Olefin homogeneous catalysts

The activity of homogeneous catalysts also has been demonstrated Wilkin son s catalyst trisftriphenylphosphme rhodium chloride induces perfluoroalkyl iodides to add to olefins at 80 [70] (equation 10) Tetrakis(triphenylphosphine)-... 

The origin of the remarkable stereoselectivities displayed by chiral homogeneous catalysts has occasioned much interest and speculation. It has been generally assumed, using a lock-and-key concept, that the major product enantiomer arose from a rigid preferred initial binding of the prochiral olefin with the chiral catalyst. Halpren 48) on the basis of considerable evidence, reached the opposite conclusion the predominant product enantiomer arises from the minor, less stable diastereomer of the olefin-catalyst adduct, which frequently does not accumulate in sufficient concentration to be detected. The predominant adduct is in essence a dead-end complex for it hydrogenates at a much slower rate than does the minor adduct. 

The oligomerization of the ethylene is performed at 80-120°C and at a pressure of 70-140 bar. A solvent like 1,4-butanediol is used, in which only the catalyst and the monomeric ethylene are soluble but not the formed higher molecular weight olefins. The oligomerization of the ethylene in such a two-phase systems enables the separation of the homogeneous catalyst from the reaction product by a simple phase separation. 

The industrially used homogeneous catalysts for the hydroformylation of higher molecular olefins into aldehydes, which are hydrogenated to the corresponding surfactant alcohols, are cobalt carbonyl [47] or cobalt carbonylItert-phosphine complexes [48]. 

Stack and coworkers immobilized phenantrohne derivative 16 on micelle-templated silica SBA-15 (Scheme 8) [55,56]. The system showed more selective and efficient catalytic activity for olefin epoxidations with peracetic acid than the analogous homogeneous catalyst. 

In the case of functionalized olefins, heterogeneous catalysts have usually not performed well [84,85]. Methyl oleate is the typical test substrate the following order of stability towards the ester functional group for the different SOM catalysts has been observed (based on the number of turnovers) Re W > Mo, which is similar to what has been described for related homogeneous systems. In the specific case of Re, 900 TON can be reached, while TON for other Re-based heterogeneous catalysts do not exceed 200 [79,84]. 

Activation of Molecular Hydrogen by Homogeneous Catalysts S. W. Weller and G. A. Mills Catalytic Syntheses of Ketones V. I. Komarewsky and J. R. Coley Polymerization of Olefins from Cracked Gases... 

Our interest in silicon chemistry quite naturally led to a study of the hydrosilation reaction, the addition of the Si-H group across an olefin or an acetylene. This reaction is one of the most useful methods of making silicon-carbon bonds and is an important industrial process. Typically, homogeneous catalysts based on platinum, rhodium or ruthenium are used, and while very efficient, they are not recoverable(46). 

Immobilization of catalysts is an important process design feature (see Chapter 9.9). A recent example of catalyst immobilization is the biphasic approach which seems superior to immobilization on solids, as successfully proven in the Ruhrchemie/Rhone Poulenc process for the hydro-formylation of olefins.286 Supported liquid phase catalysis was devised as a method for the immobilization of homogeneous catalysts on solids. When the liquid phase is water, a water-soluble catalyst may be physically bound to the solid. 

The molecular design of stereospecific homogeneous catalysts for polymerization and oligomerization has now reached a practical stage, which is the result of the rapid developments in early transition metal organometallic chemistry in this decade. In fact, Exxon and Dow are already producing polyethylene commercially with the help of metallocene catalysts. Compared to the polymerization of a-olefins, the polymerization of polar vinyl, alkynyl and cyclic monomers seems to be less developed. 

Non-metallocene complexes, such as aryloxide 31 and amide 138, have also been utilized as catalyst systems for the polymerization of a-olefins. Moreover, the homogeneous olefin polymerization catalysts have been extended to metals other than those in Group 4, as described in Sect. 7. Complexes such as mono(cyclopentadienyl)mono(diene) are in isoelectronic relationship with Group 4 metallocenes and they have been found to initiate the living polymerization of ethylene. These studies will being further progress to the chemistry of homogeneous polymerization catalysts. 

Only one example was found in which a silicon compound with the structure =SiH2 was added to internal olefins with a homogeneous catalyst, and it gave surprising results (46). Dichlorosilane was added to 2-... 

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