Fe(PF3)5 in a way reminiscent of the formation of Ni(PF3)4 from bis(allyl)nickel (144). 

Reaction mechanisms have been proposed for oligomerization of olefins that involve a cationic mechanism initiated by Lewis or Brpnsted acid sites.[19] In the first case, a cationic intermediate is formed and the products obtained are mainly branched oligomers (Scheme 6.1). 

Catani, R., Mandreoli, M., Rossini, S. and Vaccari, A. Mesoporous catalysts for the synthesis of clean diesel fuels by oligomerization of olefins. Catal. Today, 2002, 75, 125-131. 

The feverish interest in hydrido complexes has, as its main cause, the tremendous potential of these reactions in catalytic systems. In a relatively short span of time, hydrido complexes have been found to play a role in a significant number of catalytic processes (6, 9)—e.g., oligomerization of olefins (rhodium), decarboxylation reactions (rhodium), and hydrogenation reactions (ruthenium, osmium, rhodium, iridium, and platinum). Discussion of these applications would go beyond the scope of the present treatment. 

W. Keim, B. Hoffmann, R. Lodewick, M. Peuckert, G. Schmitt, J. Fleischhauer, andU. Meier, Linear Oligomerization of Olefins via Nickel Chelate Complexes and Mechanistic Considerations Based on Semiempirical Calculations, J. Mol. Catal. 6, 79-97 (1979). 

The catalytic oligomerization of olefins in the presence of OAC and the olefin polymerization in the presence of transition metals are based on similar olefin insertions into the metal-carbon and metal-hydrogen bonds (see Section 3.2). However, in organoaluminium compounds, the structure of the active center is defined more simply and more reliably. Data on its coordination state, thermodynamic and kinetic parameters have been reported (e.g. Table 13). 

Over the last 50 years numerous reactions of organic compounds catalyzed by transition metal complexes have been developed (e. g., olefin oxidation -Wacker Process, hydroformylation, carbonylation, hydrogenation, metathesis, Ziegler-Natta polymerization and oligomerization of olefins) in which the reactivity of metal-carbon bonds in the active intermediate (organometallics) is crucial. 

The oligomerization of olefins is mostly catalyzed by cationic complexes which are very soluble in ionic liquids. The Pd-catalyzed dimerization of butadiene [36] and the Ni-catalyzed oligomerization of short-chain olefins [5, 37], which is also known as the Difasol process [1 d] if chloroaluminate melts are used, can be mn in imidazolium salts 1 [38, 39]. Here, the use of chloroaluminate melts and toluene as the co-solvent is of advantage in terms of catalyst activity, product selectivity, and product separation. Cp2TiCl2 [6] and TiCU [40] in conjunction with alkylaluminum compounds were used as catalyst precursors for the polymerization of ethylene in chloroaluminate melts. Neither Cp2ZrCl2 nor Cp2HfCl2 was catalytically active under these conditions. The reverse conversion of polyethylene into mixtures of alkanes is possible in acidic chloroaluminate melts without an additional catalyst [41]. 

G. Parshall, Oligomerization of Olefins, Homogeneous Catalysis, McGraw Hill, New York, pp 56-63, 1980. 

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