Achiral ruthenium catalyst encapsulated in titanium phosphonate homochiral peptide-based solids for enantioselective hydrogenation of ketones to secondary alcohols

Asymmetric homogeneous catalysis is well established, but the design of new chiral catalysts and the optimization of an existing catalytic system are time- and manpower-exhausting processes. Desirable, heterogeneous, chiral analogues to facilitate catalyst recovery are relatively rare or function poorly. Here we further develop our strategy for facile adaptation of known reactions involving homogeneous achiral catalysts to those involving heterogeneous asymmetric catalysts by use of a homochiral solid scaffold and show the generality of this concept, from hydrolysis and oxidation reactions to hydrogenations. In this case, an inexpensive "off-the shelf" achiral hydrogenation catalyst, Ru^IICl₂(R₂PCH₂CH₂NH) ₂, R = Ph, i-Pr, or t-Bu, embedded within a homochiral matrix is an enantioselective, recyclable heterogeneous catalyst for ketone hydrogenation. The amorphous matrix consists of tripodal poly(phenylglycine) capped with phosphonate moieties and cross-linked with titanium oxide. Hydrogenation of acetophenone derivatives can proceed with high enantioselectivity (up to 95% ee), and catalyst recycling by filtration is very effective.