M C. White, Chem 153 Hydrogenation -152 Week of october 15. 2002 Asymmetric Hydrogenation A bidentate, C) symmetric version of the cationic Schrock- sbom catalyst affords extraordinarily high levels of enantioselectivity in the hydrogenation of achiral enamides. This was the first demonstration that a chiral ransition metal complex could effectively transfer chirality to a non-chiral substrate with selectivities that rival ransition metal complex: Monsanto Process for the industrial production of L-DOPA(see Structure an Bonding, pg. 4) (PF6) 1) DIPAMP (common name for Me this bidentate chiral phosphi Schrock-Osborn catalyst COrH COH i-PrOH, H(I atm),rt NHAc NHAc A variety of bidentate chiral phosphines have since been synthesized and used to effect the hydrogenation of aromatic enamides(important substrates for the efficient generation of amino acids H PPh PPh NM PPh) n PPh Chiraphos(99%ee) SKEWPHOS (92%ee) NORPHOS (95%ee) DIOP(85%ee) BPPFA(93%ee) We'll see these ligands again effecting asymmetry in a wide assortment of mechanistically unrelated metal analyzed reactions with prochiral substrates Privileged ligand class": ligands that communicat PPh asymmetry effectively with a transition state PPh2 Fe PPh localized at the metal center, irrespective of the nature of the transition state E.N. Jacobsen R personal communIcation BINAP(100%ee) DuPHOS(99%ee) BICP(97%ee) JOSIPHOS(96%ee) E N Jacobsen. Chem 153 notes. Spring 2001 For review on DuPhos: Burk Acc. Chem. Res. 2000 (33)363.M.C. White, Chem 153 Hydrogenation -152- Week of October 15, 2002 Asymmetric Hydrogenation A variety of bidentate chiral phosphines have since been synthesized and used to effect the hydrogenation of aromatic enamides (important substrates for the efficient generation of amino acids): PPh2 PPh2 Chiraphos (99% ee) PPh2 PPh2 SKEWPHOS (92% ee) PPh2 PPh2 BINAP (100% ee) P P R R R R DuPHOS (99% ee) PPh2 PPh2 NORPHOS (95% ee) H H PPh2 PPh2 BICP (97% ee) O O PPh2 PPh2 H H DIOP (85% ee) Fe PPh2 NMe2 PPh2 BPPFA (93% ee) Fe PPh2 PCy2 PPh2 JOSIPHOS (96% ee) E. N. Jacobsen. Chem 153 notes. Spring 2001. For review on DuPhos: Burk Acc. Chem. Res. 2000 (33) 363. We'll see these ligands again effecting asymmetry in a wide assortment of mechanistically unrelated metal catalyzed reactions with prochiral substrates. "Privileged ligand class": ligands that communicate asymmetry effectively with a transition state localized at the metal center, irrespective of the nature of the transition state. E.N. Jacobsen; personal communication Rh(I) PPh3 PPh3 (PF6-) + Schrock-Osborn catalyst A bidentate, C2 symmetric version of the cationic Schrock-Osborn catalyst affords extraordinarily high levels of enantioselectivity in the hydrogenation of achiral enamides. This was the first demonstration that a chiral transition metal complex could effectively transfer chirality to a non-chiral substrate with selectivities that rival those observed in enzymes. Recall that this led to the 1st commericalized asymmetric process using a chiral transition metal complex: Monsanto Process for the industrial production of L-DOPA (see Structure and Bonding, pg. 4) CO2H NHAc Rh(I) P P (PF6-) + MeO OMe i-PrOH, H2 (1 atm), rt >99% yield CO2H NHAc Knowles JACS 1975 (97) 2567. 93% ee DIPAMP (common name for this bidentate chiral phosphine ligand)