2,3,5,6-Tetrafluorophenylnitren-4-yl: A quartet-ground-state nitrene radical

Article abstract of DOI:10.1002/1521-3773(20020802)41:15<2742::AID-ANIE2742>3.0.CO;2-U

Elements of a carbene and a nitrene are linked by a common delocalized π electron in the molecule described here (see picture). The organic high-spin molecule with a quartet ground state could be photochemically generated and spectroscopically characteriz

Full text of DOI:10.1002/1521-3773(20020802)41:15<2742::AID-ANIE2742>3.0.CO;2-U

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‡
performed to detect heterodimer radical cation [1 ¥ 4 ¥ Sc2(OTf)5] at
m/z 1364 (Figure 1d). Control experiments of substrate 1 and product
3 in the presence of Sc(OTf)3 showed no signals that could be assigned
to the proposed radical intermediate in the case of the heterodimer
radical complex ion. In the case of the monomer radical complex ion,
the substrate 1 showed signals that can be assigned to this ion, possibly
tetrafluorophenylnitren-4-yl (1), which is formally generated
by substituting a nitrogen atom for an oxygen atom in
tetrafluorooxocyclohexadienylidene (2).
À
by homolytic cleavage of the C I bond in the heated capillary.
However, the intensity of these signals is only about one tenth of that
in the case of the reaction.
[27] The water and diethyl ether adduct complex ions ([M ¥ Sc(OTf)2 ¥
‡
‡
H2O] , [M ¥ Sc(OTf)2 ¥ Et2O] ) indicate two special features: a rising
front peak flank and a negative mass shift. Both phenomena are
observed only with quadrupole ion trap analyzers and with partic-
ularly unstable (easily fragmentable) ions.
[28] W. B. Motherwell, D. Crich, Free Radical Chain Reactions in Organic
Synthesis, Academic Press, London, 1992, pp. 179 212.
[29] C. Chatgilialoglu in Radicals in Organic Synthesis (Eds. P. Renaud,
M. P. Sibi), Wiley-VCH, Weinheim, 2001, pp. 28 49.
[30] Glutarate
6
(20 mmol, 1 ¥ 10À3 m), scandium triflate (24 mmol,
1.2 equiv), and tert-butyl iodide (80 mmol, 4 equiv) were dissolved in
diethyl ether (20 mL). The solution was cooled to 08C and saturated
with air by using a glass syringe. A solution of triethyl borane
(50 mmol, 2.5 equiv) and tris(trimethylsilyl)silane (80 mmol, 4 equiv)
was prepared in diethyl ether (20 mL) under argon. The reaction and
measurement were performed as described in refs. [23] and [26]. The
For compound 2, a triplet ground state has been determined
experimentally by using ESR[10] and IR spectroscopy[11], as
well as theoretically based on quantum-chemical calculations.
The electronic structure of 2 can be described by the
resonance structures 2A (carbene) and 2B (phenyl/phenoxyl
diradical). For the nitrene radical 1, which bears an additional
unpaired electron, DFT calculations predict a quartet ground
state 2.7kcalmol À1 below the lowest doublet state (UB3LYP/
6-311G(d,p) ‡ ZPE). The electronic structure of 1 is also
qualitatively represented by two resonance structures: struc-
ture 1A corresponds to a combination of a carbene with an
iminyl radical, structure 1B to that of a nitrene and a phenyl
radical. Two electrons are localized in the s plane, one at the
nitrogen atom (iminyl radical), the other at the C4 atom of the
phenyl ring (phenyl radical). The third unpaired electron is
delocalized over the p system and exhibits high spin densities
at the nitrogen atom as well as at the C4 atom. Thus, 1 can be
represented by the electronic structure of a delocalized
carbene (1A) and a delocalized nitrene (1B), which share a
common p electron. Both carbenes and nitrenes have similar
structures: open-shell systems with triplet ground states, and
thus the parallel alignment of the spins of all three electrons is
energetically most favorable; this leads to a quartet ground
state.
‡
MS/MS spectrum of m/z 654 ([8 ¥ Sc(OTf)2] , Figure 2b) and of m/z
‡
1400 ([6 ¥ 8 ¥ Sc2(OTf)5] , Figure 2c) were obtained. Control measure-
ments of substrate 6 and product 7 in the presence of Sc(OTf)3 showed
no signals that can be assigned to the monomeric and heterodimeric
radical complex ions.
