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Chemical compound From Wikipedia, the free encyclopedia
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 | |
Identifiers | |
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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 |
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) | |
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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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]
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]
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.
This methodology was utilized in the total synthesis of (-)-leucomidine B from an enantioenriched monoacid synthesized via a Hf(OTf)4 catalyzed thioacetalization.[9]
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]
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