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.[1]
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| Names | |
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| IUPAC names
Hafnium(IV) trifluoromethanesulfonate
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| Identifiers | |
3D model (JSmol)
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PubChem CID
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CompTox Dashboard (EPA)
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| 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
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irritantant |
| GHS labelling: | |
 
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| 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) | [1] |
| Related compounds | |
Other anions
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Hafnium tetrachloride Hafnium tetrafluoride Hafnium(IV) bromide Hafnium(IV) iodide |
Other cations
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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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Preparation
editThe 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
editElectrophilic Substitutions
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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, 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]
4_alkynes.jpg)
Nucleophilic Substitutions
editIn 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.
This methodology was utilized in the total synthesis of (-)-leucomidine B from an enantioenriched monoacid synthesized via a Hf(OTf)4 catalyzed thioacetalization.[9]
-leucomidine_B.jpg)
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]
References
edit- ^ 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.
- ^ a b 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.
- ^ 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
- ^ Calloway, N. O. (1935-12-01). "The Friedel-Crafts Syntheses". Chemical Reviews. 17 (3): 327–392. doi:10.1021/cr60058a002. ISSN 0009-2665.
- ^ 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.
- ^ 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. S2CID 93455317.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.