Hydrogenation double ruthenium catalyzed

A dominant feature of the type c ring-construction approach to azepine systems has been ruthenium-catalyzed ringclosing metathesis reactions. Examples include the synthesis of the azepine derivative 157 from 156 using either the Grubbs type I catalyst 159 or type II 160. The diene precursor 156 was prepared in turn from 154 via 155, as shown in Scheme 21. Hydrogenation of the C-C double bond in 157 afforded the azepane 158 <2005SL631>. 

Asymmetric hydrogenation of allylic alcohols (14, 39-40).1 Mammalian dol-ichols (2) are terminal dihydropolyisoprenols which are involved in glycoprotein synthesis. They contain one terminal chiral primary allylic alcohol group. The polyprenols 3 present in plants correspond to dolichols except that they lack the terminal double bond considered to be (Z). They can be obtained by hydrogenation of 2 catalyzed by (bistrifluoroacetate)ruthenium(II) and (S)-l, which affects only the terminal double bond to provide (S)-3 in >95% ee. 

Interestingly, when RuCl2(= CHPh)(PCy3)(bis(mesityl)imidazolylidene) was used as the catalyst in dichloromethane under a N2 H2 (95 5) atmosphere, the ring-closing metathesis of allyl homoallyl ethers and to-sylamide was performed but a subsequent ruthenium-catalyzed double bond isomerization took place and very little hydrogenation was observed (Scheme 24) [50]. 

Taking advantage of the slow hydrogenation of carbon-carbon double bonds at room temperature in the presence of platinum dioxide, it was possible to perform the ruthenium-catalyzed cross coupling reaction of electron-deficient olefins such as conjugated enones and acrylic derivatives with allyl silanes in the presence of Pt(>2 under hydrogen (Scheme 46) [99]. Prolonged... 

Among the most significant developments in the field of catalysis in recent years have been the discovery and elucidation of various new, and often novel, catalytic reactions of transition metal ions and coordination compounds 13, 34). Examples of such reactions are the hydrogenation of olefins catalyzed by complexes of ruthenium (36), rhodium (61), cobalt (52), platinum (3, 26, 81), and other metals the hydroformylation of olefins catalyzed by complexes of cobalt or rhodium (Oxo process) (6, 46, 62) the dimerization of ethylene (i, 23) and polymerization of dienes (15, 64, 65) catalyzed by complexes of rhodium double-bond migration in olefins catalyzed by complexes of rhodium (24,42), palladium (42), cobalt (67), platinum (3, 5, 26, 81), and other metals (27) the oxidation of olefins to aldehydes, ketones, and vinyl esters, catalyzed by palladium chloride (Wacker process) (47, 48, 49,... 

Several water-soluble ruthenium complexes, with P = TPPMS, TPPTS, or PTA ligands (cf. Section 2.2.3.2), catalyze the selective reduction of crotonaldehyde, 3-methyl-2-butenal (prenal), and trans-cinnamaldehyde to the corresponding unsaturated alcohols (Scheme 2) [33—36]. Chemical yields are often close to quantitative in reasonable times and the selectivity toward the aUyhc alcohol is very high (> 95%). The selectivity of the reactions is critically influenced by the pH of the aqueous phase [11] as well as by the H2 pressure [37]. The hydrogenation of propionaldehyde, catalyzed by Ru(II)/TPPTS complexes, was dramatically accelerated by the addition of inorganic salts [38], too. In sharp contrast to the Ru(II)-based catalysts, in hydrogenation of unsaturated aldehydes rhodium(I) complexes preferentially promote the reaction of the C=C double bond, although with incomplete selectivity [33, 39]. 

This chapter provides an overview of the current state of the understanding of the mechanism of hydrogenations of double bonds catalyzed by the most commonly used transition metals, rhodium, iridium, and ruthenium. The focus of the review will be on recent computational studies, but older computational work and experimental investigations will be discussed in context. Where appropriate, open questions and mechanistic controversies will be addressed. 

In some cases, ruthenium clusters have been found to catalyze selectively the hydrogenation of a C=0 bond next to a C=C double bond [Eq.( 11), cf.Section III. A (77)] or the hydrogenation of one of two C=0 bonds in a given molecule Thus, acetoacetic diethylamide is hydrogenated in the presence of [H3Ru4(CO),2] selectively in the keto function according to... 

Asymmetric hydrogenation was boosted towards synthetic applications with the preparation of binap 15 by Noyori et al. [55] (Scheme 10). This diphosphine is a good ligand of rhodium, but it was some ruthenium/binap complexes which have found spectacular applications (from 1986 up to now) in asymmetric hydrogenation of many types of unsaturated substrates (C=C or C=0 double bonds). Some examples are listed in Scheme 10. Another important development generated by binap was the isomerization of allylamines into enamines catalyzed by cationic rhodium/binap complexes [57]. This reaction has been applied since 1985 in Japan at the Takasago Company for the synthesis of (-)-menthol (Scheme 10). 

Other catalysts are preferred when selectivity is a problem. Ruthenium and Rh are useful catalysts for selective hydrogenation of the olefinic function in oxygenated compounds, a reaction plagued by hydrogenolysis. Ruthenium dioxide catalyzes the hydrogenation of the otherwise unreactive tetrasubstituted double bond in guaiol, 1, without hydrogenoloysis ... 

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