Olefin dimerization catalysts

Should an olefin dimerization catalyst have an electron-rich or electron-poor metal center. Why Example ... 

Butene. Commercial production of 1-butene, as well as the manufacture of other linear a-olefins with even carbon atom numbers, is based on the ethylene oligomerization reaction. The reaction can be catalyzed by triethyl aluminum at 180—280°C and 15—30 MPa ( 150 300 atm) pressure (6) or by nickel-based catalysts at 80—120°C and 7—15 MPa pressure (7—9). Another commercially developed method includes ethylene dimerization with the Ziegler dimerization catalysts, (OR) —AIR, where R represents small alkyl groups (10). In addition, several processes are used to manufacture 1-butene from mixed butylene streams in refineries (11) (see BuTYLENEs). 

In addition to a-additions to isocyanides, copper oxide-cyclohexyl isocyanide mixtures are catalysts for other reactions including olefin dimerization and oligomerization 121, 125, 126). They also catalyze pyrroline and oxazoline formation from isocyanides with a protonic a-hydrogen (e.g., PhCH2NC or EtOCOCHjNC) and olefins or ketones 130), and the formation of cyclopropanes from olefins and substituted chloromethanes 131). The same catalyst systems also catalyze Michael addition reactions 119a). 

Two-phase systems in which an insoluble organic substrate is reacted with a catalyst dissolved in an ionic liquid show promise for commercial use (Chauvin and Helene, 1995 Freemantle, 1998). One such system is a nickel-catalyzed olefin dimerization. The dimers are produced selectively and decanted from the ionic liquid. The catalyst/ ionic liquid phase is recycled without loss of activity. Other reactions investigated include ... 

Only one olefin dimerization, namely that of ethylene to butene, has been attempted using a supported metal catalyst (58) (Table V). The catalyst, prepared as in the preceeding reaction (34), had nearly the same activity as its homogeneous analog. However, the reaction clearly took place on the catalyst surface since no evidence could be found for any nickel in solution. The presence of a solvent (toluene) was important for the selectivity of the reaction since in its absence considerable amounts of hexenes and octenes were formed. 

For a review of olefin dimerization and oligomerization with all catalysts, see Fel dblyum Obeshchalova Russ. Chem. Rev. 1968,37, 789-797. 

P-31 NMR was a powerful tool in studies correlating the structure of tertiary-phosphine-rhodium chloride complexes with their behavior as olefin hydrogenation catalysts. Triphenylphosphine-rhodium complex hydrogenation catalyst species (1) were studied by Tolman et al. at du Pont and Company (2). They found that tris(triphenylphosphine)rhodium(I) chloride (A) dissociates to tri-phenylphosphine and a highly reactive intermediate (B). The latter is dimerized to tetrakis(triphenylphosphine)dirhodium(I) dichloride (C). 

Treatment of [(CsMe4SiMe2N-t-Bu)Sc(PMe3)(/i-H)]2 with two equivalents of propylene at low temperature yielded the structurally characterized phosphine-free di-p-propyl complex [(C5Me4SiMe2N-t-Bu)Sc(/i-nPr)]2. This dimeric organoscandium alkyl was found to be an even more active a-olefin polymerization catalyst than the hydride precursor [52],... 

A study of the olefin oxidation catalyst system, palladium acetate-MOAc (M = Li or Na), has shown that in the absence of acetate ion, Pd acetate-acetic acid exists as the trimeric species [Pd3(OAc)6].32 Reaction with MOAc is not instantaneous, and u.v.-visible spectra indicate an initial equilibrium involving trimer - dimer (9). When M = Na conversion into dimer is complete at 0.2M-NaOAc. Further addition of... 

The polymerisation proceeds quite slowly, presumably owing to the inactivity of the formally d° 16-electron yttrium species of the dimeric catalyst. A formally d° 14-electron monomeric hydride or alkyl derivative is probably required for olefin polymerisation [187],... 

