Hafnium trifluoromethanesulfonate

Hafnium(IV) triflate or hafnium trifluoromethansulfonate is an inorganic substance with the idealized 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.[1]

Hafnium(IV) Triflate
Names
IUPAC names
Hafnium(IV) trifluoromethanesulfonate
Identifiers
3D model (JSmol)
ChemSpider
EC Number
  • 624-948-5
  • InChI=1S/4CHF3O3S.Hf/c4*2-1(3,4)8(5,6)7;/h4*(H,5,6,7);/q;;;;+4/p-4
    Key: BQYMOILRPDTPPJ-UHFFFAOYSA-J
  • C(F)(F)(F)S(=O)(=O)[O-].C(F)(F)(F)S(=O)(=O)[O-].C(F)(F)(F)S(=O)(=O)[O-].C(F)(F)(F)S(=O)(=O)[O-].[Hf+4]
Properties
Hf(OTf)4
Molar mass 774.8 g/mol
Appearance Colourless solid
Melting point 350 °C (662 °F; 623 K)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 irritantant
GHS labelling:
GHS05: CorrosiveGHS07: Exclamation mark
Danger
H314, H315, H319, H335
P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
Flash point Non-flammable
Safety data sheet (SDS)
Related compounds
Other anions
 Hafnium tetrachloride
Hafnium tetrafluoride
Hafnium(IV) bromide
Hafnium(IV) iodide
Other cations
 Titanium(IV) triflate
Zirconium(IV) triflate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Preparation

The compound was first synthesized by the Kobayashi group in 1995 via the reaction of HfCl4 and triflic acid.[2] This solid is air stable, easy to handle, and commercially available.[3]

Uses

Electrophilic Substitutions
Hf(OTf)4 catalyzed Friedel-Craft acylation and alkylation reactions

Friedel-Craft acylation or alkylation reactions are some of the most important synthetic methodologies to introduce carbonyl or alkyl groups onto aromatic compounds.[4] The first Hf(OTf)4 catalyzed Friedel-Crafts acylation was developed by Kobayashi et al. in 1995.[2][5] The authors demonstrated that Friedel-Crafts acylation could be achieved in excellent yield between arenes and acid anhydrides when utilizing Hf(OTf)4 as a catalyst. Hf(OTf)4, was the most effective in comparison to other Lewis acids including BF3 • OEt2, Sc(OTf)3, and Zr(OTf)4. Similalrly, Hf(OTf)4 shows excellent activity in Friedel-Crafts alkylation’s, and enabled the alkylation of benzene with benzylic and tertiary alkyl chlorides.

Hf(OTf)4-catalyzed Friedel-Crafts alkylation has been utilized in the total synthesis of the altertoxin III framework. This approach provided a more efficient synthesis of the fused-ring structure compared to previous methods.[6]

Hf(OTf)4 mediated synthesis of altertoxins

Hf(OTf)4, alongside Sc(OTf)3 and In(OTf)3, has been shown to activate alkynes and enable electrophilic substitution. In 2004 Song and Lee et al. reported Hf(OTf)4-catalyzed Friedel-Crafts alkenylation of benzene with alkenyl derivatives.[7]

Hf(OTf)4 enabled electrophilic substitution of alkynes

Nucleophilic Substitutions

In 2008, Zhu et al. demonstrated that Hf(OTf)4 was an effective catalyst for the thioacetalization of aldehydes and ketones.[8] In the absence of Lewis acid this reaction can occur in glycerol at 90 °C. Hf(OTf)4 accelerated the reaction rate under milder conditions with only 0.1 mol% catalyst loading. For example, Hf(OTf)4 catalyzes the reaction between benzaldehyde and 2.0 equiv. of either ethanethiol or 1.0 equiv. of propane-1,3,-dithiol readily in quantitative yield.

