ENANTIOSELECTIVE CATALYSIS .74. LIGAND EXCESS AND INTERMEDIATES IN THE RHODIUM-CATALYZED ENANTIOSELECTIVE HYDROSILYLATION OF ACETOPHENONE WITH PYRIDINEOXAZOLINE LIGANDS

The enantioselective hydrosilylation of acetophenone and diphenylsilane with [Rh(COD)Cl2] and the cocatalysts L1 - L4 was investigated. The substitution of hydrogen in the 6-position of the pyridine ring dramatically reduces the dependence of the optical induction on ligand excess, solvent, and concentration of diphenylsilane, acetophenone, and catalyst. The 6-substituents on the pyridine ring are assumed to block one of the coordination sites of rhodium, preventing further interaction with additional ligands, solvents, substrates, and additives.