Triflate

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Triflate group Triflate.png
Triflate group
Triflate anion Triflate-anion.png
Triflate anion

In organic chemistry, triflate (systematic name: trifluoromethanesulfonate), is a functional group with the formula R−OSO2CF3 and structure R−O−S(=O)2−CF3. The triflate group is often represented by −OTf, as opposed to −Tf, which is the triflyl group, R−SO2CF3. For example, n-butyl triflate can be written as CH3CH2CH2CH2OTf.

Contents

The corresponding triflate anion, CF3SO3, 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 symmetrically over the three oxygen atoms. An additional stabilization is achieved by the trifluoromethyl group, which acts as a strong electron-withdrawing group using the sulfur atom as a bridge.

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 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]

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 is a lanthanoid). 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:

Sc(OTf)3-mediated aldol condensation ScOTf3-mediated aldol condensation transp.png
Sc(OTf)3-mediated aldol condensation

Triflate is a commonly used weakly coordinating anion.

Use of
Ni(OTf)2 to facilitate C-H functionalization Ni(OTf)2 scheme.tif
Use of Ni(OTf)2 to facilitate C–H functionalization

See also

Related Research Articles

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<span class="mw-page-title-main">Leaving group</span> Atom(s) which detach from the substrate during a chemical reaction

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<span class="mw-page-title-main">Alkylation</span> Transfer of an alkyl group from one molecule to another

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Scandium trifluoromethanesulfonate, commonly called scandium triflate, is a chemical compound with formula Sc(SO3CF3)3, a salt consisting of scandium cations Sc3+ and triflate SO
3
CF
3
anions.

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Lanthanide triflates are triflate salts of the lanthanides. These salts have been investigated for application in organic synthesis as Lewis acid catalysts. These catalysts function similarly to aluminium chloride or ferric chloride, but they are water-tolerant (stable in water). Commonly written as Ln(OTf)3·(H2O)9 the nine waters are bound to the lanthanide, and the triflates are counteranions, so more accurately lanthanide triflate nonahydrate is written as [Ln(H2O)9](OTf)3.

<span class="mw-page-title-main">Methyl trifluoromethanesulfonate</span> Chemical compound

Methyl trifluoromethanesulfonate, also commonly called methyl triflate and abbreviated MeOTf, is the organic compound with the formula CF3SO2OCH3. It is a colourless liquid which finds use in organic chemistry as a powerful methylating agent. The compound is closely related to methyl fluorosulfonate (FSO2OCH3). Although there has yet to be a reported human fatality, several cases were reported for methyl fluorosulfonate (LC50 (rat, 1 h) = 5 ppm), and methyl triflate is expected to have similar toxicity based on available evidence.

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<span class="mw-page-title-main">Silver trifluoromethanesulfonate</span> Chemical compound

Silver trifluoromethanesulfonate, or silver triflate is the triflate (CF3SO3) salt of Ag+. It is a white or colorless solid that is soluble in water and some organic solvents including, benzene. It is a reagent used in the synthesis of organic and inorganic triflates.

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<span class="mw-page-title-main">Hafnium trifluoromethanesulfonate</span> Chemical compound

Hafnium(IV) triflate or hafnium trifluoromethansulfonate is a salt with the formula Hf(OSO2CF3)4, also written as Hf(OTf)4. Hafnium triflate is used as an impure mixture as a catalyst. Hafnium (IV) has an ionic radius of intermediate range (Al < Ti < Hf < Zr < Sc < Ln) and has an oxophilic hard character typical of group IV metals. This solid is a stronger Lewis acid than its typical precursor hafnium tetrachloride, HfCl4, because of the strong electron-withdrawing nature of the four triflate groups, which makes it a great Lewis acid and has many uses including as a great catalyst at low Lewis acid loadings for electrophilic aromatic substitution and nucleophilic substitution reactions.

<span class="mw-page-title-main">Nitro-Mannich reaction</span>

The nitro-Mannich reaction is the nucleophilic addition of a nitroalkane to an imine, resulting in the formation of a beta-nitroamine. With the reaction involving the addition of an acidic carbon nucleophile to a carbon-heteroatom double bond, the nitro-Mannich reaction is related to some of the most fundamental carbon-carbon bond forming reactions in organic chemistry, including the aldol reaction, Henry reaction and Mannich reaction.

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. ISBN   9780470132593.
  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 (10 April 2013). "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.