M.C. White, Chem 153 Hydrogenation-145- Week of october 15. 2002 wilkinson: directing group effects Phb, 0.04mol% note: when pd/c was used a mixture of cis and trans K+B. 0.04 mol% Meo H2(6.8 atm, 100psi ) benzene, 50C CIs Isomer( exclusIv reaction without the alkoxide is OK attibuted to the steric hinderance of the PPh tri-substituted double bond, which renders it less able to coordinate to the Rh. The protonated alcohol is not a strong enough nucleophile to associatively displace the anionic chloride ligand Base-assisted formation of the alkoxide results in effective displacement of the chloride ligand and trisubstituted thus directs olef leo Thompson JACS 1974(96)6232 Jardine Prog. Inorg. Chem. 1981(28)63M.C. White, Chem 153 Hydrogenation -145- Week of October 15, 2002 Wilkinson: directing group effects MeO OH trisubstituted Ph3P Rh(I) Ph3P PPh3 Cl 0.04 mol% H2 (6.8 atm, 100psi), benzene, 50oC no reaction Ph3P Rh(I) Ph3P PPh3 Cl 0.04 mol% H2 (6.8 atm, 100psi), benzene, 50oC 68% K+ B￾MeO OH H MeO O-K+ trisubstituted H O Rh H PPh3 H PPh3 cis isomer (exclusive) note: when Pd/C was used a mixture of cis and trans isomers resulted Thompson JACS 1974 (96) 6232. Jardine Prog. Inorg. Chem. 1981 (28) 63. The slow reaction without the alkoxide is attibuted to the steric hinderance of the tri-substituted double bond, which renders it less able to coordinate to the Rh. The protonated alcohol is not a strong enough nucleophile to associatively displace the anionic chloride ligand. Base-assisted formation of the alkoxide results in effective displacement of the chloride ligand and thus directs olefin complexation from the same face