Ruthenium complex catalysts product distribution

The water-soluble Ru(II) complex [Ru(i76-C6H6)(CH3CN)3](BF4)2 catalyzed the biphasic hydrogenation of alkenes and ketones with retention of the catalyst in the aqueous phase (87). However, the ruthenium complex moved to the organic phase when benzaldehyde was hydrogenated. In a benzene-D20 system, H-D exchange was observed between H2 and D20. Both monohydridic pathway and a dihydridic pathway are possible for hydrogen activation, and these two different catalytic cycles influence the yield and product distribution. 

Carbon monoxide is hydrogenated over ruthenium zeolites in both methanation and Fischer-Tropsch conditions. is exchanged in the zeolite as the amine complex. The zeolites used are Linde A, X, Y, and L, natural chabazitey and synthetic mordenite from Norton. The zeolites as a support for ruthenium were compared with alumina. The influence of the nature of the zeolite, the ruthenium metal dispersion and the reaction conditions upon activity and product distribution were investigated. These zeolites are stable methanation catalysts and under the conditions used show a narrow product distribution. The zeolites are less active than other supports. Sintering of ruthenium metal in the zeolite supercages shows only minor effects on methanation activity, although under our Fischer-Tropsch conditions more C2 and C3 are formed. 

Tandem GM-RGM (see Scheme 20) can be employed for the synthesis of complex ring systems from simple starting materials. A very noteworthy example of this reaction serves as the cornerstone for the total synthethis of the natural product cyclindrocyclophane. The GM-RGM reaction of diene 182 was completely selective for formation of the head-to-tail isomer 183. The selectivity was attributed to thermodynamic control the head-to-head dimer 184 is considerably less stable. In an effort to synthesize pyrenophorin derivatives, the formation of cyclic dimers (e.g., 186) and trimers (e.g., 187) from treatment of acrylate ester-alkene derivatives (e.g., 185) with various ruthenium metathesis catalysts was examined.The product distribution was very time and concentration dependent higher concentrations favor the trimer over the dimer. 

Hydrogenation of olefins catalyzed by transition metal complexes dissolved in ionic liquid solvents have been reported using rhodium-, and ruthenium- and cobalt-containing catalysts. In these studies it was shown that hydrogenation rates where up to five times higher than the comparable reactions when carried out in propanone. The solubilities of the alkene reagents, TOFs, and product distributions where all strongly influenced by the nature of the anion in the ionic liquid solvent... 

This finding is the consequence of the distribution of various ruthenium(II) hydrides in aqueous solutions as a function of pH [RuHCl(mtppms)3] is stable in acidic solutions, while under basic conditions the dominant species is [RuH2(mtppms)4] [10, 11]. A similar distribution of the Ru(II) hydrido-species as a function of the pH was observed with complexes of the related p-monosulfo-nated triphenylphosphine, ptpprns, too [116]. Nevertheless, the picture is even more complicated, since the unsaturated alcohol saturated aldehyde ratio depends also on the hydrogen pressure, and selective formation of the allylic alcohol product can be observed in acidic solutions (e.g., at pH 3) at elevated pressures of H2 (10-40 bar [117, 120]). (The effects of pH on the reaction rate of C = 0 hydrogenation were also studied in detail with the [IrCp (H20)3]2+ and [RuCpH(pta)2] catalyst precursors [118, 128].)... 

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