[31] The shape of the peak at m/z 597provides unambiguous evidence for
the addition of diethyl ether to the complex ion with m/z 524; see also
ref. [27].
2,3,5,6-Tetrafluorophenylnitren-4-yl: A
Quartet-Ground-State Nitrene Radical**
Hans Henning Wenk and Wolfram Sander*
Dedicated to Professor Walter Siebert
on the occasion of his 65th birthday
The interaction of unpaired electrons coupled by conju-
Photolysis of aryl azides in cryogenic matrices is a well-
gated p-systems has been studied intensively during the last
3]
decade.[1 Also, a few heterospin systems combining differ-
established method for the generation of triplet aryl ni-
14]
trenes.[12
Short-wavelength irradiation of aryl iodides has
ent spin-carrying units within one molecule have been
described. As these studies were aimed at the development
of molecular magnets,[4] stable organic radicals were utilized,
which were coupled to photochemically generated nitrene[5, 6]
recently been applied to generate various fluorinated phenyl
radicals and didehydrobenzenes, which were studied by
matrix-isolation spectroscopy.[15, 16] Therefore, 4-iodo-2,3,5,6-
tetrafluoroazidobenzene (7; see Scheme 2) was used as a
precursor for 1. The perfluorinated system was chosen
because, in contrast to the unsubstituted phenylnitrene
(3),[12, 17] for 2,6-difluorinated phenylnitrene derivatives the
irreversible ring expansion to the corresponding didehydroa-
zepine (4; Scheme 1) was not observed under the conditions
of matrix isolation.[13, 14, 18] Instead, 2,6-difluorophenylnitrene
and pentafluorophenylnitrene (5) react reversibly to the
azirine derivatives (6) upon irradiation with light of wave-
length 444 nm.[14]
9]
or carbene[7 units through m- or p-phenylene linkers.
Systems containing highly reactive radicals (e.g. the phenyl
radical) in addition to a nitrene or carbene have not been
investigated so far. A molecule of this type is 2,3,5,6-
[*] Prof. Dr. W. Sander, Dipl.-Chem. H. H. Wenk
Lehrstuhl f¸r Organische Chemie II
Ruhr-Universit‰t Bochum
44780 Bochum (Germany)
Fax : (‡49)234-321-4353
E-mail: wolfram.sander@ruhr-uni-bochum.de
The IR spectrum of 7, matrix isolated in solid argon at 3 K,
exhibits the characteristic n(NN) vibration of the azido group
at 2131 cmÀ1 (Figure 1a). The absorptions of 7 disappear upon
[**] This work was financially supported by the Deutsche Forschungsge-
meinschaft and the Fonds der Chemischen Industrie. We thank
Professor W. T. Borden for the discussion of the high-spin system.
2742
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Angew. Chem. Int. Ed. 2002, 41, No. 15

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Scheme 1. Difference in reactivities between unfluorinated and fluorinat-
ed phenylnitrenes.
Scheme 2. Photoreaction of 7 and the subsequent chemistry.
Table 1. IR spectroscopic data of T-8.
[a]
[a,b]
[c]
[b,c]
Mode Symmetry nÄexp. [cmÀ1
]
Irel.,exp.
nÄcalcd [cmÀ1
]
Irel.,calcd
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
a1
b1
a2
b1
b2
a1
b2
a1
b2
b2
a1
a1
a1
b2
b2
a1
599.4
À
0.07599.1
0.01
À
610.4
644.3
669.3
738.1
811.8
0.00
0.00
0.00
0.00
0.23
0.54
0.00
0.00
0.00
0.06
0.18
0.13
À
À
À
À
À
À
817.3
958.0
À
0.37
1.00
969.8
À
1125.3
1146.8
1287.1
1294.1
1338.8
1404.1
À
À
À
À
Figure 1. Photochemistry of 7. a) IR spectrum of 7 (Ar, 3 K). b) Difference
spectrum. Bands pointing upwards appear, bands pointing downwards
disappear upon irradiation with light of wavelength 320 nm for 17h.
c) Calculated (UB3LYP/6 311G(d,p), unscaled) spectrum of 4-iodo-
2,3,5,6-tetrafluorophenylnitrene T-8.
