Using a metal catalyst

Asymmetric hydrogenation using a metal catalyst [Ru((S)-BiNAP)].. .. 117... 

In summary, in order to reduce the content of toluene in gasoline while keeping a high octane number, toluene must undergo hydrogenation and ring contraction followed by SRO. The RC step can proceed via bifunctional catalysts and the SRO must use a metal catalyst (e.g. Ir/Si02) that is selective towards the dicarbene mechanism to cleave C-C bonds at unsubstituted positions. 

The generation of a carbene (or when using a metal catalyst, a carbenoid) from an a-diazocarbonyl-componnd, in the presence of a nitrile, resnlts in overall cycloaddition and the formation of an oxazole. Both a-diazo-ketones and a-diazo-esters have been used, the examples in the seqnence below showing that the resnlt in the latter sitnation is the formation of a 5-alkoxy-oxazole. The exact sequence of events is not certain, bnt may involve a nitrile ylide, the result of electrophilic addition of the carbene to the nitrile nitrogen. 

Hydrogenation of benzene under pressure using a metal catalyst such as nickel results in the addition of three molar equivalents of hydrogen and the formation of cyclohexane (Section 14.3). The intermediate cyclohexadienes and cyclohexene cannot be isolated because these undergo catalytic hydrogenation faster than benzene does. 

To achieve the selectivity in the mixture of products with different methylene bridges is a critical issue. It is reported that the selectivity of the p-isomer can be boosted by using P-cyclodextrin or crown ether [4]. The basic mechanism is that the additive form complexes with the phenoxide ions and encourages preferential attack at the p-position due to the steric hindrance caused by the attack at o-position. Ortho selectivity can be increased by using a metallic catalyst such as salts of zinc, magnesium, or lead. When the reaction is carried out in the presence of metallic salts, the metal ion forms... 

Lee HS, Torres Cl, Parameswaran P, Rittmann BE. Fate of H(2) in an upflow single-chamber microbial electrolysis cell using a metal-catalyst-free cathode. Environ Sci Technol 2009 43 7971-7976. 

SCHEME 1.2 Cocatalyzed MCR using a metal catalyst and an organocatalyst along with the proposed mechanism [46]. 

---