Olefin oligomerization alkene

Formation of C8 alkanes in the alkylation of isobutane even when it reacts with propene or pentenes is explained by the ready formation of isobutylene in the systems (by olefin oligomerization-cleavage reaction) (Scheme 5.2). Hydrogen transfer converting an alkane to an alkene is also a side reaction of acid-catalyzed alkylations. Isobutylene thus formed may participate in alkylation Cg alkanes, therefore, are formed via the isobutylene-isobutane alkylation. 

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). 

Alkene complexes of Ti, Zr and Hf have been intensively investigated with regard to the nature of bonding and the close relation to olefin oligomerization and polymerization. Alkene complexes of zirconocene and hafnocene are isolated as the trimethylphosphine adduct, Cp2M(T -alkene)(PMe3) (33) [92-94]. Cp 2Ti(CH2=CH2) (34) is a 16 electron ethylene complex with a rich reaction chemistry as summarized in Scheme 6.4 [95-99]. The reaction profile of 34 indicates that the metallacyclopropane canonical form makes an important contribution [100]. 

Olefins and acetylenes do not furnish stable substitution products of the composition [M2(CO)io cLx] where L = alkene or alkyne, although it is assumed that these products are formed in olefin oligomerization and polymerization reactions. 

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]. 

Alkenes. At present alkene isomerization is an important step in the production of detergent alkylates (Shell higher olefin process see Sections 12.3 and 13.1.3).264 265 Ethylene oligomerization in the presence of a nickel(O) catalyst yields terminal olefins with a broad distribution range. C4-C6 and C2o+ alkenes, which are not suitable for direct alkylate production, are isomerized and subsequently undergo metathesis. Isomerization is presumably carried out over a MgO catalyst. 

In a recent example, Mironov used the rational replacement of starting materials for oligomerization reactions to discover new MCRs in a systematic way [31]. A reaction library of six alkenes/alkynes, two isonitriles, two nitriles and isoquinoline was set up, giving (n1 — n)/2 different reactions products. A minimum peak height of 30% of the total reaction product was used as a criterion for identifying an efficient MCR. In this way, a novel MCR that yields pyrrolo[2,l-a]isoquinolin-1-ones from electron-deficient olefins, isonitriles and isoquinoline was found (Scheme 10.6). 

The pioneer work in this field was carried out on polystyrene-supported acid catalysts [161]. Thereafter, several works on the use of sulfonic, strong acidic cation exchangers as acid catalysts were reported for alkylation, hydration, etherification, esterification, cleavage of ether bonds, dehydration, and aldol condensation [162,168-171], Besides, industrial applications of these materials were evaluated with reactions related to the chemistry of alkenes, that is, alkylation, isomerization, oligomerization, and acylation. [163,169], Also, Nation, an acid resin which has an acid strength equivalent to concentrated sulfuric acid, can be applied as an acid catalyst. It is used for the alkylation of aromatics with olefins in the liquid or gas phases and other reactions however, due to its low surface area, the Nation resin has relatively low catalytic activity in gas-phase reactions or liquid-phase processes where a nonpolar reactant or solvent is employed [166],... 

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