Ruthenium complexes mononuclear

Mononuclear ruthenium complexes were found to be superior to carbonyl clusters during a comprehensive comparison of a variety of catalysts in the reduction of acetone [49]. Without solvent, most catalysts were highly selective, although the activity was quite low. The addition of water to the system vastly increased yields, in agreement with Schrock and Osborrfs observations into rhodium-catalyzed hydrogenations (Table 15.9) [41],... 

Quite recently, some mononuclear ruthenium complexes such as [(p-cymene)RuX-(CO)(PR3)]OTf (X = Cl, OTf, R = Ph, Cy) have been found to work as catalysts for the propargylation of aromatic compounds such as furans, where some ruthenium complexes were isolated as catalytically active species from the stoichiometric reactions of propargylic alcohols (Scheme 7.27) [31]. The produced active species promoted the propargylation of furans vdth propargylic alcohols bearing not only a terminal alkyne moiety but also an internal alkyne moiety, indicating that this propargylation does not proceed via allenylidene complexes as key intermediates. 

Mononuclear ruthenium complexes have become useful catalysts, not only because they can have high regio- and stereoselectivity but also because their catalyzed reactions rely on an elucidated mechanism. This true for the cis-dihydride (PP3)RuH2 complex, a catalyst precursor for the selective head-to-head dimerization of phenylacetylene to the corresponding (Z)-enyne, via bis(alkynyl) active spe-... 

Subsequently, many other mononuclear ruthenium complexes were successfully tested as catalysts (Fig. 37). Several catalyst classes were reviewed recently... 

RuCl2(PMe3)(C6Me6) and RuCl2(PMe3)(p-cymene) appear to be much more efficient catalysts than other mononuclear ruthenium complexes, or Ru3(CO)12, for a variety of secondary amines and terminal alkynes, such as diethylamine, morpholine, piperidine, and pyrrolidine (65,201), except for acetylene itself (202,203). The regioselective addition to the terminal carbon suggests that that the reaction proceeds via an arene ruthenium vinyl-idene intermediate that has been characterized (66) (Section II,A,3,d). 

As a general preparation procedure of the water oxidation catalyst of dinuclear ruthenium complex, [(bpy)2(H20)Ru0Ru(H20)(bpy)2], the corresponding mononuclear ruthenium complex ds-[Ru(bpy)2(H20)2] has been used as a precursor complex . However, other reports claimed that the mononuclear ruthenium complex itself can mediate water oxidation under... 

Although ruthenium is significantly less expensive than rhodium and although its use has been recommended since 1960 (7) for the oxo synthesis, complexes of this metal have not been developed as catalysts. However, many papers and patents have referred to the results obtained employing various ruthenium complexes. The purpose of this article is to analyze the work done involving ruthenium compounds, restricting the scope only to the hydroformylation reaction and not to the carbonylation reaction, which would demand to too lengthy an article. In this review we examine successively mononuclear ruthenium complexes, ruthenium clusters as precursors, photochemical activation, and supported catalysis. 

Special interest was focused on the photochemistry and redox properties of mononuclear ruthenium complexes.20 Examples show the nucleophilic attack of one of the N atoms of 1,8-naphthyridine on the coordinated CO in [Ru(bipy)2(napy)(CO)]2+ upon le reduction of the napy moiety (Scheme 2). Such a type of metallacyclization enables the reduction of the CO group, derived from the electrochemical reduction of C02 catalyzed by [Ru(bipy)(napy)2(CO)2](PF6)2, to produce acetone in the presence of Me4NBF4.21,22 An unusual result is the simultaneous formation of a carbene ligand and the addition of the methoxo group to the naphthyridine ring upon reaction of [Ru(bipy)2(napy)]2+ with propiolic acid in methanol (Scheme 2).23... 

The mechanism of this interesting reaction is also discussed. Since kinetic studies suggest that the rate-determining step of the catalysis is C H activation of pyridine, this reaction requires an excess of pyridine. An active key intermediate depicted below is isolable (Figure 10.3). Although a mononuclear ruthenium complex cannot be ruled out as the active catalyst, the cluster framework remains intact during the course of the catalysis. 

Ruthenium complexes having cyclopentadienyl ligands have also been extensiveK investigated. Because ruthenocene is relatively unreactive, much attention has been focused on mononuclear ruthenium complexes with one cyclopentadienyl ligand or ruthenium dimers having cyclopentadienyl ligands. 

Dehydration of propargyl alcohols occurs commonly on mononuclear ruthenium complexes.[ l Water is formed from the terminal alkynic hydrogen and by the alcoholic OH this is the more common dehydration process (it is denoted Route A). These reactions afford organic intermediates leading to cumulene complexes useful for the synthesis of doped polyacetylenes or of non-linear optic materials. Dehydration of rhodium-coordinated propargyl alcohols " leads to free or coordinated cumulenes and can be catalyzed by alumina and chloride ions, Fig. 16. 

The literature contains several examples of deprotonation of dipropargyl alcohols on mononuclear ruthenium complexes leading to dimeric derivatives linked by five... 

Ru3(CO)i2 [23] and more efficiently mononuclear ruthenium complexes [24] catalyze the a f -Markovnikov addition of ammonium carbamates generated in situ from secondary amines and carbon dioxide to terminal alkynes, and selectively produce vinyl carbamates with the (Z)-product as major stereoisomer (Scheme 6) [24-26]. 

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