Lanthanide alkylidene and imido complexes

In stark contrast to the transition metals, examples of imido or alkylidene complexes of the lanthanides remain scarce. A recent literature survey reveals that only nine examples of lanthanide imido complexes have been reported, and the majority of these have arisen serendipitously. Concrete examples of species containing lanthanide-carbon multiple bonds are even more sparse. Recently, some rational approaches to the synthesis of lanthanide complexes containing Ln=X functionalities have been detailed (X=C, N). Additionally, a DFT (Density Functional Theory) study of a samarium imido complex has provided insight into the electronic and steric factors that may be necessary to support these unusual reactive groups. This Perspective reviews the work in this field and offers some suggestions to expand this potentially useful class of compounds.