1283.5
1332.2
1398.2
0.14
0.42
0.14
1458.2
0.85
0.18
1444.70.85
1521.6
1597.3
1.00
1545.9
1607.3
0.54
0.27
[a] Argon matrix, 3 K. [b] Relative intensity based on the most intense
absorption. [c] Calculated at the UB3LYP/6 311G(d,p) level of theory,
unscaled. The assignment is tentative and is based on band positions and
intensities.
photolysis with light of 320 nm wavelength, while a new
compound with intense IR bands at 958, 1445, and 1522 cmÀ1
is formed concurrently. In the UV/Vis spectrum the reaction is
accompanied by decrease of the absorption of 7 at 238 nm and
the formation of new bands at 257, 293, and 310 nm, as well as
two broad absorptions in the 320 360 nm and 390 460 nm
region. The new species does not exhibit the characteristic IR
absorptions of a didehydroazepine[12, 17] or an azirine[14] (which
are potential photoproducts of phenylnitrene derivatives),
however it does show the typical ESR signals of a triplet
nitrene[19] with the zero-field parameters jD/hc jˆ 1.103 cmÀ1
and jE/hc jˆ 0.012 cmÀ1. Therefore, the spectrum of the newly
formed compound is assigned to the triplet 4-iodo-2,3,5,6-
tetrafluorophenylnitrene T-8 (Scheme 2). This interpretation
is supported by the calculated IR spectrum, which nicely
reproduces the experimental data (Figure 1b,c, Table 1).
Subsequent monochromatic short-wavelength irradiation
with light of wavelength 254 nm results in a decrease of the
bands of T-8 and formation of new absorptions, which are
assigned to two sets of bands A and B by comparison of the
relative intensities in several experiments (Figure 2a). Data
set A exhibits IR absorptions in the region from 948 to
1546 cmÀ1 which decrease again upon annealing of the matrix
at 32 K, reforming T-8. The UV spectrum does not yield
additional information because of rapid deterioration of the
optical quality of the matrix upon short wavelength irradi-
ation. The reversibility of the reaction upon annealing of the
Figure 2. Photochemistry of T-8. a) Difference spectrum. Bands pointing
upwards appear, bands pointing downwards disappear upon irradiation of
T-2 in an argon matrix at 3 K with light of wavelength 254 nm. Band set A is
marked with circles, set B with triangles. b) Calculated (UB3LYP/6
311G(d,p), unscaled) spectrum of quartet nitrene radical Q-1. c) Calculated
(UB3LYP/6 311G(d,p), unscaled) spectrum of doublet nitrene radical
D-1.
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matrix indicates cleavage of the C-I bond, and the observed
IR spectrum is in excellent agreement with the calculated
spectrum of quartet nitrene radical Q-1 (Figure 2b, Table 2).
In contrast, there is less agreement with the calculated data
for the doublet state D-1 (Figure 2c), especially in the region
between 900 and 1100 cmÀ1.
length 254 nm, although it was established by theoretical[18] as
well as experimental[13, 14] studies that this reaction should not
occur for 2,6-difluorinated phenylnitrenes in cryogenic ma-
trices. In solution a significantly increased barrier for this
reaction was observed with less fluorinated starting materi-
als.[21] Nevertheless, comparison with the calculated spectrum
of 9 confirms that the formation of the seven-membered ring
is apparently possible in this case (Figure 3, Table 3). Accord-
ing to calculations (B3LYP/6-311G(d,p) ‡ ZPE), the reaction
T-8 !9 is endothermic by 7.5 kcalmolÀ1.
Table 2. IR spectroscopic data of the quartet nitrene radical Q-1.
[a]
[a,b]
[c]
[b,c]
Mode Symmetry nÄexp. [cmÀ1
]
Irel.,exp.
nÄcalcd [cmÀ1
]
Irel.,calcd
18
19
20
21
22
23
24
25
26
b2
a1
b2
a1
b2
a1
a1
b2
b2
948.0
1080.4
À
0.52
0.15
À
956.4
1089.6
1143.5
1280.6
1296.9
1324.5
1398.8
1.00
0.45
0.20
0.03
0.01
0.00
0.13
0.23
Table 3. IR spectroscopic data of 9.
