Oligomerization reaction

The cyclotrimerization of allene in the vapor phase, in the presence of a nickel (o) catalyst, gives a mixture of the shown cyclotrimers 83 and 84 (35 % yield) and the cyclotetramer 85 in 7 % yield Also, the pentamer 86 is isolated in the oligomerization of allene .  

The complexes formed in the reaction of allene with a stoichiometric amount of nickel (o) catalysts readily add another molecule of allene to give trimer complexes, from which a quantitative yield of 1,2,4-trimethylenecyclohexane is obtained . In the oligomerization of allene, mixtures of higher oligomers are often formed, from which the oligomers listed in Table 6.3 were isolated. 

from the nickel (o) complex of 1,2-cyclononadiene upon heating to 60 °C mixtures of trimers and oligomers are formed. From t-butylallene at 290 °C, a mixture of the two aromatic trimers 87 and 88 are formed (see also Section 6.1.2.)  

The reaction of tetramethylallene with isopropylidene carbene affords the [2+1] cycloadduct in 12% yield. Likewise, reaction with dimethylvinylidene carbene 89 affords the [2+1] cycloadduct 90 in 35 % yield  

The allene 91 reacts with diazomethane in the presence of CuCl to give the mono adduct 92 (50 % yield) and the bis-adduct 93 (30 % yield) 

The first synthesis of oligomeric dialkylsilyl carbodiimides 31 dates back to 1964, when Pump and Rochow reacted disilvercyanamide suspended in diethylether or benzene with dialkyldichlorosilanes 30 (R = Me, Ph, OEt R = Me, vinyl, Ph, OEt) the yields varied between 77 and 96 % and n varied between 6.4 and 8.4.  

The reaction of dichloromethylsilane with cyanamide affords a highly crosslinked polymer caused by hydrosilation reactions between the carbodiimide and the Si-H bond. Gels are obtained in the reaction of dimethylchlorosilane with bis(trimethylsilyl)carbodiimide. Using TiCU or Ti(NEt2)4 with bis(trimethylsilyl)carbodiimide produces poly(titanium 

Disilylcarbodiimide polymers 33 are obtained from disilanes 32 and cyanamide in the presence of triethylamine.  

Likewise, tetrachloro-l,2-dimethyldisilane reacts with bis(trimethylsilyl)carbodiimide to give Si/C/N gels. In the reaction of methyltrichlorosilane with bis(trimethylsilyl)carbodi-imide in the presence of pyridine, a highly crosslinked ceramic precursor is also obtained.  

A 16 membered ring carbodiimide is obtained in the reaction of Me2SiCl2 with cyanamide. In addition to the tetramer, oligomers with n = 2 to 7 are detected. Also, higher oligomeric carbodiimides are formed in the reaction of alkyl- and dialkyl silicon chlorides with cyanamide in the presence of pyridine. Also, from bis(trimethylsilyl)carbodiimide and silicon tetrachloride in the presence of pyridine, the silicon polycarbodiimide 34 is obtained.  

---

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). 

A similar reaction occurs with fatty acids (such as stearic acid) or methyl stearate, which undergo isomerization, cracking, dimerization, and oligomerization reactions. This has been used to convert solid stearic acid into the more valuable liquid isostearic acid [102] (Scheme 5.1-70). The isomerization and dimerization of oleic acid and methyl oleate have also been found to occur in chloroaluminate(III) ionic liquids [103]. 

In dimerization and oligomerization reactions, ionic liquids have already proven to be a highly promising solvent class for the transfer of established catalytic systems into biphasic catalysis. 

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... 

The reaction of methanol over a ZSM-5 catalyst could be considered a dehydration, oligomerization reaction. It may be simply represented as ... 

Table 5 gives typical results of the wax cracking process to surfactant olefins. Compared with the pure a-olefins produced by the oligomerization reactions of ethylene the crack olefins are decreased in quality, especially due to the conjugated diene part (2-4%). Moreover, there are some problems in guaranteeing the wanted amounts of C20-C30 n-alkanes. Therefore in industrially de-... 

To select the metal to be incorporated into the substrate porphyrin unit, the following basic properties of metalloporphyrins should be considered. The stability constant of MgPor is too small to achieve the usual oligomeric reactions and purification by silica gel chromatography. The starting material (Ru3(CO)i2) for Ru (CO)Por is expensive and the yield of the corresponding metalation reaction is low. Furthermore, the removal of rutheniirm is difficult, and it is likewise difficult to remove the template from the obtained ruthenium CPOs. Therefore, ZnPor is frequently used as a substrate in this template reaction, because of the low prices of zinc sources (zinc acetate and/or zinc chloride), the high yield in the metalation reaction, the sufficient chemical stability of the ZnPor under con-... 

Although we choose neither method A nor B, difficulties in the purification and/or isolation of CPOs are unavoidable. The component porphyrin unit with polar substituents such as an ester group produces further polar products in oligomerization reactions. The polarities of the products are proportional to the degrees of oligomerization caused by the increase in the number of func-... 

