Pd and Ru complexes

Palladium acetate catalyzes the oxidation (acetoxylation) of phenyl acetate to phenylene diacetates (61) and diacetoxybiphenyls (62) [137]. 

According to preliminary data, phenol can be converted to hydroquinone in the presence of the dioxo species trans-Ru(TMP)(0)  

Cobalt(II) complexes of Schiff-bases, Co(salen) and its analogs, have been the most widely used catalysts in mechanistic studies, but ligands with only N-donor atoms (polyamines, porphyrins, etc.) also form catalytically active cobalt(II) complexes. 

Although there may be differences in the detailed mechanisms for individual systems, the catalytic oxygenation of hindered phenols exhibits the following general features. 

The cobalt(II) Schiff base catalyst forms a superoxocobalt(III) complex which converts the phenol into an aryloxy radical, itself being transformed into free or coordinated HO radical  

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Figure 6 Pd and Ru complexes featuring pendant Lewis acids...

An activated carbon was functionalized using nitric acid and the surface acidity was evaluated by Boehm s titrations and XPS. Chosen Pd and Ru complexes were then grafted onto the unmodified and the modified carhon supports. After thermal activation, the obtained Pd-Ru/C catalysts were tested in a selective hydrogenation reaction. The amount of metal grafted in the final catalysts was measured by ICP and seemed to be correlated to the surface acidity. Results from catalytic testing in the hydrogenation of... 

Rh(I) bound metalladendrimers catalyze the hydrogenation of decene with activities similar to the monomeric adduct, and the catalytic dendrimer can be easily separated and recycled. Such a behavior was also pointed out with other phosphorus-containing dendrimers complexes (Pd and Ru complexes) [cf. Sect. 5.3]. 

Rapid hydrogen releases can be achieved under mild conditions by using transition metal complexes as catalysts. Some noble metal complexes, including Pt, Pd, Rh, Ir, and Ru, were proven to be very effective for promoting hydrogen release from AB. The Rh, Pd, and Ru complexes could catalyze AB to dehydrogenate at room temperature with suppressing the release of volatile cyclotriborazane, borazine, and poly(iminoborane) [107]. The iridium pincer... 

Another useful C—C bond-forming reaction is hydrocaiboxylation of olefins using carbon monoxide and water or alcohols (7IS). Under the influence of Ni, Co, Pd, or Ru complexes, hydrogen and carboxyl or... 

The term intramolecular enyne metathesis describes two types of processes. One involves a [2+2] cycloaddition of a multiple bond and a transition-metal carbene complex and the other is an oxidative cyclization catalyzed by low-valent transition-metal complexes, for example, Pt, Pd and Ru. The latter reaction is also called a skeletal reorganization. Both processes lead to similar products (Eq. 84). 

Disubstituted furans with a cyclopropane subunit at the 5-position were synthesized through metal-catalyzed cyclization of l-benzoyl-d.s-l-buten-3-yne derivatives in high yield. Many types of metal complexes, such as Mo, W, Ru, Rh, Pd and Pt complexes were suitable catalysts <02JA5260>. 

Pd, Pt, Rh, and Ru complexes were used as catalysts for the hydrogenation of alkenes with molecular hydrogen. In many cases, higher activity and enhanced selectivity for the desired reaction were accompanied hy successful re-use of the ionic liquid and the catalyst. Examples are reported for cyclohexadiene [10],... 

Although the NH proton is weakly acidic, they can be deprotonated by strong bases, and the mono- or dianionic ligands are found in a variety of di- and trinuclear Mo, W, Ru, Rh, Ir, Pd, and Pt complexes.30-40 Few of them are mononuclear,36,37,40 and in such cases the two napy nitrogen atoms form the chelate ring. However, the mononuclear and a dinuclear complex of identical composition may be in equilibrium in solution, and they can even be crystallized independently as two polymorphs,37 as shown by [Rh(OMe2napy)(cod)]n=12. 

Catalytic symmetric synthesis of P-stereogenic phosphines by cross-coupling of secondary phosphines with benzyl or other alkyl halides was promoted by chiral ft and Ru complexes [112-114]. The key step is believed to be the nucleophilic attack of a metal-phosphido complex on a free electrophile the background reaction of the unactivated nucleophilic substrate is much slower. The origin of enantioselec-tivity, as in the Pd-catalyzed asymmetric cross-couplings described above, is the interconversion of diastereomeric phosphido complexes, whose speciation and relative rates of nucleophilic attack determine the product ratio. In the case of ft ((R./ )-Me-DuPhos)(Ph)(PMels), as with the Pd analog in Scheme 43 above, the major product phosphine was formed from the major diastereomeric phosphido complex (Scheme 63) [112-113]. 

Figure 2.11. The complexity of the catalytic center in its reaction environment is illustrated here with a schematic of the hydgrogenation of glucose over carbon-supported Pd particles that are alloyed with Ru in an aqueous medium. The interaction between the metal and the support, the surface composition of Pd and Ru and possible nucleation of Ru clusters, the aqueous medium and its wetting of the metal and the support, the presence of other metal and support surface intermediates such as hydroxyl groups can all act to influence the catalytic reaction.

Moderate to low energy An, Pt, Pd, Ir and Ru complexes which are phosphorescent at room temperatures with hfetimes typically 1-20 ps, some of which are commercially available (6.2, 6.6-6.8). 

Many interesting reactions and catalytic applications are known especially for Pd and Ru pincer complexes [7]. Ir and Rh pincer complexes are less common, but for some catalytic applications that require high temperatures, such as alkane dehydrogenation, pincer complexes seem to be irreplaceable [8]. 

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