Olefins catalyst bond, strength

The major anomaly in olefin reactions is the superior ability of Fe, Co, and Ni to act as hydrogenation catalysts in comparison with expectations based on the strength of olefin bonding in complexes. Olefins are quite strongly chemisorbed by these metals (5) we must therefore infer that the presence of several metal atoms in proximity sometimes confers a binding ability not possessed by single atoms. Whether this effect is of particular importance with these metals or whether it will prove to... 

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],... 

A decisive role may be played by the strength of the bond between olefin and the catalyst (4,47,57). This view is indirectly supported by the degree of stability of organometallic complexes of transition metals with olefinic ligands, which decreases with increasing isomerization ability of the given metal. It may be assumed that the relative adsorptivity of an olefin on the surface of various metals corresponds to the stability of compounds formed by the olefin with salts of the respective metals (62-64). 

The esterification of camphene (2) with acetic acid at a reaction temperature of 80 °C showed a conversion of 88% with a selectivity of 87% with the catalyst SAC 13 and a selectivity of 88% with the Amberlyst A 15. The carboxylic acid was in four-fold molar excess with 10 wt% catalyst. Both, the SAC 13 and the A 15 show high activity (each 88% conversion) and high selectivity in this reaction. This olefinic compound seems to be so reactive as to render high conversion independently of the acid strength of the catalyst. This could be due to the terminal double bond and to the very stable carbocation formed by protonation. 

The ease of addition of the hydrides (e.g. R3MH, M = Si, Ge, Sn, Pb) to alkenes increases down Group IVB as the M—H bonds decrease in strength. Thus trialkylsilanes require heating to about 300°C under olefin pressures of at least 300 atm, UV irradiation, or catalysis by peroxides, certain metal salts or tertiary amines. Trialkylgermanes and trialkylstannanes add to activated terminal carbon-carbon double bonds at 120°C and 90°C respectively and a catalyst is not necessary, e.g. 

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