Transmetalated

Transmetalation is a chemical process in which ligands or groups move from one metal center to another. When such a transfer occurs, the resulting species that bears the newly attached group is described as transmetalated relative to the starting complex. Transmetalation is a central step in many organometallic-catalyzed transformations, especially cross-coupling reactions, where an organometallic fragment is transferred to a catalytic metal center.

In palladium-catalyzed cross-couplings such as Suzuki–Miyaura, Negishi, Stille, and Kumada-type reactions, a typical cycle involves oxidative addition of an electrophile to palladium, followed by transmetalation in which an organic fragment from a donor metal is transferred to palladium. The transmetalated palladium complex then undergoes reductive elimination to form the coupled product. Other metals participate as donors in transmetalation steps, including platinum, copper, nickel, zinc, tin, boron, and silicon reagents. The thermodynamics and kinetics of transmetalation depend on the relative affinity of the transferring fragment for the donor vs. acceptor metal, as well as the ligand environment, oxidation states, solvent, and bases present.

Transmetalated intermediates can be brief and are frequently probed by spectroscopic methods and computational studies to elucidate mechanism. Side reactions, aggregation, or competing transmetallation can influence the efficiency and selectivity of catalytic cycles.

In summary, transmetalated describes a state in which a fragment has moved from one metal center to another, a transition that underpins many modern catalytic processes and strategies in organic synthesis.