A Highly Reusable Carbon-Supported Platinum Catalyst for the Hydrogen- Transfer Reduction of Ketones

摘要

The hydrogen-transfer reduction of organic compounds is an advantageous methodology with respect to catalytic hydroge-nation and other reduction methods for various reasons: a) the hydrogen source is easy to handle (no gas containment or pressure vessels are necessary); b) possible hazards are minimized (molecular hydrogen is a highly flammable, explosive gas); c) the mild reaction conditions used can afford enhanced selectivity; d) catalytic asymmetric transfer hydrogenation can be applied in the presence of chiral ligands. 2-Propanol is the most widely used hydrogen donor since it is cheap, nontoxic, volatile, possesses good solvent properties, and is transformed into acetone, which is environmentally friendly and easy to remove from the reaction system. The transfer hydrogenation of carbonyl compounds has mostly been carried out with 2-propanol as the hydrogen donor, under homogeneous conditions, in the presence of noble-metal complexes. Complexes of the second- or third-row transition metals, such as Ru, Rh, and lr, are the most efficient catalysts devised to date. Among them, ruthenium complexes have been widely studied in homogeneous transfer hydrogenation, especially for the asymmetric reduction of aromatic ketones as well as from a mechanistic point of view. Much less attention has been devoted, however, to the hydrogen-transfer reduction of carbonyl compounds under heterogeneous conditions.