N-Heterocyclic Carbene Analogues with Low-Valent Group 13 and Group 14 Elements: Syntheses, Structures, and Reactivities of a New Generation of Multitalented Ligands

The stabilization and isolation of highly reactive species has long been the subject of chemical research. This review will focus on a large and important class of reactive species that has only recently received considerable attention: lowvalence element heterocycles of the group 13 and 14 elements. The availability of lithium boryl complexes as sources of boryl anions has also opened up a new synthetic route to other metal boryl complexes, namely, nucleophilic attack on metal halide complexes, leading to lithium halide elimination. Although in its infancy, the chemistry of nucleophilic five-membered boryl lithium complexes holds much potential in organic and inorganic synthesis. Saying this, the thermal instability and steric bulk of such systems will likely hinder the rapid advancement of their use by a broad range of chemists.