Ruthenium-catalyzed hydrogenation unsaturated alcohols

Reduction of unsaturated substrates can also be performed by hydrogen transfer, usually from formate, catalyzed by rhodium and ruthenium complexes. Joo and co-workers have shown that RuCl2(tppms)2 [44] and RuCl2(PTA)4 [45,46] transforms aromatic as well as a, -unsaturated aldehydes to the corresponding aromatic or unsaturated alcohols, with a selectivity up to 98% in the latter case,... 

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]. 

Shibahara F, Bower JF, Krische MJ (2008) Diene hydroacylation from the alcohol or aldehyde oxidation level via ruthenium-catalyzed C-C bond-forming transfer hydrogenation synthesis of p, y-unsaturated ketones. J Am Chem Soc 130 14120-14122... 

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