Hydrogenation of geraniol using ruthenium–BINAP catalysts

Abstract

The asymmetric hydrogenation of geraniol (3,7-dimethylocta-2,6-dien-1-ol) to citronellol was performed using ruthenium BINAP catalysts at 60 °C. The influence of solvent (methanol, ethanol, 1-propanol, and 2-propanol), catalyst type (Ru(OAc)₂(BINAP), R-Ru(OAc)₂(T-BINAP), and R-RuCl[(p-cymene)(BINAP)]Cl), and hydrogen pressure (5–40 bar) was studied. The reaction rate decreased in the order methanol > ethanol > 1-propanol > 2-propanol, but the selectivity and enantiomeric excess were independent of solvent. R-Ru(OAc)₂(T-BINAP) afforded the highest enantiomeric excess of S-citronellol. The reaction rate and enantioselectivity increased with hydrogen pressure. A kinetic model was developed based on the proposed reaction mechanism with subsequent parameter estimation.