Ruthenium heterogenization

Catalytic hydrogenation is mostly used to convert C—C triple bonds into C C double bonds and alkenes into alkanes or to replace allylic or benzylic hetero atoms by hydrogen (H. Kropf, 1980). Simple theory postulates cis- or syn-addition of hydrogen to the C—C triple or double bond with heterogeneous (R. L. Augustine, 1965, 1968, 1976 P. N. Rylander, 1979) and homogeneous (A. J. Birch, 1976) catalysts. Sulfur functions can be removed with reducing metals, e. g. with Raney nickel (G. R. Pettit, 1962 A). Heteroaromatic systems may be reduced with the aid of ruthenium on carbon. 

The coordination of ligands at the surface of metal nanoparticles has to influence the reactivity of these particles. However, only a few examples of asymmetric heterogeneous catalysis have been reported, the most popular ones using a platinum cinchonidine system [65,66]. In order to demonstrate the directing effect of asymmetric ligands, we have studied their coordination on ruthenium, palladium, and platinum nanoparticles and the influence of their presence on selected catalytic transformations. 

The most widely used method for adding the elements of hydrogen to carbon-carbon double bonds is catalytic hydrogenation. Except for very sterically hindered alkenes, this reaction usually proceeds rapidly and cleanly. The most common catalysts are various forms of transition metals, particularly platinum, palladium, rhodium, ruthenium, and nickel. Both the metals as finely dispersed solids or adsorbed on inert supports such as carbon or alumina (heterogeneous catalysts) and certain soluble complexes of these metals (homogeneous catalysts) exhibit catalytic activity. Depending upon conditions and catalyst, other functional groups are also subject to reduction under these conditions. 

The synthesis and olefin metathesis activity in protic solvents of a phosphine-free ruthenium alkylidene bound to a hydrophilic solid support have been reported. This heterogeneous catalyst promotes relatively efficient ring-closing and cross-metathesis reactions in both methanol and water.200 The catalyst-catalyzed cross-metathesis of allyl alcohol in D20 gave 80% HOCH2CH=CHCH2OH. 

Kotani, M., Koike, T., Yamaguchi, K. and Mizuno, N. (2006) Ruthenium hydroxide on magnetite as a magnetically separable heterogeneous catalyst for liquid-phase oxidation and reduction. Green Chemistry, 8 (8), 735-741. 

Several ruthenium systems catalyze the hydrogenation of aromatic rings, and this topic is detailed in Chapter 16. An early example reported by Bennett and coworkers was that of RuHCl( 76-C6Me6)(PPh3), which catalyzed the hydrogenation of benzene to cyclohexane at 25 °C, 1 bar H2 [69]. Since ruthenium colloids are very active for this reaction under certain conditions, there is evidence that at least some of the reported catalysts are heterogeneous [70]. 

Typically, heterogeneous transfer hydrogenations are carried out at higher temperatures. The Noyori-Ikariya ruthenium arene catalysts are stable up to temperatures around 80 °C, whilst the rhodium and iridium CATHy catalysts are... 

Raney predicted that many other metal catalysts could be prepared with this technique, but he did not investigate them [8], Copper and cobalt catalysts were soon reported by others [4,5], These catalysts were not nearly as active as Raney s nickel catalyst and therefore have not been as popular industrially however they offer some advantages such as improved selectivity for some reactions. Skeletal iron, ruthenium and others have also been prepared [9-13], Wainwright [14,15] provides two brief overviews of skeletal catalysts, in particular skeletal copper, for heterogeneous reactions. Table 5.1 presents a list of different skeletal metal catalysts and some of the reactions that are catalyzed by them. 

S. L. Buell and J. N. Demas, Heterogeneous preparation of singlet oxygen using an ion exchange boundtris(2,2 -bipyridine)ruthenium(II) photosensitizer, /. Phys. Chem. 87, 4675 1681 (1983). 

A similar study was performed on ruthenium-modified myoglobins, in which AG variations were obtained by changing the nature of the ruthenium complex covalently bound to the protein, and by substituting a porphyrin to the heme [137]. It is gratifying to observe that, in spite of the rather heterogeneous character of this series, the study leads to an estimation of 1.9 to 2.4 eV for A which is consistent with the value 2.3 eV derived in section 3.2.1 from temperature dependent experiments. Satisfactory agreement between the results given by the two methods is also observed in the case of ruthenium-modified cytochrome c [138]. 

Ruthenium Tris-bypyridine/Zeolite-Y/Titanium Dioxide Nano-Assembly Ship-in-a-Bottle Synthesis and Applieation in Heterogeneous Photodegradation of 2,4-xylidine... 

K. Yamaguchi, N. Mizuno, Supported Ruthenium Catalyst for the Heterogeneous Oxidation of Alcohols. Chem. 41 (2002) 4538-4531. 

The formation of P-hydroxyaldehydes from propargylic alcohols has also been observed in aqueous media in the presence of a catalytic amount of water-soluble ruthenium sulfophthalocyanine complex and the heterogeneous ruthenium hydroxyapatite catalyst [40]. 

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