Bis(oxazoline)titanium complexes as chiral catalysts for enantioselective hydrosilylation of ketones - A combined experimental and theoretical investigation

A combined experimental and theoretical investigation has been carried out on a new catalytic system, based on his(oxazoline) (BOX) complexes of titanium. These catalytic species are able to reduce aromatic ketones with good enantiomeric excesses and satisfactory yields. The experimental and the computational (DFT) evidence has provided useful information on the nature of the active catalytic species and on the mechanism of the reaction. The most likely reaction path involves a Ti-IV catalytic species. This result agrees with experimentally obtained evidence that seems to rule out the presence of Ti-III. species. The analysis of the structure of the transition state corresponding to the reduction process (the addition of the hydride to the carbonyl system), provides an interesting insight on the enantioselectivity that characterizes this reaction. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).