M.C. White, Chem 153 Hydrogenation -147- Week of october 15. 2002 Cationic catalysts: substrate-directed hydrogenations -J3 2.5mo% CH,Ch, H,(I atm),rt The availability of a second"open"coordination 98% site on the catalyst now makes it possible to bind a Pd/C(EtOH), 1: 5 (sterics) ligating group on the substrate in addition to the lefin. This "two-point"binding has important Py mplications on the selectivity of product formation (PF6) The ability of a late metal complex to effectively bind hard functionality(hydroxyls, ketones, etc.) is attributed to the lewis acidic properties impa on the complex by the overall positive charge Crabtree JOC 1986(51)2655 Other functionalities with lewis basic sites also direct Esters: above abore above d/C1.35:1 (±) PdC1.26:1 Pd/C 1:4 For a comprehensive review of cyclic and acyclic ubstrate- directed hydrogenations see: Hoveyda 0 Evans, and Fu Chem. Rev. 1993(93)1307 and >99:1 D.A. Evans. Chem 206 notes Pd/C 1: 9(steric approach control)M.C. White, Chem 153 Hydrogenation -147- Week of October 15, 2002 Cationic catalysts: substrate-directed hydrogenations CH2Cl2, H2 (1 atm), rt Me OH Ir(I) PCy3 N (PF6-) + 2.5 mol% Me OH H i-Pr OH Me H Ir(III) Cy3P Py (PF6-) H + Me OH H 98% 64:1 Pd/C (EtOH), 1:5 (sterics) Crabtree JOC 1986 (51) 2655. The availability of a second "open" coordination site on the catalyst now makes it possible to bind a ligating group on the substrate in addition to the olefin. This "two-point" binding has important implications on the selectivity of product formation. The ability of a late metal complex to effectively bind hard functionality (hydroxyls, ketones, etc...) is attributed to the lewis acidic properties imparted on the complex by the overall positive charge. Other functionalities with lewis basic sites also direct: CO2Me Me H CO2Me Me Me O Me O Me Me H O Me Me O Me Me H Esters: 56:1 Pd/C 1.35:1 above 124:1 Pd/C 1.26:1 above Ketones: 97% >99% 999:1 Pd/C 1:4 above >99% Ethers N H N O O N H N O O Me above >99:1 Pd/C 1:9 (steric approach control) H Amides: 5 mol% (±) (±) (±) For a comprehensive review of cyclic and acyclic substrate-directed hydrogenations see: Hoveyda, Evans, and Fu Chem. Rev. 1993 (93) 1307 and D.A. Evans; Chem 206 notes