transmetallating

Transmetallation, or the transmetallating step, is the transfer of a ligand or organic group from one metal center to another within a single compound or between two metal-containing species. It is a key step in many organometallic reactions and catalytic cycles, enabling the relocation of an organic fragment between metals without breaking all bonds to carbon.

In cross-coupling chemistry, transmetallation transfers the organic group from a metal bound to one reagent (such as boron, zinc, tin, or silicon) to a palladium, nickel, or another transition-metal center. Notable families include Negishi (organozinc reagents to Pd or Ni), Kumada (Grignard reagents to transition metals), Stille (organo­tin to Pd), and Suzuki–Miyaura (organoboron to Pd).

Mechanistically, transmetallation often involves dinuclear intermediates or bridged halide species, with exchange of the organic fragment from one metal to another. It can proceed via SN2-like processes or through four-centered transfer pathways. The rate and outcome are influenced by the metals involved, the ligands and oxidation states, the nature of the halide or leaving group, the base or solvent, and the overall catalytic context.

Significance and scope: transmetallation is central to many catalytic cycles that form C–C bonds, making possible the use of stable organometallic reagents as carbon sources. It is widely encountered in synthesis, materials chemistry, and industrial processes that rely on cross-coupling and related transformations.