Optically active phenanthrolines in asymmetric catalysis. IV. Enantioselective hydrosilylation of acetophenone by rhodium/chiral alkyl phenanthroline catalysts.

Thein situ catalysts prepared from [Rh(Cod)Cl]2 (Cod = 1,5-cyclooctadiene) and chiral alkylphenanthroline ligands1–6 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 derivatives5 and6, whereas 3-alkylphenanthrolines1–4 gave e.e.'s not higher than 6%. High chemical yields, but modest enantioselectivities (10–20% e.e.) were recorded with the potentially terdentate ligands7–10. Chiral alkylphenanthrolines were poorly efficient ligands in the asymmetric Ni-catalysed cross-coupling of α-methylbenzylmagnesium chloride with vinyl bromide.