[a]
[a,b]
[c]
[b,c]
Mode
nÄexp. [cmÀ1
]
Irel.,exp.
nÄcalcd [cmÀ1
]
Irel.,calcd
À
À
À
À
18
19
20
21
22
23
24
669.1
706.1
795.9
883.70.50
1083.70.09
1125.5
0.05
0.13
0.31
691.1
724.2
786.3
0.19
0.02
0.05
0.18
1315.2
1389.0
0.19
0.15
1434.71.00
1545.5
1443.5
0.15
894.5
1088.2
0.19
0.16
1266.1
1575.4
0.34
0.11
1141.0
1278.7
0.21
0.12
0.08
[a] [c] See footnotes for Table 1
1259.9
The second photoproduct B, which does not decrease upon
annealing of the matrix, has a prominent absorption at
25
26
271361.2
1310.1
1318.5
0.43
0.24
1326.5
1332.0
1.00
1.00
1535.70.14
0.23
0.15
À1
0.64 .0
1365.4
0.06
1367
ˆ
1854 cm . The n(C N) vibration of didehydroazepine 4,
which arises upon photolysis of azidobenzene in cryogenic
matrices in addition to phenylnitrene 3, is observed at a
similar frequency.[12, 17] When the experiment is carried out in
a neon matrix, B is the exclusive product of the short-
wavelength irradiation of T-8, while nitrene radical Q-1 is not
observed (Figure 3).[20] This allows us to unambiguously
28
29
30
1528.0
1565.70.48
1854.1
15830.734
0.16
1930.3
0.33
[a] Neon matrix, 3 K. [b, c] See footnotes for Table 1.
Comparison of the calculated geometries of tetrafluorooxo-
cyclohexadienylidene (2) and the nitrene radical 1 shows that
there is not only a formal resemblance of both compounds
ˆ
ˆ
(Figure 4). With the exception of the C O and C N bonds,
Figure 3. Photochemistry of T-2. a) Difference spectrum. Bands pointing
upwards appear, bands pointing downwards disappear upon irradiation of
T-2 in a neon matrix at 3 K with light of wavelength 254 nm. b) Calculated
(B3LYP/6 311G(d,p), unscaled) spectrum of didehydroazepine (3).
Figure 4. Comparison of the calculated geometries (a) and spin density
distributions (b) in nitrene radical Q-1 and carbene T-2 (UB3LYP/6
311G(d,p)). Bond lengths [ä], bond angles [8].
distinguish the absorption spectra of A and B. In particular, it
can be discounted that the IR band at 884 cmÀ1, the assign-
ment of which to 1 would complicate the discrimination
between doublet-1 and quartet-1 based on IR spectra, is
caused by the nitrene radical.
The absorption at 1854 cmÀ1 indicates rearrangement of T-8
to the ring-expanded 5-iodo-3,4,6,7-tetrafluorodidehydroaze-
pine (9; see Scheme 2) upon photolysis with light of wave-
the structures of 1 and 2 are almost identical, the differences
À
in C C bond lengths and bond angles being well below 0.1 ä
and 28, respectively. The spin-density distribution also reflects
the similarity of both molecules, with differences appearing
only at the nitrogen and oxygen atoms (Figure 4). In the
carbene 2 the spin density at the oxygen atom is predominantly
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[10] H. H. Wenk, R. H¸bert, W. Sander, J. Org. Chem. 2001, 66, 7994
7999.
[11] W. Sander, R. H¸bert, E. Kraka, J. Grafenstein, D. Cremer, Chem.
Eur. J. 2000, 6, 4567 4579.
[12] J. C. Hayes, R. S. Sheridan, J. Am. Chem. Soc. 1990, 112, 5879 5881.
[13] I. R. Dunkin, P. C. P. Thomson, J. Chem. Soc. Chem. Commun. 1982,
1192 1193.
[14] J. Morawietz, W. Sander, J. Org. Chem. 1996, 61, 4351 4354.
