Nickelacyclobutanes: Versatile Reactivity and Role as Catalytic Intermediates

Metallacyclobutanes are intermediates in several catalytic cycles such as olefin metathesis and cyclopropanation. Furthermore, nickel is attracting attention as a versatile, earth-abundant metal in developing new homogeneous catalytic transformations. In this context, the current literature on nickelacyclobutanes and their role in catalysis is reviewed. First, catalytic reactions involving a (putative) nickelacyclobutane intermediate are discussed, including cyclopropanations and various transformations of methylenecyclopropane. Second, studies of the stoichiometric reactivity of nickelacyclobutanes relying on their direct observation or even isolation are detailed. In particular, the relationship between the structure of nickelacyclobutanes and their reactivity is highlighted. Finally, future prospects for the development of new catalytic transformations relying on nickelacyclobutane intermediates are briefly outlined.