transmetalations

Transmetalation is a process in organometallic and inorganic chemistry in which a ligand or group is transferred from one metal center to another. It is a fundamental step in many catalytic cycles and in the construction of complex molecules, enabling the exchange of substituents between metal atoms within a single complex or between two different metal centers.

In palladium-catalyzed cross-coupling reactions, transmetalation transfers an organic group from a secondary metal reagent to the palladium center. Common families include Suzuki–Miyaura (boron reagents), Stille (tin reagents), Negishi (zinc reagents), and Kumada (Grignard reagents). The general sequence involves oxidative addition of an electrophile to a low-valent metal, followed by transmetalation to incorporate the organic fragment from the donor metal onto the catalytic metal, and then reductive elimination to forge the new carbon–carbon bond. Transmetalation often requires activation such as a base or a bridging halide and can be sensitive to the ligands, solvent, temperature, and oxidation state of the metals.

Transmetalation also occurs in other contexts, including the preparation and modification of heterobimetallic complexes, and in solid-state or catalytic materials where groups are exchanged between different metal centers. In such cases, the transfer may proceed through bridging ligands, halides, hydroxide, or other coordinating species, and it can influence the stability and reactivity of the resulting compounds.

Factors that influence transmetalation include the identity and oxidation states of the metals, the nature of the transferring group, the supporting ligands, and the reaction medium. Understanding transmetalation is essential for predicting reaction outcomes and optimizing selectivity in many organometallic transformations.