Cooperative Catalysis by Iridium Complexes with a Bipyridonate Ligand: Versatile Dehydrogenative Oxidation of Alcohols and Reversible Dehydrogenation-Hydrogenation between 2-Propanol and Acetone

摘要

The oxidation of alcohols to carbonyl compounds is one of the most important and fundamental reactions in organic chemistry. Conventionally, this reaction is carried out by using stoichiometric amounts of harmful oxidants, for example, a chromium reagent. Recently, a number of transition-metal-catalyzed oxidation reactions of alcohols have been developed using environmentally acceptable oxidants, such as molecular oxygen, hydrogen peroxide, or acetone. However, oxidant-free or acceptor-free oxidation based on the catalytic dehydrogenation of alcohols accompanied by the evolution of hydrogen gas must be desirable from the standpoint of atom economy and environmental concerns. Dehydrogenative oxidation of alcohols is important for the production of synthetically useful aldehydes and ketones from readily available alcohols with high atom efficiency, and also for the production of hydrogen gas, which is one of the most promising energy carriers in energy plans for the future.Up to now, various homogeneous catalytic systems have been reported for the dehydrogenative oxidation, of alcohols to carbonyl compounds. Most of these catalytic reactions have to be carried out under reflux in organic solvent at high temperature (> 100°C). Additionally, most of these systems can be utilized only for the oxidation of secondary alcohols, and the systems that effectively oxidize primary alcohols to aldehydes are rare. Currently, there is no catalytic system that is able to dehydrogenatiyely oxidize a wide variety of both primary and secondary alcohols at relatively low temperatures (< 90 °C).