Rh(I)-Catalyzed Cycloisomerization of 1,6-Enynes

Catalytic addition of C-H bonds across C-C unsaturated systems promoted by iridium(i) and its group IX congeners

Transition metal-catalyzed hydrocarbonations of unsaturated substrates have emerged as powerful synthetic tools for increasing molecular complexity in an atom-economical manner. Although this field was traditionally dominated by low valent rhodium and ruthenium catalysts, in recent years, there have been many reports based on the use of iridium complexes. In many cases, these reactions have a different course from those of their rhodium homologs, and even allow performing otherwise inviable transformations. In this review we aim to provide an informative journey, from the early pioneering examples in the field, most of them based on other metals than iridium, to the most recent transformations catalyzed by designed Ir(i) complexes. The review is organized by the type of C-H bond that is activated (with C sp², sp or sp³), as well as by the C-C unsaturated partner that is used as a hydrocarbonation partner (alkyne, allene or alkene). Importantly, we discuss the mechanistic foundations of the methods highlighting the differences from those previously proposed for processes catalyzed by related metals, particularly those of the same group (Co and Rh).