Published on Web 06/07/2002
Stable Dialkyl Ether/Poly(Hydrogen Fluoride) Complexes:
Dimethyl Ether/Poly(Hydrogen Fluoride), A New, Convenient,
1a
and Effective Fluorinating Agent
Imre Bucsi, B e´ la T o¨ r o¨ k, Alfonso Iza Marco, Golam Rasul,
G. K. Surya Prakash,* and George A. Olah*
Contribution from the Loker Hydrocarbon Research Institute and Department of Chemistry,
UniVersity of Southern California, UniVersity Park, Los Angeles, California 90089-1661
Received October 22, 2001
Abstract: The preparation, H, 13C, and 19F NMR structural characterization as well as with DFT-based
theoretical calculations of stable dialkyl ether/poly(hydrogen fluoride) complexes are reported. Dimethyl
ether/poly(hydrogen fluoride) (DMEPHF), are stable complexes of particular interest and use. The DFT
calculations, that are in agreement with NMR data, suggest a cyclic poly(hydrogen fluoride) bridged structure
for DMEPHF. The complex, DME-5 HF was found to be a convenient and effective new fluorinating agent
with the ease of workup and applied to several fluorination reactions, such as the hydrofluorination and
bromofluorination of alkenes, and fluorination of alcohols giving good to excellent yield with high selectivity.
1
Homologous dialkyl ether/poly(hydrogen fluoride) (R
suitable for fluorination reactions.
2
O/[HF]n,, R ) Et, nPr) systems are also stable and
widely used in organofluorine chemistry.1
-3
The prepa-
Introduction
ration of the solid poly(vinylpyridine)/poly(hydrogen fluoride)
The rapidly growing number of organofluorine compounds,
especially in materials and pharmaceutical sciences, justifies the
further search for convenient and safe fluorinating reagents.
5,6
(
PVPHF) complex resulted in substantial improvements due
1-3,7
to easy workup, compared to the liquid amine/HF reagents.
Although, these reagents function as suitable forms of HF, some
difficulties of separation, handling and stability still remain.
1
b
Anhydrous hydrogen fluoride (AHF) is the cheapest and most
widely used fluorinating agent. However, due to its volatility,
high reactivity, corrosiveness and toxic nature, the use of AHF
requires special experimental setup and handling. Extensive
efforts have been made to render AHF less toxic, safe and
Stable alkyl ether/poly(hydrogen fluoride) complexes, have
not yet been reported. Despite the fact that HF forms complex
8,9
with several O-containing compounds, these adducts were not
isolated nor characterized or explored as fluorinating reagents.
The only relevant report is the use of HF/tetrahydrofuran (THF)
mixtures and its utilization in polymerization of THF.10
1-3
convenient in handling by developing modified HF reagents.
As a result, effective alternatives were developed, such as our
4
pyridinium/poly(hydrogen fluoride) (PPHF, Olah’s reagent),
5
,6
We now report the preparation of stable dialkyl ether/poly-
(hydrogen fluoride) complexes (R2O/[HF]n, R ) Me, Et, nPr).
The dimethyl ether/poly(hydrogen fluoride) systems, as repre-
sentatives of the broad class of dialkyl ether/poly(hydrogen
fluoride) complexes, were studied in detail. The structural
and poly(vinylpyridinium)/poly(hydrogen fluoride) (PVPHF)
7
complexes and a series of HF/amine complexes. The pyri-
dinium/poly(hydrogen fluoride) (30/70) system was found to
be a versatile fluorinating agent and is used in a wide variety
of fluorination reactions.4 On the basis of the successful
stabilization of HF with pyridine other amines were also
employed. As a result, amine-stabilized HF reagents became
1
13
characterization of the complexes was carried out by H, C,
19
and F NMR spectroscopy. The spectroscopic data and density
functional theory (DFT) calculations indicate preferred cyclic
structure for these complexes. The complexes were found to
be generally applicable, new fluorinating reagents. Their
advantageous use has been illustrated through applications, such
as hydrofluorination and bromofluorination of alkenes and
fluorination of alcohols.
*
To whom correspondence should be addressed. E-mail: olah@usc.edu.
(
1) (a) Considered Synthetic Methods and Reactions, Part. 205. For Part 204,
see: Prakash, G. K. S.; Tongco, E. C.; Matthew, T.; Vankar, Y. D.; Olah,
G. A. J. Fluorine Chem. 2000, 101, 199. (b) Olah, G. A., Chambers, R.
D., Prakash, G. K. S., Eds.; Synthetic Fluorine Chemistry; Wiley: New
York, 1992.
(
(
(
2) Yoneda, N. Tetrahedron 1991, 47, 5329.
3) Hiyama, T., Ed.; Organofluorine Compounds; Springer: Berlin, 2000.
4) Olah, G. A.; Welch, J. T.; Vankar, Y. D.; Nojima, M.; Kerekes, I.; Olah,
J. A. J. Org. Chem. 1979, 44, 3872. Olah, G. A.; Li, X.-Y. In Synthetic
Fluorine Chemistry; Olah, G. A., Chambers, R. D., Prakash, G. K. S., Eds.;
Wiley: New York, 1992; Chapter 8, p 163 and references therein.
5) Olah, G. A.; Li, X.-Y. Synlett. 1990, 267.
(8) Meerwein, H. In Houben-Weyl, Methoden der Organischen Chemie, 4th
ed.; Muller, E., Ed.; Thieme: Stuttgart, 1965; Vol. VI/3, p 329. Perst, H.
Oxonium Ion in Organic Chemistry; Verlag: Weinhein, 1971.
(9) Olah, G. A.; White, A. M.; O′Brien, D. H. Chem. ReV. 1970, 70, 561.
Olah, G. A.; Laali, K. K.; Wang, Q.; Prakash, G. K. S. Onium Ions;
Wiley: 1998; p 101.
(
(
(
6) Olah, G. A.; Li, X.-Y.; Wang, Q.; Prakash, G. K. S. Synthesis 1993, 693.
7) Yoneda, N.; Abe, T.; Fukuhara, T.; Suzuki, A. Chem. Lett. 1983, 1135.
Yoneda, N.; Nagata, S.; Fukuhara, T.; Suzuki, A. Chem. Lett. 1984, 1241.
Wiechert, D.; Mootz, D.; Dahlems, T. J. Am. Chem. Soc. 1997, 119, 12665.
(10) Saito, A. Japanese Patent, 1975, 50-126796. Saito, A. Japanese Patent, 1975,
50-126799.
7728
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J. AM. CHEM. SOC. 2002, 124, 7728-7736
10.1021/ja0124109 CCC: $22.00 © 2002 American Chemical Society