M C. White, Chem 153 Hydrogenation -146 Week of october 15. 2002 Schrock-Osborn /Crabtree: Cationic catalysts y3 (PF6) H cis-oxidative ClS-migratory (PF6) PC (PF6) solvated active catalyst Crabtree Acc Chem Res 1979(12)331 Turnover Frequency(ToF) Wilkinsons catalyst ordinatively"unsat benzene/EtOH 25C atonic hydrogenation catalysts Schrock-Osborn catalyst (PF6) weakly coordinating solvents PPh provides the olefin substrate with relatively free access to the metal,s reactive site. These cationic catalysts are also P Crabtree's catalyst (PF6) TOF =mol reduced substrate/mol catalyst/hM.C. White, Chem 153 Hydrogenation -146- Week of October 15, 2002 Schrock- Osborn /Crabtree: Cationic catalysts Diene ligated cationic catalysts mode of activation: Ir(I) PCy3 N (PF6-) Ir(III) PCy3 H (PF6-) H N Ir(III) PCy3 H (PF6-) N + + + S Ir(I) PCy3 N (PF6-) + repeat S Ir(I) S PCy3 N (PF6-) + diene ligated catalyst precursor solvated active catalyst H2 cis-oxidative addition cis-migratory insertion cis-reductive elimination Crabtree Acc Chem Res 1979 (12) 331. Ph3P Rh(I) Ph3P PPh3 Cl Ir(I) N PCy3 (PF6-) Rh(I) PPh3 PPh3 (PF6-) + + Turnover Frequency (TOF) TOF = mol reduced substrate/mol catalyst/h CH2Cl2, 25oC CH2Cl2, 25oC benzene/EtOH, 25oC Schrock-Osborn catalyst Crabtree's catalyst Wilkinson's catalyst 650 4000 6400 700 10 4500 13 ---- 3800 ---- ---- 4000 "Coordinatively" unsaturated cationic hydrogenation catalysts are the most active homogeneous hydrogenation catalysts developed thus far. Use of weakly coordinating solvents provides the olefin substrate with relatively free access to the metal's reactive site. These cationic catalysts are also remarkably selective