Photo-Assisted Hydrogen Transfer from Alcohol to Limonene Catalyzed by [Rh6(CO)16]

Partial hydrogenation of the exo-olefinic bond in limonene to carvomenthene proceeds smoothly by photocatalytic hydrogen transfer from 2-propanol using [Rh6(CO)16] as a catalyst under UV-irradiation in the presence of acetone. Hydrogen gas evolves after the formation of carvomenthene has been completed. 1-Hydroxy-1-methylethyl radical formed in the reaction of photochemically excited acetone with 2-propanol serves both as an activator for the catalyst and as a hydrogen source.