Amido-ruthenium complex catalysts

Noyori and coworkers reported well-defined ruthenium(II) catalyst systems of the type RuH( 76-arene)(NH2CHPhCHPhNTs) for the asymmetric transfer hydrogenation of ketones and imines [94]. These also act via an outer-sphere hydride transfer mechanism shown in Scheme 3.12. The hydride transfer from ruthenium and proton transfer from the amino group to the C=0 bond of a ketone or C=N bond of an imine produces the alcohol or amine product, respectively. The amido complex that is produced is unreactive to H2 (except at high pressures), but readily reacts with iPrOH or formate to regenerate the hydride catalyst. 

Ruthenium An amido ruthenium(II) complex catalyzes the addition of primary and secondary alcohols to acrylonitrile, crotononitrile, methacrylonitrile, and other unsaturated nitriles at ambient temperature and a low catalyst loading of 0.1 mol% (Scheme 16) [89]. NMR experiments indicate that the basic amido ligand at ruthenium deprotonates the alcohol to give a cationic amido complex [(MeCONH2) RuH(CO)(PCy3)2(5)] (S - nitrile substrate). The authors assume that the nitrile substrate is activated by coordination to ruthenium via the nitrile unit and then attacked by external alkoxide [89]. 

Ruthenium amido complexes (137) effected asymmetric Michael addition of /S-keto esters (134) to cyclopent-2-en-l-one (135) to give quantitatively the corresponding Michael adducts (136) with excellent enantioselectivity (<97% ee), although with a 1 1 diastereoisomer ratio (Scheme 8). The stereochemical outcome of the reaction was significantly influenced by the structure of the catalysts (137) and /S-keto esters.170... 

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