[15] H. H. Wenk, A. Balster, W. Sander, D. A. Hrovat, W. T. Borden,
Angew. Chem. 2001, 113, 2356 2359; Angew. Chem. Int. Ed. 2001, 40,
2295 2298.
[16] H. H. Wenk, W. Sander, Chem. Eur. J. 2001, 7, 1837 1844.
[17] O. L. Chapman, J. P. Le Roux, J. Am. Chem. Soc. 1978, 100, 282 285.
[18] W. T. Borden, W. L. Karney, J. Am. Chem. Soc. 1997, 119, 3347 3350.
[19] M. S. Platz in CRC Handbook of Organic Photochemistry, Vol. II (Ed.:
J. C. Scaiano), CRC Press, Boca Raton, FL, USA, 1989, S. 373 393.
[20] In contrast, photolysis of fluorinated diiodobenzene derivatives leads
to the corresponding radicals and diradicals in solid neon but not in
argon, see references [15,16].
[21] N. P. Gritsan, A. D. Gudmundsdottir, D. Tigelaar, Z. D. Zhu, W. L.
Karney, C. M. Hadad, M. S. Platz, J. Am. Chem. Soc. 2001, 123, 1951
1962.
[22] I. R. Dunkin, Matrix Isolation Techniques: A Practical Approach,
Oxford University Press, Oxford, 1998.
[23] Gaussian98 (RevisionA.7), M. J. Frisch, G. W. Trucks, H. B. Schlegel,
G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A.
Montgomery, R. E. Stratmann, J. C. Burant, S. Dapprich, J. M.
Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi,
V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo,
S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K.
Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. Cioslowski, J. V. Ortiz, A. G. Baboul, B. B. Stefanov, G.
Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill, B. G.
Johnson, W. Chen, M. W. Wong, J. L. Andres, M. Head-Gordon, E. S.
Replogle, J. A. Pople, Gaussian, Inc., Pittsburgh, PA, 1998..
localized in the p orbital perpendicular to the ring plane, while
in 1 the highest spin density is in the ring plane.
Photolysis of 4-iodo-2,3,5,6-tetrafluoroazidobenzene (7) of-
fers an access to the until now unknown C6F4N potential energy
surface and to the unusual high-spin nitrene radical 1. The
influence of different topologies and substituents on the spin
state of nitrene radicals will be investigated in future studies.
Experimental Section
Matrix experiments were carried out according to standard techniques[22]
using a Sumitomo Heavy Industries RDK-408D closed-cycle cryostat. The
lowest temperature available with this system is 2.7K. Matrices were
produced by codeposition of a large excess of neon or argon (Messer-
Griesheim, 99.9999%) and the substance to be isolated on top of a cold CsI
window. During deposition of argon matrices the temperature of the
window was maintained at 30 K. Argon matrices for ESR spectroscopy
were deposited at 13 K on a 2 mm OFHC-copper rod, cooled by an APD-
HC2 closed-cycle cryostat. IR spectra were recorded with a Bruker
Equinox 55 FTIR spectrometer with a resolution of 0.5 cmÀ1 in the range of
400 4000 cmÀ1. ESR spectra were recorded with a Bruker Elexsys E500
spectrometer. Irradiations were carried out with a Gr‰ntzel low-pressure
mercury lamp (254 nm) and an Osram HBO-500-W/2 high-pressure
mercury arc lamp in an Oriel housing with quartz optics, a dichroic mirror,
and a Schott cutoff filter (320 nm). DFT calculations were performed with
the Gaussian 98 suite of programs.[23]
4-Iodo-2,3,5,6-tetrafluoroaniline: Yellow HgO (12.8 g, 59.1 mmol) was
added to a solution of 2,3,5,6-tetrafluoroaniline (12.8 g, 77.6 mmol) in
ethanol (200 mL). The solution was vigorously stirred and iodine (19.8 g,
78.0 mmol) added. The mixture was stirred overnight and filtered over
celite. After addition of Na2SO3 (1 g) the solution was concentrated to a
residual volume of 50 mL using a rotary evaporator. Water (200 mL) was
added and the precipitate was filtered off. Recrystallization from 25%
ethanol in water and subsequent drying in vacuo yielded 4-iodo-2,3,5,6-
tetrafluoroaniline (16.2 g, 55.7mmol, 72%) as dark crystals. MS: m/z(%):
‡
291 (M , 100), 164 (50), 144 (25), 137(60), 127(30), 117(25), 69 (20).
