OPTICALLY-ACTIVE PHENANTHROLINES IN ASYMMETRIC CATALYSIS .4. ENANTIOSELECTIVE HYDROSILYLATION OF ACETOPHENONE BY RHODIUM CHIRAL ALKYL PHENANTHROLINE CATALYSTS

The in situ catalysts prepared from [Rh(Cod)Cl]2 (Cod = 1,5-cyclooctadiene) and chiral alkylphenanthroline ligands 1-6 display a remarkable activity in the asymmetric hydrosilylation of acetophenone affording, after hydrolysis, the expected 1-phenylethanol in high yield and complete selectivity. High enantioselectivities, up to 76%, were obtained in the presence of 2-substituted derivatives 5 and 6, whereas 3-alkylphenanthrolines 1-4 gave e.e.'s not higher than 6%. High chemical yields, but modest enantioselectivities (10-20% e.e.) were recorded with the potentially terdentate ligands 7-10. Chiral alkylphenanthrolines were poorly efficient ligands in the asymmetric Ni-catalysed cross-coupling of -alpha-methylbenzylmagnesium chloride with vinyl bromide.