Triflate

Triflate, also known by the systematic name trifluoromethanesulfonate, is a functional group with the formula CF3SO3−. The triflate group is often represented by −OTf, as opposed to −Tf (triflyl). For example, n-butyl triflate can be written as CH3CH2CH2CH2OTf.

Triflate group
Triflate anion

The corresponding triflate anion, CF
3SO−
3, is an extremely stable polyatomic ion; this comes from the fact that triflic acid (CF3SO3H) is a superacid; i.e. it is more acidic than pure sulfuric acid, already one of the strongest acids known.

Applications

A triflate group is an excellent leaving group used in certain organic reactions such as nucleophilic substitution, Suzuki couplings and Heck reactions. Since alkyl triflates are extremely reactive in SN2 reactions, they must be stored in conditions free of nucleophiles (such as water). The anion owes its stability to resonance stabilization which causes the negative charge to be spread over the three oxygen atoms and the sulfur atom. An additional stabilization is achieved by the trifluoromethyl group as a strong electron-withdrawing group.

Triflates have also been applied as ligands for group 11 and 13 metals along with lanthanides.

Lithium triflates are used in some lithium ion batteries as a component of the electrolyte.

A mild triflating reagent is phenyl triflimide or N,N-bis(trifluoromethanesulfonyl)aniline, where the by-product is [CF3SO2N−Ph]−.

Triflate mesomeric stability

Triflate salts

Triflate salts are thermally very stable with melting points up to 350 °C for sodium, boron and silver salts especially in water-free form. They can be obtained directly from triflic acid and the metal hydroxide or metal carbonate in water. Alternatively, they can be obtained from reacting metal chlorides with neat triflic acid or silver triflate, or from reacting barium triflate with metal sulfates in water:[1]

MCln + n HOTf → M(OTf)n + n HCl
MCln + n AgOTf → M(OTf)n + n AgCl ↓
M(SO4)n + n Ba(OTf)2 → M(OTf)2n + n BaSO4 ↓

Metal triflates are used as Lewis acid catalysts in organic chemistry. Especially useful are the lanthanide triflates of the type Ln(OTf)3 (where Ln = lanthanide). A related popular catalyst scandium triflate is used in such reactions as aldol reactions and Diels-Alder reactions. An example is the Mukaiyama aldol addition reaction between benzaldehyde and the silyl enol ether of cyclohexanone with an 81% chemical yield.[2] The corresponding reaction with the yttrium salt fails:

ScOTf3-mediated aldol condensation

Triflate is a commonly used weakly coordinating anion.

Use of Ni(OTf)2 to facilitate C-H functionalization[3]

See also

References
  1. Dixon, N. E.; Lawrance, G. A.; Lay, P. A.; Sargeson, A. M.; Taube, H. (1990). "Trifluoromethanesulfonates and Trifluoromethanesulfonato-O Complexes". Inorganic Syntheses. 28: 70–76. doi:10.1002/9780470132593.ch16.
  2. Kobayashi, S. (1999). "Scandium Triflate in Organic Synthesis". European Journal of Organic Chemistry. 1999 (1): 15–27. doi:10.1002/(SICI)1099-0690(199901)1999:1<15::AID-EJOC15>3.0.CO;2-B.
  3. Aihara, Yoshinori; Chatani, Naoto (2013-04-10). "Nickel-Catalyzed Direct Alkylation of C–H Bonds in Benzamides and Acrylamides with Functionalized Alkyl Halides via Bidentate-Chelation Assistance". Journal of the American Chemical Society. 135 (14): 5308–5311. doi:10.1021/ja401344e. PMID 23495861.
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