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Hafnium(IV) triflate
Names
	IUPAC names Hafnium(IV) trifluoromethanesulfonate;
Identifiers
CAS Number	161337-67-3 ;
3D model (JSmol)	Interactive image;
ChemSpider	21170913;
EC Number	624-948-5;
PubChem CID	9853707;
CompTox Dashboard (EPA)	DTXSID201336882 ;
	InChI InChI=1S/4CHF3O3S.Hf/c42-1(3,4)8(5,6)7;/h4(H,5,6,7);/q;;;;+4/p-4 Key: BQYMOILRPDTPPJ-UHFFFAOYSA-J;
	SMILES 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
Chemical formula	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:
Pictograms
Signal word	Danger
Hazard statements	H314, H315, H319, H335
Precautionary statements	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	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). verify (what is ?) Infobox references

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]

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

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]

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]

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]