Reactions of Early Transition Metal - Carbon Bonds with N-Heterocycles

Heterocycles are ubiquitous in biological compounds and methods to functionalize them have been of long standing interest. Reactions of early transition metal-carbon bonds with heterocycles are important in two major areas: (1) activation and functionalization of heterocycles and (2) ring-opening of aromatic heterocycles. In the first area, metalcarbon σ bonds determine ortho-metalation and insertion of unsaturated substrates to yield functionalized heterocycles. In the latter area, metal-element multiple bonds become important and provide the driving force for ring-opening reactions. This review will focus on reactions of nitrogen-containing heterocycles. Early transition metals are defined as elements belonging to groups III-V, the lanthanides, and the actinides; the reactivity of complexes featuring the metal in its highest oxidation state (d0fn electron count) and a carbon-based ligand will be described.