Ruthenium compounds reactions

Although the actual reaction mechanism of hydrosilation is not very clear, it is very well established that the important variables include the catalyst type and concentration, structure of the olefinic compound, reaction temperature and the solvent. used 1,4, J). Chloroplatinic acid (H2PtCl6 6 H20) is the most frequently used catalyst, usually in the form of a solution in isopropyl alcohol mixed with a polar solvent, such as diglyme or tetrahydrofuran S2). Other catalysts include rhodium, palladium, ruthenium, nickel and cobalt complexes as well as various organic peroxides, UV and y radiation. The efficiency of the catalyst used usually depends on many factors, including ligands on the platinum, the type and nature of the silane (or siloxane) and the olefinic compound used. For example in the chloroplatinic acid catalyzed hydrosilation of olefinic compounds, the reactivity is often observed to be proportional to the electron density on the alkene. Steric hindrance usually decreases the rate of... 

The ruthenium compounds described above show a distinctly lower metathetic activity than the molybdenum alkenylidene complex 24 developed by Schrock et al. (Fig. 4, see also the chapter by R.R. Schrock, this volume) [18], which is another standard catalyst for any type of olefin metathesis reaction. However, they... 

DR. THOMAS MEYER (University of North Carolina) Wagner de Giovanni, in my lab, is studying the reaction between an oxo ruthenium compound and N0 ... 

Ruthenium compounds are also active catalysts.157 For example [(C6Me6)RuCl2]2 efficiently reduces arenes. Transfer hydrogenation, in which the hydrogen comes from the solvent (e.g. Pr OH) is, also commonly observed.159 Carbonylation reactions such as hydroformylation7 are of great commercial importance.138... 

Transition-metal catalysis, especially by copper, rhodium, palladium and ruthenium compounds, is another approved method for the decomposition of diazo compounds. It is now generally accepted that short-lived metal-carbene intermediates are or may be involved in many of the associated transformations28. Nevertheless, these catalytic carbene transfer reactions will be fully covered in this chapter because of the close similarity in reaction modes of electrophilic carbenes and the presumed electrophilic metal-carbene complexes. 

The oxidation of benzoin with cerium(IV) in perchloric acid solution is proposed to involve an interaction between Ce4+(aq.) ions and the keto alcohol, resulting in the formation of free radicals. The final product is benzoic acid.66 The rate of oxidation of crotyl alcohol with cerium(IV) is independent of the concentration of Ce(IV). The reaction induced polymerization of acrylonitrile indicating the formation of free radicals. The kinetics and activation parameters for the reaction have been determined.67 For the Ir(III)-catalysed oxidation of methyl ketones68 and cyclic ketones69 with Ce(IV) perchlorate, successive formation of complex between the reductant and Ce(IV) and then with the catalyst has been proposed. Results showed that in acidic solutions, iridium(III) is a more efficient catalyst than osmium and ruthenium compounds. 

Ruthenium catalysts found many applications in C-C bond formation reactions (selected reviews [157-161]). Ruthenium occurs mostly in oxidation states +2 and +3, but lower as well as higher oxidation states can easily be reached. Thus ruthenium compounds are frequently used in oxidative transformations proceeding by either single or two electron transfer pathways (selected reviews [162-164]). It has long been known that ruthenium complexes can be used for the photoactivation of organic molecules (selected reviews [165, 166]). Ruthenium complexes are applied as catalysts in controlled or living radical polymerizations [167-169]. 

Ruthenium-catalyzed reactions involving diynes generally lead to the intramolecular oxidative coupling of the two C=C bonds. Bicyclic compounds can be synthesized in the presence of another unsaturated molecule. 

Ruthenium compounds are widely used as catalysts for hydrogen-transfer reactions. These systems can be readily adapted to the aerobic oxidation of alcohols by employing dioxygen, in combination with a hydrogen acceptor as a cocatalyst, in a multistep process. For example, Backvall and coworkers [85] used low-valent ruthenium complexes in combination with a benzoquinone and a cobalt Schiff s base complex. The proposed mechanism is shown in Fig. 14. A low-valent ruthenium complex reacts with the alcohol to afford the aldehyde or ketone product and a ruthenium dihydride. The latter undergoes hydrogen transfer to the benzoquinone to give hydroquinone with concomitant... 

Abstract Ruthenium holds a prominent position among the efficient transition metals involved in catalytic processes. Molecular ruthenium catalysts are able to perform unique transformations based on a variety of reaction mechanisms. They arise from easy to make complexes with versatile catalytic properties, and are ideal precursors for the performance of successive chemical transformations and catalytic reactions. This review provides examples of catalytic cascade reactions and sequential transformations initiated by ruthenium precursors present from the outset of the reaction and involving a common mechanism, such as in alkene metathesis, or in which the compound formed during the first step is used as a substrate for the second ruthenium-catalyzed reaction. Multimetallic sequential catalytic transformations promoted by ruthenium complexes first, and then by another metal precursor will also be illustrated. 

A number of different ionic liquids have been screened in the ruthenium-catalysed oxidation of secondary alcohols (see Scheme 5.18). Three different ruthenium compounds, RuC13, RuCl2(PPh3)3 and [RuCFl/i-cymene) were compared and best results were obtained with RuCl2(PPh3)3.[76] While imidazolium-based ionic liquids gave only poor results (anion = Cl) or suppressed the reaction completely (anion = [BF4] or [PF6] ), tetraalkylammonium-based solvents such as Aliquat 336 (tricaprylmethylammonium chloride) or tetramethylammonium hydroxide afforded much better yields. 

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