Ruthenium amido complexes

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... 

CATALYTIC ENANTIOSELECTIVE MICHAEL REACTION CATALYSED BY WELL-DEFINED CHIRAL RUTHENIUM-AMIDO COMPLEXES... 

Schlenk type filtration apparatus (used to separate the dichloromethane solution of the ruthenium-amido complex from calcium hydride and calcium hydroxide using a filter paper under an argon (or nitrogen) atmosphere)... 

A highly practical asymmetric Michael reaction catalysed by the chiral ruthenium-amido complex with a M/NH bifunction has been developed.19,141 A variety of... 

Density functional theory calculations have led to the proposed mechanism shown in Scheme 12.2. A base-generated ruthenium amido complex activates H2 to afford a ruthenium amine hydride intermediate. In the rate-determining step, transfer of a Ru—H/N—H pair in the outer sphere yields a hemiacetal complex, which degrades via ruthenium-induced C—O cleavage and proton transfer from OH to NH to yield alcohol and aldehyde the latter undergoes outer-sphere reduction to alcohol. 

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. 

Reaction of the ruthenium(II) amido complex [Ru (NHPh)(Tp)(CO)(PPh3)l with two equivalents of AgOTf in the presence of excess NEts or lutidine generates [Ru qNHPh)(Tp)(CO)-(PPh3)](OTf)2 (115d). The BAr 4 (AT = C6H3(CF3)2-3,5) salt was also prepared. ... 

The similar ruthenium(II) complex, [Ru(S( — )-PhEtbpy)3]2+ ((S( — )-PhEtbpy = 4,4 -bis[(S)-( — )-l-phenylethylaminocarbonyl]-2,2 -bipyridine), was synthesized by the same authors [27]. In this complex, chiral phenethylamine is introduced into 2,2 -bipyridine through the amido bridge (see Scheme 8C). This complex was also applied to stereoselective photoreduction of Co(acac)3. In this reaction, the stereoselectivity is reverse to that observed in the reaction by [Ru(( — )-men-... 

The ruthenium-catalyzed reduction of polar bonds using H gas, rather than a sacrificial reductant such as isopropanol, is an atom-economical reaction that has been thoroughly explored. A key discovery by our laboratory was that neutral, stmctur-ally characterized metal-amido complexes such as 11 (Scheme 7) could cleave H heterolytically to yield the fran -dihydride complex 12, and that these are crucial intermediates during catalysis.R - Once the H-N-Ru-H moiety is in place, proton and hydride can then be transferred to the substrate. Having methyl groups instead of hydrogens on carbons alpha to the amido group (beta to the ruthenium) in this case and in the case of 1 (Scheme 4) was important to allow the isolation of an amido... 

Scheme 7 Reaction of ruthenium hydrido-amido complex 11 with hydrogen to give the dihydride 12 during ketone hydrogenation...

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]. 

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