Catalysts organo-metal

Two-component systems are obtained by the interaction of transition metal compounds of groups IV-VIII of the periodic system with or-ganometallic compounds of groups I-III elements (Ziegler-Natta catalysts). An essential feature of the formation of the propagation centers in these catalysts is the alkylation of the transition metal ions by an organo-metallic cocatalyst. 

Supported oxide catalysts were discovered at the same time (8-5) as the two-component Ziegler-Natta catalysts (6, 7) in the early 1950 s. The publications on other types of one-component catalysts [supported organo-metallic compounds of transition elements (8, 9, 9a) and titanium dichloride (10) ] appeared quite recently. 

Water is a highly polar - and hence protic - solvent, the presence of which may strongly influence the chemistry of two-phase aqueous processes. Of course, all components of the reaction mixture should be stable to water, and to this end care must be taken with the choice of catalyst. Today, aqueous organo-metallic catalysis has become a mature field of chemistry, and a very wide choice of water-soluble and water-stable hydrogenation catalysts is available. It should also be borne in mind that water is a reactive solvent and may take part... 

With Cp2Zr(OtBu)(THF) as catalyst, selectivities are generally -20 1 endo exo. See S. Collins, B.E. Koene, R. Rama-chandran, N. J. Taylor, Organo-metallics 1991, 10, 2092—2094. 

In laboratory-scale homogeneous catalysis applications, in the last decade further investigations have been carried out in which a less soluble organo-metallic catalyst system was utilized for metathesis reactions [46]. Under RCM-conditions, it was possible to convert substrates with functional groups that were problematic due to their potential to inactivate the rutheniiun catalyst here, the conversion in supercritical carbon dioxide avoids the protection of critical amino groups as an additional synthetic step. Consequently, it was possible to synthesize a number of carbo- and heterocyclic products with varying ring size (C4 to Cie). 

Metallocene, An organo-metallic coordination compound, or more specifically a cyclopentadienyl derivative of a transition metal or metal halide. Metallocenes are best known as catalysts for polymerizing ethylene and propylene. 

Pincer compounds with a general structure like 20 are common in organo-metallic chemistry [832]. They are useful as precursors to catalysts and as components of hybrid organometallic polymers [84-86]. In most cases, they have high stability to oxygen and water in addition to high thermal stability. 

Polypropylene (PP) is a stereospecific polymer prepared by polymerization using organo-metallic catalyst system. Commercial PPs have up to 95% isotactic content, which means that pendant methyl groups are almost all on the same side of the chain. When PP is exposed to ionizing radiation, free radicals are formed that cause chemical changes. Because PP is highly crystalline, these radicals are relatively immobile and consequently may not be available for reaction for long periods of time.96... 

Bruneau, C., Dixneuf, P. H., Eds., Ruthenium Catalysts and Fine Chemistry (Topics in Organo-metallic Chemistry, No. 11), Springer Verlag, Berlin and Heidelberg, 2004. 

Aromatic compounds are good enough nucleophiles to add in conjugate fashion under Friedel-Crafts conditions so that no organo-metallic reagent is needed. Benzene adds to cinnamic acid 74 with AICI3 as catalyst to give 73 in one step.17... 

Figure 10.8 Examples of non-enzyme catalysed steroselective reactions with (a) a non-organo-metallic catalyst, (b) an organometallic catalyst and (c) a Sharpless-Katsuki catalyst...

The detachment of molecules with concomitant cross-coupling or allylic substitution is an elegant means of increasing diversity on cleavage. A common drawback of most methods is contamination with transition metal catalysts and organo-metallic by-products, although a variety of methods is available for the sequestering of transition metals from the cleaved products. The same applies to removal of other by-products. 

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