Reoxidation of Transition‐metal Catalysts with O2

Abstract

Transition‐metal catalyzed oxidation reactions are central components of organic chemistry. On behalf of green and sustainable chemistry, molecular oxygen (O2) has been considered as an ideal oxidant due to its natural, inexpensive, and environmentally friendly characters, and therefore offers attractive academic and industrial prospects. In recent years, some powerful organic oxidation methods have been continuously developed. Among them, the use of molecular oxygen (O2) as a green and sustainable oxidant has attracted considerable attentions. However, the development of new transition metal‐catalyzed protocols using O2 as an ideal oxidant is highly desirable but very challenging because of the low standard electrode potential of O2 to reoxidize the transition‐metal catalysts. In this Account, we highlight some of our progress toward the use of transition‐metal catalyzed aerobic oxidation reactions. Through the careful selection of ligand and the acidic additives, we have successfully realized the reoxidation of Cu, Pd, Mn, Fe, Ru, Rh, and bimetallic catalysts under O2 or air atmosphere (1 atm) for the oxidative coupling, oxygenation reactions, oxidative C‐H/C‐C bond cleavage, oxidative annulation, and olefins difunctionalization reactions. Most of the reactions can tolerate a range of functional groups. These methods provide new strategies for the green synthesis of alkynes, (α‐keto)amides/esters, ketones/diones, O/N‐heterocycles, β‐azido alcohols, and nitriles. The high efficiency, low cost, and simple operation under air make these methodologies very attractive and practical. We will also discuss the mechanisms of these reactions which might be useful to promote the new type of aerobic oxidative reaction design.