Decomposition of the adsorbed carbenium ions is the main reaction charmel. However, isomerization (aromatization) and oligomerization reactions also proceed, and are the route to coke formation. 

The preparation of the first phosphodiester complexes of platinum(II), in particular those containing the diphenylphosphato ligand, has been reported.139 Treatment of [PtCl2(en)] with Ag20 in DMF with two equivalents of diphenylphosphate gives [Pt(dpp)2(en)] ((26) dpp = diphenylphosphato, en = ethylene- 1,2-diamine), the first example of a bis(phosphodiester) complex of platinum(II). The complex is stable as a monomer, and it does not undergo dimerization or oligomerization reactions. 

Nickel containing MCM-36 zeolite was used as new catalyst in the ethylene oligomerization reaction performed in slurry semi-batch mode. This catalyst, with micro-mesoporous structure, mild acidity and well balanced Ni2+/acid sites ratio, showed good activity (46 g of oligomers/gcataLh) and selectivity (100% olefins with even number of carbon atoms). The NiMCM-36 behaviour was compared to those obtained with NiMCM-22, NiY, NiMCM-41 and NiMCM-48 catalysts. 

A small number of template mediated reactions which afford thioether macrocycles are also known, e.g. the small trithia [9]aneS3 is also obtained in good yield using Mo(CO)3 as a template.73,74 The crown trithioether is readily demetallated by addition of a further equivalent of [NMe4]2[S(CH2)2S(CH2)2S]. Also, dibenzo-[18]aneS6 and dibenzo-[15]aneS5 have been prepared via an iron dicarbonyl template.75,76 Metal-induced cyclo-oligomerization reactions of... 

Polymerization and oligomerization reactions. l-FIalogenopropane-2-thiones give homopolycondensation,10 in different conditions l-chloropropane-2-thi-one11 forms a polymer or a cyclic trimer. a-Oxothioketones12 15 form dimers, by [4+2] unsymmetrical Diels Alder cycloaddition (Scheme 7). a,p-Unsatu-rated thioketones,16 Scheme 3 E = S, form dimers via head-to-head (R1 = Ph, R2 = Me) and head-to-tail (R1 = R2 = Ph), while selenoketones, E = Se, dimerize17 via head-to-head . 

The catalytic cyclo-oligomerization of 1,3-butadiene was first reported by Reed in 1954 using modified Reppe catalysts.4 Wilke et al., however, demonstrated in pioneering, comprehensive and systematic mechanistic investigations, the implications, versatility and the scope of the nickel-catalyzed 1,3-diene cyclo-oligomerization reactions.3,5... 

Although the pioneering, systematic, and comprehensive experimental work of Wilke et al3,5 has led to a thorough understanding of the nickel-catalyzed cyclo-oligomerization reaction of 1,3-butadiene, there are still some essential mechanistic details that are not yet firmly established (vide infra). In the following account, we summarize recent progress in the... 

THEORETICALLY REFINED CATALYTIC CYCLES FOR THE NICKEL-CATALYZED CYCLO-OLIGOMERIZATION REACTIONS OF... 

For PR3/P(OR)3-stabilized nickel complexes, there are two borderline cases known from the experimental investigation of Heimbach et al. 1 which, unlike the usual behavior, redirect the cyclo-oligomerization reaction into the Ci2-cyclo-oligomer production channel. Catalysts bearing either strong a-donor ligands that must also introduce severe steric pressure (e.g., PBu Pr2) or sterically compact n-acceptors (like P(OMe)3) are known to yield CDT as the predominant product. From a statistical analysis it was concluded,8a,8c that the C8 Ci2-cyclo-oligomer product ratio is mainly determined by steric factors (75%) with electronic factors are less important. 

It is apparent from this short introduction that optimal control of the overall selectivity of olefin oligomerization reactions depends on the simultaneous control of several different types of selectivity. 

Evidence has been collected over the years which strongly indicates that the active species in the oligomerization reactions are nickel-hydride and nickel-alkyl complexes. [This is not necessarily true for catalysts prepared from nickel(II) compounds and organoaluminum compounds having low Lewis acidity, e.g., (C2H5)2A10C2H5 (44).] The majority of the evidence is circumstantial and is discussed below. 

Reactions leading to the formation of the catalytically active nickel hydride species from organonickel precursors (Section III) can be regarded as model reactions for olefin oligomerization reactions. The reactions described by Eq. (8) and Scheme 3 (Section III) show that RNiX compounds (R = methyl orallyl, X = halide or acetylacetonate) activated by Lewis acids add to double bonds under mild reaction conditions (-40° or 0°C). It follows further from these reactions that under conditions leading to olefin dimerization a rapid nickel hydride /3-hydrogen elimination reaction occurs. The fact that products resulting from olefin insertion into the nickel-carbon bond are only observed when /3-hydride... 

---