Hf(OTf)4 catalyzed thioacetalization of benzaldehyde

This methodology was utilized in the total synthesis of (-)-leucomidine B from an enantioenriched monoacid synthesized via a Hf(OTf)4 catalyzed thioacetalization.[9]

Total synthesis of (-)-leucomidine B

In 2009, Nakamura et al. demonstrated that Hf(OTf)4 was uniquely able to catalyzed a Prins reaction between an aryl aldehyde and an O-protected/unprotected cyclohex-3-ene-1,2-dimethanol.[10]

Hf(OTf)4 catalyzed Prins cyclization

References
  1. Ishitani, Haruro; Suzuki, Hirotsugu; Saito, Yuki; Yamashita, Yasuhiro; Kobayashi, Shū (2015). "Hafnium Trifluoromethanesulfonate [Hf(OTf)4] as a Unique Lewis Acid in Organic Synthesis". European Journal of Organic Chemistry. 2015 (25): 5485–5499. doi:10.1002/ejoc.201500423. ISSN 1099-0690.
  2. Hachiya, Iwao; Moriwaki, Mitsuhiro; Kobayashi, Shu (1995-07-01). "Hafnium(IV) Trifluoromethanesulfonate, An Efficient Catalyst for the Friedel–Crafts Acylation and Alkylation Reactions". Bulletin of the Chemical Society of Japan. 68 (7): 2053–2060. doi:10.1246/bcsj.68.2053. ISSN 0009-2673.
  3. Li, Zhiya; Plancq, Baptiste; Ollevier, Thierry (2011), "Hafnium(IV) Trifluoromethanesulfonate", Encyclopedia of Reagents for Organic Synthesis, American Cancer Society, doi:10.1002/047084289x.rn01315, ISBN 978-0-470-84289-8, retrieved 2021-06-12
  4. Calloway, N. O. (1935-12-01). "The Friedel-Crafts Syntheses". Chemical Reviews. 17 (3): 327–392. doi:10.1021/cr60058a002. ISSN 0009-2665.
  5. Hachiya, Iwao; Moriwaki, Mitsuhiro; Kobayashi, Shu (1995-01-16). "Catalytic Friedel-Crafts acylation reactions using hafnium triflate as a catalyst in lithium perchlorate-nitromethane". Tetrahedron Letters. 36 (3): 409–412. doi:10.1016/0040-4039(94)02221-V. ISSN 0040-4039.
  6. Geiseler, Oliver; Müller, Monika; Podlech, Joachim (2013-05-06). "Synthesis of the altertoxin III framework". Tetrahedron. 69 (18): 3683–3689. doi:10.1016/j.tet.2013.03.013. ISSN 0040-4020.
  7. Song, Choong Eui; Jung, Da-un; Choung, Su Yhen; Roh, Eun Joo; Lee, Sang-gi (2004). "Dramatic Enhancement of Catalytic Activity in an Ionic Liquid: Highly Practical Friedel–Crafts Alkenylation of Arenes with Alkynes Catalyzed by Metal Triflates". Angewandte Chemie International Edition. 43 (45): 6183–6185. doi:10.1002/anie.200460292. ISSN 1521-3773. PMID 15549737.
  8. Wu, Yan-Chao; Zhu, Jieping (2008-12-05). "Hafnium Trifluoromethanesulfonate (Hafnium Triflate) as a Highly Efficient Catalyst for Chemoselective Thioacetalization and Transthioacetalization of Carbonyl Compounds". The Journal of Organic Chemistry. 73 (23): 9522–9524. doi:10.1021/jo8021988. ISSN 0022-3263. PMID 18991383.
  9. Gualtierotti, Jean-Baptiste; Pasche, Delphine; Wang, Qian; Zhu, Jieping (2014). "Phosphoric Acid Catalyzed Desymmetrization of Bicyclic Bislactones Bearing an All-Carbon Stereogenic Center: Total Syntheses of (−)-Rhazinilam and (−)-Leucomidine B". Angewandte Chemie International Edition. 53 (37): 9926–9930. doi:10.1002/anie.201405842. ISSN 1521-3773. PMID 25048385.
  10. Nakamura, Masayuki; Niiyama, Kenji; Yamakawa, Takeru (2009-11-25). "Versatile method for the synthesis of 4-substituted 6-methyl-3-oxabicyclo[3.3.1]non-6-ene-1-methanol derivatives: Prins-type cyclization reaction catalyzed by hafnium triflate". Tetrahedron Letters. 50 (47): 6462–6465. doi:10.1016/j.tetlet.2009.08.120. ISSN 0040-4039.
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