Manganese‐Catalyzed CH Bond Activation and Functionalization, From Mechanism to Applications

Stoichiometric Mn(I) CH activation and functionalization reactions have seen a steady growth over the last 50 years, with particular interest in catalytic breakthroughs seen in the last 10 years. CH bond functionalization can take place in suitably activated unsaturated aromatic/heteroaromatic ring systems, containing a directing group for Mn(I), with activation typically occurring proximal (ortho) to the directing group. A range of Mn(I) carbonyl complexes can be used as precatalysts for a raft of transformations involving cyclomanganted intermediates and appropriate acceptor molecules, which brings about the formation of a plethora of organic and organometallic products. One of the limitations in Mn(I) carbonyl catalysis is the requirement for typically high catalyst loadings (10 mol% being common). Thus we have focused on mechanistic work that might help solve this problem, particularly if the promising reported synthetic chemistry of Mn(I) carbonyls is to be used more widely, particularly in industry. Finally, we showcase how time-resolved IR spectroscopic methods are particularly useful for probing the mechanistic steps involved in CH bond activation catalysis, from picosecond to second timescale. The approaches used might be amenable to the study of other metal-catalyzed processes.