Cyclometallation

Cyclometallation is a type of organometallic reaction where a metal atom forms a new bond with a carbon atom of a ligand, and simultaneously forms a new bond with another atom within the same ligand, creating a metallacycle. This process typically involves an initial coordination of the metal to a heteroatom, such as nitrogen, oxygen, or sulfur, followed by a C-H bond activation on an adjacent group. The formation of the metallacycle is often driven by the stability of the resulting ring system.

These reactions are prevalent with transition metals, particularly those in the late transition series like palladium, platinum, rhodium, and iridium, as well as with certain main group metals. The substrates for cyclometallation are usually molecules containing both a coordinating heteroatom and an aromatic or unsaturated moiety capable of undergoing C-H activation.

Cyclometallated complexes find extensive use in catalysis, organic synthesis, and materials science. In catalysis, they can serve as pre-catalysts or active catalytic species for various transformations, including cross-coupling reactions, oxidation, and C-H functionalization. Their unique electronic and structural properties also make them valuable in the development of luminescent materials, such as organic light-emitting diodes (OLEDs), and in medicinal chemistry as potential therapeutic agents. The regioselectivity of cyclometallation is an important aspect, as it dictates which C-H bond is activated and thus the structure of the final metallacycle.