Susuki and Tsuji reported the first Kharasch addition/carbonylation sequences to synthesize halogenated acid chlorides from olefins, carbon tetrachloride, and carbon monoxide catalyzed by [CpFe(CO)2]2 [101]. Its activity is comparable to or better than that of the corresponding molybdenum complex (see Part 1, Sect. 7). Davis and coworkers determined later that the reaction does not involve homolysis of the dimer to a metal-centered radical, which reduces the organic halide, but that radical generation occurs from the dimeric catalyst after initial dissociation of a CO ligand and subsequent SET [102]. The reaction proceeds otherwise as a typical metal-catalyzed atom transfer process (cf. Part 1, Fig. 37, Part 2, Fig. 7). 

When Ni(II) - NHC complexes contain an alkyl, aryl, or acyl group, reductive elimination can occur, affording Ni(0) compounds and 2-mediated organoim-idazolium salts (Eq. 16). This pathway results in catalyst decomposition for reactions by Ni - NHC systems [45]. In Ni - NHC-catalyzed olefin dimerization, Cavell and Wasserscheid showed that this decomposition is inhibited when reactions are run in ionic liquids rather than more classical solvents such as toluene [46]. 

Only one example of an NHC-containing olefin metathesis catalyst containing a transition metal other than ruthenium has been reported in the literature. The NHC-osmium complexes 53a and 53b (Scheme 2) are synthesized from the dichloro(i]6-p-cymene)osmium dimer by addition of the NHC prepared in situ and abstraction of the chloride, followed by introduction of the ben-zylidene moiety with phenyl diazomethane. 

Copper compounds are catalysts for the Michael addition reaction (249), olefin dimerizations (245, 248), the polymerization of propylene sulfide (142), and the preparation of straight-chain poly phenol ethers by oxidation of 2,6-dimethylphenol in the presence of ethyl- or phenyl-copper (209a). Pentafluorophenylcopper tetramer is an intriguing catalyst for the rearrangement of highly strained polycyclic molecules (116). The copper compound promotes the cleavage of different bonds in 1,2,2-tri-methylbicyclo[1.1.0]butane compared to ruthenium or rhodium complexes. Methylcopper also catalyzes the decomposition of tetramethyllead in alcohol solution (78, 81). 

Olefin oligomerization were found to occur on SAPO molecular sieves, though their activity was far less than the of zeolite ZSM-5[17]. While showing very different initial activity, the wide-pore SAPO-5 and the narrow pore SAPO-34 both deactivated severely (Figure 3). Both of these catalysts yielded a wide spectrum of products presumably following the pathway described by Tabak et. al. [5], in which numerous olefin polymerization and scission reactions take place. Strangely, medium pore SAPO-11 showed complete selectivity for olefin dimers... 

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. 

While rare-earth metals are proven powerful olefin polymerization catalysts [21-24], there are only limited reports on controlled olefin oligomerizations or selective olefin dimerizations utilizing these elements [204,207,208], An ansa-scandocene [207] and the bis(indenyl)yttrium complex 41 (Fig. 25) [204] were reported to produce head-to-tail dimers from monosubstimted aliphatic alkenes (57). Complex 41 produces predominantly the tail-to tail adduct with styrene. The codimerization of an aliphatic alkene (including substrates containing various functionalities) with styrene affords tran -tail-to-tail dimers, apparently as a result of 1,2-insertion of the a-olefin followed by 2,1-insertion of styrene directed by the phenyl group (58). 

The last group are ruthenium complexes having arenes or dienes. These Ti-stabilized complexes are not only used for low valent ruthenium starting materials via replacement of arene or diene ligands but are catalysts for olefin dimerization, hydrogenation of arenes, or C—C bond cleavage reaction. 

Scheme 3.1 Catalysts for olefin dimerization - standard nickel catalyst 1 and its fluorous analog 2 (n = 3-5). In a Hostinert 216 (3)/toluene biphasic system the catalyst stays in the fluorous phase [5] whereas the product dissolves preferably in toluene [4],...

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