M C. White, Chem 153 Hydrogen -150- Week of october 15. 2002 Mechanism of hydrogenation: bidentate cationic complexes ring strain results in more facile (PF6) PPh Schrock-Osborn type catalyst nbd)(diphos-4) BF4 Halpern's mechanism for cationic Rh() catalysts with bidentate Ph H? Meoh Ph observed by NMR Ph2 observed by NMR bserved by nmr oxidative addition(0A) Insertion Halpern Science 1982(217)401M.C. White, Chem 153 Hydrogenation -150- Week of October 15, 2002 Mechanism of hydrogenation:bidentate cationic complexes Rh(I) PPh3 PPh3 (PF6-) + Schrock-Osborn catalyst Rh(I) Ph2 P P Ph2 (PF6-) + ()n= 3 nbd (norbornadiene) ring strain results in more facile hydrogenation diphos Schrock-Osborn type catalyst most commonly used: [Rh(nbd)(diphos-4)]BF4 Halpern's mechanism for cationic Rh(I) catalysts with bidentate phosphine ligands: Halpern Science 1982 (217) 401. H2 MeOH Ph CO2Me NHAc H2 oxidative addition (OA) RDS (rate determining step) stereospecific cis-migratory insertion stereospecific reductive elimination observed by NMR observed by NMR observed by NMR S Rh(I)S Ph2 P P Ph2 + Rh(I) Ph2 P P Ph2 + NH H Ph O Rh(I) Ph2 P P Ph2 + R NH H Ph H Rh(III) Ph2 P P Ph2 + R H O (R) NH O Rh(III) Ph2 P P Ph2 + H Ph H R H S Ph CO2Me NHAc