Transmetalation
Transmetalation (alt. spelling: transmetallation) is a general chemical reaction type in organometallic chemistry describing the exchange of ligands between two metal centers.
The metal centers need not be the same. The ligands R and R' can be organic or inorganic. The double displacement reaction is conceptually related. Transmetalation is important in the synthesis of various organometallic compounds.
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[edit] Synthesis of Grignard reagents
Using transmetalation, unusual Grignard reagents can be prepared from commercially available isopropylmagnesium bromide. In this way, problems with slow initiation of the Grignard reagent are avoided and precious halides are used more efficiently. Since transmetalation occurs under conditions that tolerate diverse functional groups, this approach expands the utility of the Grignard reaction:[1]
- i-PrMgBr + IC6H4-4-CO2Me → BrMgC6H4-4-CO2Me + i-PrI
[edit] Synthesis of NHC's by transmetalation
Silver N-heterocyclic carbene complexes are easily formed from stable precursors such as imidazolium salts. Once formed, the Ag-NHC reagent can be used to transfer the carbene ligands to other metals containing labile ligands such as acetonitrile or 1,5-cyclooctadiene.[2] Where L-H+ denotes the ligand precursor:
[edit] Use in cross-coupling
Transmetalation appears frequently in the catalytic cycle of various metal-catalysed organic reactions, such as the Stille reaction and the Negishi coupling.
[edit] References
- ^ Paul Knochel, Wolfgang Dohle, Nina Gommermann, Florian F. Kneisel, Felix Kopp, Tobias Korn, Ioannis Sapountzis, Viet Anh Vu "Highly Functionalized Organomagnesium Reagents Prepared through Halogen–Metal Exchange" Angew. Chem. Int. Ed. Engl. 2003, vol. 42, pp. 4302–4320. doi:10.1002/anie.200300579
- ^ Wang, H. M. J., Lin, I. J. B. (1998). "Facile Synthesis of Silver(I)-Carbene Complexes. Useful Carbene Transfer Agents". Organometallics 17 (5): 972–975. doi:10.1021/om9709704.
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