4-Iodo-2,3,5,6-tetrafluoroazidobenzene (7): 4-Iodo-2,3,5,6-tetrafluoroani-
line (3.0 g, 10.3 mmol) was dissolved in trifluoroacetic acid (30 mL) and
cooled to 08C. A solution of sodium nitrite (0.81 g, 11.7mmol) in water
(15 mL) was slowly added while stirring and cooling with an ice bath. The
solution was stirred for further 15 min at 08C. A solution of sodium azide
(0.75 g, 11.5 mmol) in water (15 mL) was added to the stirred solution,
which was subsequently stirred for 1 h at room temperature. After addition
of ether (100 mL) the organic phase was washed with water and dilute
aqueous NaOH, dried (Na2SO4), and evaporated. Chromatography (silica/
Conversion of Hexafluoropropene into
1,1,1-Trifluoropropane by Rhodium-Mediated
À
C F Activation**
‡
Thomas Braun,* Daniel Noveski, Beate Neumann,
and Hans-Georg Stammler
pentane) yielded 7 (2.18 g, 67%) as a colorless oil. MS: m/z (%): 317( M ,
10), 289 (30), 162 (100), 127(30), 117(20), 112 (10), 98 (25), 69 (25).
13C NMR (CDCl3, 50 MHz): d ˆ 66.3 (t, J ˆ 28.0 Hz), 120.5 (tt, J ˆ 2.9 Hz,
12.3 Hz), 140.0 (dm, 256.4 Hz), 147.2 ppm (dm, 248.1 Hz). IR (Ar, 3 K): nÄ
(%): 2229.9 (5), 2196.8 (5), 2130.9 (100), 2112.4 (18), 1634.5 (10), 1492.2
(95), 1478.4 (49), 1307.6 (15), 1223.2 (31), 1012.1 (31), 1001.9 (13), 974.3
Interest in the activation of carbon fluorine bonds by
transition metal centers has been increasing dramatically over
the last decade.[1] Recent discoveries include the stochiomet-
ric[2] and catalytic[3, 4] derivatization of aromatic compounds
À1
(39), 955.3 (6), 807.8 (11), 768.3 (22), 664.5 cm (5).
Received: February 1, 2002 [Z18625]
[*] Dr. T. Braun, Dipl.-Chem. D. Noveski, B. Neumann,
Dr. H.-G. Stammler
[1] a) H. Iwamura, Adv. Phys. Org. Chem. 1990, 179 253; b) H. Iwamura,
J. Phys. Org. Chem. 1998, 11, 299 304.
[2] D. A. Dougherty, Acc. Chem. Res. 1991, 24, 88 94.
[3] A. Rajca, Chem. Rev. 1994, 94, 871 893.
[4] Magnetism: Molecules to Materials (Eds.: J. S. Miller, M. Drillon),
Wiley-VCH, Weinheim, 2001.
[5] P. M. Lahti, B. Esat, R. Walton, J. Am. Chem. Soc. 1998, 120, 5122
5123.
[6] P. M. Lahti, B. Esat, Y. Liao, P. Serwinski, J. Lan, R. Walton,
Polyhedron 2001, 20, 1647 1652.
[7] K. Matsuda, H. Iwamura, Chem. Commun. 1996, 1131 1132.
[8] K. Matsuda, H. Iwamura, Mol. Cryst. Liq. Cryst. 1997, 306, 89 94.
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1998, 1581 1588.
Fakult‰t f¸r Chemie
Universit‰t Bielefeld
Postfach 100131, 33501 Bielefeld (Germany)
Fax : (‡49)521-106-6026
E-mail: thomas.braun@uni-bielefeld.de
[**] This work was supported by the Deutsche Forschungsgemeinschaft
(grant BR-2065/1-2) and the Fonds der Chemischen Industrie. We
thank Professor G.-V. Rˆschenthaler for a gift of hexafluoropropene
and DMC2 for a loan of RhCl3. T.B. also thanks Professor P. Jutzi for
his generous support.
Supporting information for this article is available on the WWW under
http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2002, 41, No. 15
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2745