M.C. White, Chem 153 Overview -284- Week of november 11. 2002 Hydrogenation via o-bond metatheses: Rulll) catalysts Monohydride identified as active catalyst: Formation of Ru(iv) dihydride is prohibitively high in cat RuCl(PPh3)3 NEt3 (I eql, benzene Ph3PRy(ay"PPh3 H2(1 eq) +¨CI"HNE Et3 H2(l atm), benzene: ethanol, rt H2cO HcO NCOCH3 (R-1(0.5-1mo% OAe EtOH: CH,CI,(5: 1 ), H,(4 atm), 23 OCH3 H3 Possible monmohydride hydrogenation mechanisms(Hydrogenations, pg. 156) LmMX々H,耳 H、H a-bond metathesis no oxidation state C-bond metathesis B LmH_LmMH—LmM LM ozonolysisM.C. White, Chem 153 Overview -284- Week of November 11, 2002 Hydrogenation via σ-bond metatheses: Ru(II) catalysts Possible monohydride hydrogenation mechanisms (Hydrogenations, pg. 156). L mMn X H2 LnMn X H H L mMn H σ-bond metathesis no oxidation state change R L mMn L m Mn H H H R R σ-bond metathesis L mMn HX H H L mMn H2 base-promoted heterolytic cleavage B L mMn H HB L mMn H R L mMn R HB L mMn H R L mMn protonolysis Ph3P Ru(II) PPh3 PPh3 H Cl RuCl2(PPh3)3 H2 (1 eq) NEt3 (1 eq), benzene + -Cl +HNEt3 cat. H2 (1 atm), benzene:ethanol, rt quantitative R R RuCl2(PPh3)2 Monohydride identified as active catalyst: Formation of Ru(IV) dihydride is prohibitively high in energy. Wilkinson's Ru catalyst Noyori's Ru catalyst NCOCH3 H3CO AcO OAc OCH3 P Ph2 Ru(II) Ph2 P O O O O NCOCH3 H3CO AcO OAc OCH3 (0.5-1 mol%) EtOH:CH2Cl2 (5:1), H2 (4 atm), 23o C 92% yield 95% ee (R)-1