D. A. Evans Diastereoselective Hydrogenation: Introduction-2 Chem 206 The first rational attempt to identify those FGs which will direct the reaction Cationic Hydrogenation Catalysts H2, 5% Pd-C 10 cis: trans R. Crabtree CH,OH JAm.Chem.Soc.91.2816(1969) J Organomet Chem. 168, 183(1979) CooNa COOMe 53558540 COMe CONH 16e H. Thompson Co-workers, J Am. Chem. Soc. 95, 838 (1973) Rh(+l): d8 The first rational attempt to associate catalyst with substrate: Mechanism of Hydrogenation Cationic Rhodium-() Catalysts S= solvent 50°,c6H6Meo Reductive eliminated CH3 CH3 Oxidative Addition Rxn Catalytic in Rh(4 mol%) Php Thompson& Coworkers, J Am. Chem. Soc. 97, 6232(1974)Rh S S Ph2P S Rh PPh2 S Ph2P PPh2 H Rh S Ph2P PPh2 H Rh H S Ph2P PPh2 H2C H CH2OK MeO O O R CH3O (Ph3P)3RhCl R CH2OH CHO CN COONa COOH COOMe COMe CONH2 MeO CH2O–Rh(PPh3)3 MeO CH2OH H CH3O R O O H H2 Rh Ph2P PPh2 Rh Ph2P PPh2 S S (+S) CH3–CH3 CH2=CH2 H2 H2 (–S) Ir Py PCy3 H Rh H S S Ph2P PPh2 Oxidative Addition Mechanism of Hydrogenation Cationic Rhodium-(I) Catalysts. 18-e- 16-e– (CH2)n – BF4 Schrock & Osborne, J. Am. Chem. Soc. 91, 2816 (1969) (CH2 )n R. Crabtree J. Organomet. Chem. 168, 183 (1979) – PF6 – BF4 The first rational attempt to identify those FGs which will direct the reaction Cationic Hydrogenation Catalysts H. Thompson & Co-workers, J. Am. Chem. Soc. 95, 838 (1973) 10 H2 , 5% Pd-C cis : trans 95 : 5 93 : 7 75 : 25 55 : 45 18 : 82 15 : 85 14 : 86 10 : 90 The first rational attempt to associate catalyst with substrate: cis : trans >98 : 2 Thompson & Coworkers, J. Am. Chem. Soc. 97, 6232 (1974) H2 100 psi Rxn Catalytic in Rh (4 mol%) 50 °C, C6H6 D. A. Evans Diastereoselective Hydrogenation: Introduction-2 Chem 206 S = solvent S = solvent Reductive Elimination Rh(+I): d8