Hydrogen transfer from cyclohexanol to aromatic aldehydes catalyzed by heterogenized ruthenium(II) complexes bound to swellable polymer matrices

Aromatic aldehydes can be reduced to corresponding alcohols by hydrogen transfer from cyclohexanol in the presence of Ru(II) complexes bound to swellable polymer matrices. The kinetics of the reaction has been measured between 100 and 140 °C. The process was shown to depend on the structure of aromatic aldehydes, on the concentrations of aldehyde and hydrogen donor, and on the amount of catalyst. The reaction proceeded efficiently in halogenated hydrocarbon solvents. The metal leaching and deactivation of the catalyst was studied. The metal leaching was different for subsequent catalytic runs and it is most pronounced in the first catalytic run. The IR spectra study for the catalyst deactivation showed that catalyst deactivation may be ascribed to the formation of metallic units bound to two carboxylate groups. This problem can be prevented by esterifying the groups. An apparent activation energy, Ea = 22 ± 1 kcal/mol was obtained, which suggests that the catalytic process involves predominantly a chemically controlled reaction. A general reaction mechanism and rate equation have been proposed.