Diastereoselection and the Influence of Chiraphos on Metal-Centered Chirality in Cis Oxidative Addition of Hydrogen and Triphenylsilane.
ROCHESTER UNIV NY DEPT OF CHEMISTRY
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The complex IrBrCOchiraphos, chiraphos 25,35-bis-diphenylphosphinobutane, has been prepared, and its oxidative addition reactions with H2 and Ph3SiH have been studied. The reaction with H2 proceeds under kinetic control forming an initial pair of diastereomers in a 21 ratio followed by isomerization to a second, more stable pair of diastereomers which commence to form in a2.41 ratio but exist at equilibrium in a 1.31 ratio. The kinetic differentiation observed for each pair of diastereomers results from the influence of chiraphos on the developing chirality at the metal center as the cis oxidative addition proceeds. A reaction coordinate diagram for the system is developed based on the observed kinetic and thermodynamic differentiations of the diastereomers. The oxidative addition of Ph3SiH also takes place under kinetic control followed by isomerization. A 121 kinetic differentiation in the formation of the stable silyl hydride diastereomers occurs at 25 C due solely to the presence of chiraphos.
- Organic Chemistry
- Physical Chemistry