Cyclopenta[l]phenanthrenyl and Cyclopenta[a]acenaphthylenyl Half-Sandwich Complexes of Ruthenium as Racemization Catalysts for Secondary Alcohols

Several half-sandwich complexes of ruthenium with cyclopenta[l]phenanthrenyl and cyclopenta[a]acenaphthylenyl ligands containing fused aromatic ring substituents on the cyclopentadienyl ring were prepared and characterized by NMR and X-ray crystallography. Activities of the complexes as racemization catalysts for secondary alcohols were preliminarily screened by using (S)-phenylethanol as the substrate. The catalytic activities of the fused-ring complexes depend strongly on the number of other substituents in the five-membered ring and are inferior to those reported earlier for chlorodicarbonyl(pentaphenylcyclopentadienyl)ruthenium, currently considered as the best catalyst candidate for dynamic kinetic resolution of secondary alcohols by combined enzyme/metal catalysis.